Move routines to manipulate WAL into PostgreSQL::Test::Cluster

[pgsql.git] / src / interfaces / libpq / fe-secure-openssl.c

/*-------------------------------------------------------------------------
 *
 * fe-secure-openssl.c
 *        OpenSSL support
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        src/interfaces/libpq/fe-secure-openssl.c
 *
 * NOTES
 *
 *        We don't provide informational callbacks here (like
 *        info_cb() in be-secure-openssl.c), since there's no good mechanism to
 *        display such information to the user.
 *
 *-------------------------------------------------------------------------
 */

#include "postgres_fe.h"

#include <signal.h>
#include <fcntl.h>
#include <ctype.h>

#include "libpq-fe.h"
#include "fe-auth.h"
#include "fe-secure-common.h"
#include "libpq-int.h"

#ifdef WIN32
#include "win32.h"
#else
#include <sys/socket.h>
#include <unistd.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#endif

#include <sys/stat.h>

#ifdef WIN32
#include "pthread-win32.h"
#else
#include <pthread.h>
#endif

/*
 * These SSL-related #includes must come after all system-provided headers.
 * This ensures that OpenSSL can take care of conflicts with Windows'
 * <wincrypt.h> by #undef'ing the conflicting macros.  (We don't directly
 * include <wincrypt.h>, but some other Windows headers do.)
 */
#include "common/openssl.h"
#include <openssl/conf.h>
#ifdef USE_SSL_ENGINE
#include <openssl/engine.h>
#endif
#include <openssl/x509v3.h>


static int      verify_cb(int ok, X509_STORE_CTX *ctx);
static int      openssl_verify_peer_name_matches_certificate_name(PGconn *conn,
                                                                                                                          ASN1_STRING *name_entry,
                                                                                                                          char **store_name);
static int      openssl_verify_peer_name_matches_certificate_ip(PGconn *conn,
                                                                                                                        ASN1_OCTET_STRING *addr_entry,
                                                                                                                        char **store_name);
static int      initialize_SSL(PGconn *conn);
static PostgresPollingStatusType open_client_SSL(PGconn *conn);
static char *SSLerrmessage(unsigned long ecode);
static void SSLerrfree(char *buf);
static int      PQssl_passwd_cb(char *buf, int size, int rwflag, void *userdata);

static int      pgconn_bio_read(BIO *h, char *buf, int size);
static int      pgconn_bio_write(BIO *h, const char *buf, int size);
static BIO_METHOD *pgconn_bio_method(void);
static int      ssl_set_pgconn_bio(PGconn *conn);

static pthread_mutex_t ssl_config_mutex = PTHREAD_MUTEX_INITIALIZER;

static PQsslKeyPassHook_OpenSSL_type PQsslKeyPassHook = NULL;
static int      ssl_protocol_version_to_openssl(const char *protocol);

/* ------------------------------------------------------------ */
/*                       Procedures common to all secure sessions                       */
/* ------------------------------------------------------------ */

PostgresPollingStatusType
pgtls_open_client(PGconn *conn)
{
        /* First time through? */
        if (conn->ssl == NULL)
        {
                /*
                 * Create a connection-specific SSL object, and load client
                 * certificate, private key, and trusted CA certs.
                 */
                if (initialize_SSL(conn) != 0)
                {
                        /* initialize_SSL already put a message in conn->errorMessage */
                        pgtls_close(conn);
                        return PGRES_POLLING_FAILED;
                }
        }

        /* Begin or continue the actual handshake */
        return open_client_SSL(conn);
}

ssize_t
pgtls_read(PGconn *conn, void *ptr, size_t len)
{
        ssize_t         n;
        int                     result_errno = 0;
        char            sebuf[PG_STRERROR_R_BUFLEN];
        int                     err;
        unsigned long ecode;

rloop:

        /*
         * Prepare to call SSL_get_error() by clearing thread's OpenSSL error
         * queue.  In general, the current thread's error queue must be empty
         * before the TLS/SSL I/O operation is attempted, or SSL_get_error() will
         * not work reliably.  Since the possibility exists that other OpenSSL
         * clients running in the same thread but not under our control will fail
         * to call ERR_get_error() themselves (after their own I/O operations),
         * pro-actively clear the per-thread error queue now.
         */
        SOCK_ERRNO_SET(0);
        ERR_clear_error();
        n = SSL_read(conn->ssl, ptr, len);
        err = SSL_get_error(conn->ssl, n);

        /*
         * Other clients of OpenSSL may fail to call ERR_get_error(), but we
         * always do, so as to not cause problems for OpenSSL clients that don't
         * call ERR_clear_error() defensively.  Be sure that this happens by
         * calling now.  SSL_get_error() relies on the OpenSSL per-thread error
         * queue being intact, so this is the earliest possible point
         * ERR_get_error() may be called.
         */
        ecode = (err != SSL_ERROR_NONE || n < 0) ? ERR_get_error() : 0;
        switch (err)
        {
                case SSL_ERROR_NONE:
                        if (n < 0)
                        {
                                /* Not supposed to happen, so we don't translate the msg */
                                appendPQExpBufferStr(&conn->errorMessage,
                                                                         "SSL_read failed but did not provide error information\n");
                                /* assume the connection is broken */
                                result_errno = ECONNRESET;
                        }
                        break;
                case SSL_ERROR_WANT_READ:
                        n = 0;
                        break;
                case SSL_ERROR_WANT_WRITE:

                        /*
                         * Returning 0 here would cause caller to wait for read-ready,
                         * which is not correct since what SSL wants is wait for
                         * write-ready.  The former could get us stuck in an infinite
                         * wait, so don't risk it; busy-loop instead.
                         */
                        goto rloop;
                case SSL_ERROR_SYSCALL:
                        if (n < 0 && SOCK_ERRNO != 0)
                        {
                                result_errno = SOCK_ERRNO;
                                if (result_errno == EPIPE ||
                                        result_errno == ECONNRESET)
                                        libpq_append_conn_error(conn, "server closed the connection unexpectedly\n"
                                                                                        "\tThis probably means the server terminated abnormally\n"
                                                                                        "\tbefore or while processing the request.");
                                else
                                        libpq_append_conn_error(conn, "SSL SYSCALL error: %s",
                                                                                        SOCK_STRERROR(result_errno,
                                                                                                                  sebuf, sizeof(sebuf)));
                        }
                        else
                        {
                                libpq_append_conn_error(conn, "SSL SYSCALL error: EOF detected");
                                /* assume the connection is broken */
                                result_errno = ECONNRESET;
                                n = -1;
                        }
                        break;
                case SSL_ERROR_SSL:
                        {
                                char       *errm = SSLerrmessage(ecode);

                                libpq_append_conn_error(conn, "SSL error: %s", errm);
                                SSLerrfree(errm);
                                /* assume the connection is broken */
                                result_errno = ECONNRESET;
                                n = -1;
                                break;
                        }
                case SSL_ERROR_ZERO_RETURN:

                        /*
                         * Per OpenSSL documentation, this error code is only returned for
                         * a clean connection closure, so we should not report it as a
                         * server crash.
                         */
                        libpq_append_conn_error(conn, "SSL connection has been closed unexpectedly");
                        result_errno = ECONNRESET;
                        n = -1;
                        break;
                default:
                        libpq_append_conn_error(conn, "unrecognized SSL error code: %d", err);
                        /* assume the connection is broken */
                        result_errno = ECONNRESET;
                        n = -1;
                        break;
        }

        /* ensure we return the intended errno to caller */
        SOCK_ERRNO_SET(result_errno);

        return n;
}

bool
pgtls_read_pending(PGconn *conn)
{
        return SSL_pending(conn->ssl) > 0;
}

ssize_t
pgtls_write(PGconn *conn, const void *ptr, size_t len)
{
        ssize_t         n;
        int                     result_errno = 0;
        char            sebuf[PG_STRERROR_R_BUFLEN];
        int                     err;
        unsigned long ecode;

        SOCK_ERRNO_SET(0);
        ERR_clear_error();
        n = SSL_write(conn->ssl, ptr, len);
        err = SSL_get_error(conn->ssl, n);
        ecode = (err != SSL_ERROR_NONE || n < 0) ? ERR_get_error() : 0;
        switch (err)
        {
                case SSL_ERROR_NONE:
                        if (n < 0)
                        {
                                /* Not supposed to happen, so we don't translate the msg */
                                appendPQExpBufferStr(&conn->errorMessage,
                                                                         "SSL_write failed but did not provide error information\n");
                                /* assume the connection is broken */
                                result_errno = ECONNRESET;
                        }
                        break;
                case SSL_ERROR_WANT_READ:

                        /*
                         * Returning 0 here causes caller to wait for write-ready, which
                         * is not really the right thing, but it's the best we can do.
                         */
                        n = 0;
                        break;
                case SSL_ERROR_WANT_WRITE:
                        n = 0;
                        break;
                case SSL_ERROR_SYSCALL:

                        /*
                         * If errno is still zero then assume it's a read EOF situation,
                         * and report EOF.  (This seems possible because SSL_write can
                         * also do reads.)
                         */
                        if (n < 0 && SOCK_ERRNO != 0)
                        {
                                result_errno = SOCK_ERRNO;
                                if (result_errno == EPIPE || result_errno == ECONNRESET)
                                        libpq_append_conn_error(conn, "server closed the connection unexpectedly\n"
                                                                                        "\tThis probably means the server terminated abnormally\n"
                                                                                        "\tbefore or while processing the request.");
                                else
                                        libpq_append_conn_error(conn, "SSL SYSCALL error: %s",
                                                                                        SOCK_STRERROR(result_errno,
                                                                                                                  sebuf, sizeof(sebuf)));
                        }
                        else
                        {
                                libpq_append_conn_error(conn, "SSL SYSCALL error: EOF detected");
                                /* assume the connection is broken */
                                result_errno = ECONNRESET;
                                n = -1;
                        }
                        break;
                case SSL_ERROR_SSL:
                        {
                                char       *errm = SSLerrmessage(ecode);

                                libpq_append_conn_error(conn, "SSL error: %s", errm);
                                SSLerrfree(errm);
                                /* assume the connection is broken */
                                result_errno = ECONNRESET;
                                n = -1;
                                break;
                        }
                case SSL_ERROR_ZERO_RETURN:

                        /*
                         * Per OpenSSL documentation, this error code is only returned for
                         * a clean connection closure, so we should not report it as a
                         * server crash.
                         */
                        libpq_append_conn_error(conn, "SSL connection has been closed unexpectedly");
                        result_errno = ECONNRESET;
                        n = -1;
                        break;
                default:
                        libpq_append_conn_error(conn, "unrecognized SSL error code: %d", err);
                        /* assume the connection is broken */
                        result_errno = ECONNRESET;
                        n = -1;
                        break;
        }

        /* ensure we return the intended errno to caller */
        SOCK_ERRNO_SET(result_errno);

        return n;
}

char *
pgtls_get_peer_certificate_hash(PGconn *conn, size_t *len)
{
        X509       *peer_cert;
        const EVP_MD *algo_type;
        unsigned char hash[EVP_MAX_MD_SIZE];    /* size for SHA-512 */
        unsigned int hash_size;
        int                     algo_nid;
        char       *cert_hash;

        *len = 0;

        if (!conn->peer)
                return NULL;

        peer_cert = conn->peer;

        /*
         * Get the signature algorithm of the certificate to determine the hash
         * algorithm to use for the result.  Prefer X509_get_signature_info(),
         * introduced in OpenSSL 1.1.1, which can handle RSA-PSS signatures.
         */
#if HAVE_X509_GET_SIGNATURE_INFO
        if (!X509_get_signature_info(peer_cert, &algo_nid, NULL, NULL, NULL))
#else
        if (!OBJ_find_sigid_algs(X509_get_signature_nid(peer_cert),
                                                         &algo_nid, NULL))
#endif
        {
                libpq_append_conn_error(conn, "could not determine server certificate signature algorithm");
                return NULL;
        }

        /*
         * The TLS server's certificate bytes need to be hashed with SHA-256 if
         * its signature algorithm is MD5 or SHA-1 as per RFC 5929
         * (https://tools.ietf.org/html/rfc5929#section-4.1).  If something else
         * is used, the same hash as the signature algorithm is used.
         */
        switch (algo_nid)
        {
                case NID_md5:
                case NID_sha1:
                        algo_type = EVP_sha256();
                        break;
                default:
                        algo_type = EVP_get_digestbynid(algo_nid);
                        if (algo_type == NULL)
                        {
                                libpq_append_conn_error(conn, "could not find digest for NID %s",
                                                                                OBJ_nid2sn(algo_nid));
                                return NULL;
                        }
                        break;
        }

        if (!X509_digest(peer_cert, algo_type, hash, &hash_size))
        {
                libpq_append_conn_error(conn, "could not generate peer certificate hash");
                return NULL;
        }

        /* save result */
        cert_hash = malloc(hash_size);
        if (cert_hash == NULL)
        {
                libpq_append_conn_error(conn, "out of memory");
                return NULL;
        }
        memcpy(cert_hash, hash, hash_size);
        *len = hash_size;

        return cert_hash;
}

/* ------------------------------------------------------------ */
/*                                              OpenSSL specific code                                   */
/* ------------------------------------------------------------ */

/*
 *      Certificate verification callback
 *
 *      This callback allows us to log intermediate problems during
 *      verification, but there doesn't seem to be a clean way to get
 *      our PGconn * structure.  So we can't log anything!
 *
 *      This callback also allows us to override the default acceptance
 *      criteria (e.g., accepting self-signed or expired certs), but
 *      for now we accept the default checks.
 */
static int
verify_cb(int ok, X509_STORE_CTX *ctx)
{
        return ok;
}

#ifdef HAVE_SSL_CTX_SET_CERT_CB
/*
 * Certificate selection callback
 *
 * This callback lets us choose the client certificate we send to the server
 * after seeing its CertificateRequest.  We only support sending a single
 * hard-coded certificate via sslcert, so we don't actually set any certificates
 * here; we just use it to record whether or not the server has actually asked
 * for one and whether we have one to send.
 */
static int
cert_cb(SSL *ssl, void *arg)
{
        PGconn     *conn = arg;

        conn->ssl_cert_requested = true;

        /* Do we have a certificate loaded to send back? */
        if (SSL_get_certificate(ssl))
                conn->ssl_cert_sent = true;

        /*
         * Tell OpenSSL that the callback succeeded; we're not required to
         * actually make any changes to the SSL handle.
         */
        return 1;
}
#endif

/*
 * OpenSSL-specific wrapper around
 * pq_verify_peer_name_matches_certificate_name(), converting the ASN1_STRING
 * into a plain C string.
 */
static int
openssl_verify_peer_name_matches_certificate_name(PGconn *conn, ASN1_STRING *name_entry,
                                                                                                  char **store_name)
{
        int                     len;
        const unsigned char *namedata;

        /* Should not happen... */
        if (name_entry == NULL)
        {
                libpq_append_conn_error(conn, "SSL certificate's name entry is missing");
                return -1;
        }

        /*
         * GEN_DNS can be only IA5String, equivalent to US ASCII.
         */
        namedata = ASN1_STRING_get0_data(name_entry);
        len = ASN1_STRING_length(name_entry);

        /* OK to cast from unsigned to plain char, since it's all ASCII. */
        return pq_verify_peer_name_matches_certificate_name(conn, (const char *) namedata, len, store_name);
}

/*
 * OpenSSL-specific wrapper around
 * pq_verify_peer_name_matches_certificate_ip(), converting the
 * ASN1_OCTET_STRING into a plain C string.
 */
static int
openssl_verify_peer_name_matches_certificate_ip(PGconn *conn,
                                                                                                ASN1_OCTET_STRING *addr_entry,
                                                                                                char **store_name)
{
        int                     len;
        const unsigned char *addrdata;

        /* Should not happen... */
        if (addr_entry == NULL)
        {
                libpq_append_conn_error(conn, "SSL certificate's address entry is missing");
                return -1;
        }

        /*
         * GEN_IPADD is an OCTET STRING containing an IP address in network byte
         * order.
         */
        addrdata = ASN1_STRING_get0_data(addr_entry);
        len = ASN1_STRING_length(addr_entry);

        return pq_verify_peer_name_matches_certificate_ip(conn, addrdata, len, store_name);
}

static bool
is_ip_address(const char *host)
{
        struct in_addr dummy4;
#ifdef HAVE_INET_PTON
        struct in6_addr dummy6;
#endif

        return inet_aton(host, &dummy4)
#ifdef HAVE_INET_PTON
                || (inet_pton(AF_INET6, host, &dummy6) == 1)
#endif
                ;
}

/*
 *      Verify that the server certificate matches the hostname we connected to.
 *
 * The certificate's Common Name and Subject Alternative Names are considered.
 */
int
pgtls_verify_peer_name_matches_certificate_guts(PGconn *conn,
                                                                                                int *names_examined,
                                                                                                char **first_name)
{
        STACK_OF(GENERAL_NAME) * peer_san;
        int                     i;
        int                     rc = 0;
        char       *host = conn->connhost[conn->whichhost].host;
        int                     host_type;
        bool            check_cn = true;

        Assert(host && host[0]);        /* should be guaranteed by caller */

        /*
         * We try to match the NSS behavior here, which is a slight departure from
         * the spec but seems to make more intuitive sense:
         *
         * If connhost contains a DNS name, and the certificate's SANs contain any
         * dNSName entries, then we'll ignore the Subject Common Name entirely;
         * otherwise, we fall back to checking the CN. (This behavior matches the
         * RFC.)
         *
         * If connhost contains an IP address, and the SANs contain iPAddress
         * entries, we again ignore the CN. Otherwise, we allow the CN to match,
         * EVEN IF there is a dNSName in the SANs. (RFC 6125 prohibits this: "A
         * client MUST NOT seek a match for a reference identifier of CN-ID if the
         * presented identifiers include a DNS-ID, SRV-ID, URI-ID, or any
         * application-specific identifier types supported by the client.")
         *
         * NOTE: Prior versions of libpq did not consider iPAddress entries at
         * all, so this new behavior might break a certificate that has different
         * IP addresses in the Subject CN and the SANs.
         */
        if (is_ip_address(host))
                host_type = GEN_IPADD;
        else
                host_type = GEN_DNS;

        /*
         * First, get the Subject Alternative Names (SANs) from the certificate,
         * and compare them against the originally given hostname.
         */
        peer_san = (STACK_OF(GENERAL_NAME) *)
                X509_get_ext_d2i(conn->peer, NID_subject_alt_name, NULL, NULL);

        if (peer_san)
        {
                int                     san_len = sk_GENERAL_NAME_num(peer_san);

                for (i = 0; i < san_len; i++)
                {
                        const GENERAL_NAME *name = sk_GENERAL_NAME_value(peer_san, i);
                        char       *alt_name = NULL;

                        if (name->type == host_type)
                        {
                                /*
                                 * This SAN is of the same type (IP or DNS) as our host name,
                                 * so don't allow a fallback check of the CN.
                                 */
                                check_cn = false;
                        }

                        if (name->type == GEN_DNS)
                        {
                                (*names_examined)++;
                                rc = openssl_verify_peer_name_matches_certificate_name(conn,
                                                                                                                                           name->d.dNSName,
                                                                                                                                           &alt_name);
                        }
                        else if (name->type == GEN_IPADD)
                        {
                                (*names_examined)++;
                                rc = openssl_verify_peer_name_matches_certificate_ip(conn,
                                                                                                                                         name->d.iPAddress,
                                                                                                                                         &alt_name);
                        }

                        if (alt_name)
                        {
                                if (!*first_name)
                                        *first_name = alt_name;
                                else
                                        free(alt_name);
                        }

                        if (rc != 0)
                        {
                                /*
                                 * Either we hit an error or a match, and either way we should
                                 * not fall back to the CN.
                                 */
                                check_cn = false;
                                break;
                        }
                }
                sk_GENERAL_NAME_pop_free(peer_san, GENERAL_NAME_free);
        }

        /*
         * If there is no subjectAltName extension of the matching type, check the
         * Common Name.
         *
         * (Per RFC 2818 and RFC 6125, if the subjectAltName extension of type
         * dNSName is present, the CN must be ignored. We break this rule if host
         * is an IP address; see the comment above.)
         */
        if (check_cn)
        {
                X509_NAME  *subject_name;

                subject_name = X509_get_subject_name(conn->peer);
                if (subject_name != NULL)
                {
                        int                     cn_index;

                        cn_index = X509_NAME_get_index_by_NID(subject_name,
                                                                                                  NID_commonName, -1);
                        if (cn_index >= 0)
                        {
                                char       *common_name = NULL;

                                (*names_examined)++;
                                rc = openssl_verify_peer_name_matches_certificate_name(conn,
                                                                                                                                           X509_NAME_ENTRY_get_data(X509_NAME_get_entry(subject_name, cn_index)),
                                                                                                                                           &common_name);

                                if (common_name)
                                {
                                        if (!*first_name)
                                                *first_name = common_name;
                                        else
                                                free(common_name);
                                }
                        }
                }
        }

        return rc;
}

/* See pqcomm.h comments on OpenSSL implementation of ALPN (RFC 7301) */
static unsigned char alpn_protos[] = PG_ALPN_PROTOCOL_VECTOR;

/*
 *      Create per-connection SSL object, and load the client certificate,
 *      private key, and trusted CA certs.
 *
 *      Returns 0 if OK, -1 on failure (with a message in conn->errorMessage).
 */
static int
initialize_SSL(PGconn *conn)
{
        SSL_CTX    *SSL_context;
        struct stat buf;
        char            homedir[MAXPGPATH];
        char            fnbuf[MAXPGPATH];
        char            sebuf[PG_STRERROR_R_BUFLEN];
        bool            have_homedir;
        bool            have_cert;
        bool            have_rootcert;

        /*
         * We'll need the home directory if any of the relevant parameters are
         * defaulted.  If pqGetHomeDirectory fails, act as though none of the
         * files could be found.
         */
        if (!(conn->sslcert && strlen(conn->sslcert) > 0) ||
                !(conn->sslkey && strlen(conn->sslkey) > 0) ||
                !(conn->sslrootcert && strlen(conn->sslrootcert) > 0) ||
                !((conn->sslcrl && strlen(conn->sslcrl) > 0) ||
                  (conn->sslcrldir && strlen(conn->sslcrldir) > 0)))
                have_homedir = pqGetHomeDirectory(homedir, sizeof(homedir));
        else                                            /* won't need it */
                have_homedir = false;

        /*
         * Create a new SSL_CTX object.
         *
         * We used to share a single SSL_CTX between all connections, but it was
         * complicated if connections used different certificates. So now we
         * create a separate context for each connection, and accept the overhead.
         */
        SSL_context = SSL_CTX_new(SSLv23_method());
        if (!SSL_context)
        {
                char       *err = SSLerrmessage(ERR_get_error());

                libpq_append_conn_error(conn, "could not create SSL context: %s", err);
                SSLerrfree(err);
                return -1;
        }

        /*
         * Delegate the client cert password prompt to the libpq wrapper callback
         * if any is defined.
         *
         * If the application hasn't installed its own and the sslpassword
         * parameter is non-null, we install ours now to make sure we supply
         * PGconn->sslpassword to OpenSSL instead of letting it prompt on stdin.
         *
         * This will replace OpenSSL's default PEM_def_callback (which prompts on
         * stdin), but we're only setting it for this SSL context so it's
         * harmless.
         */
        if (PQsslKeyPassHook
                || (conn->sslpassword && strlen(conn->sslpassword) > 0))
        {
                SSL_CTX_set_default_passwd_cb(SSL_context, PQssl_passwd_cb);
                SSL_CTX_set_default_passwd_cb_userdata(SSL_context, conn);
        }

#ifdef HAVE_SSL_CTX_SET_CERT_CB
        /* Set up a certificate selection callback. */
        SSL_CTX_set_cert_cb(SSL_context, cert_cb, conn);
#endif

        /* Disable old protocol versions */
        SSL_CTX_set_options(SSL_context, SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3);

        /* Set the minimum and maximum protocol versions if necessary */
        if (conn->ssl_min_protocol_version &&
                strlen(conn->ssl_min_protocol_version) != 0)
        {
                int                     ssl_min_ver;

                ssl_min_ver = ssl_protocol_version_to_openssl(conn->ssl_min_protocol_version);

                if (ssl_min_ver == -1)
                {
                        libpq_append_conn_error(conn, "invalid value \"%s\" for minimum SSL protocol version",
                                                                        conn->ssl_min_protocol_version);
                        SSL_CTX_free(SSL_context);
                        return -1;
                }

                if (!SSL_CTX_set_min_proto_version(SSL_context, ssl_min_ver))
                {
                        char       *err = SSLerrmessage(ERR_get_error());

                        libpq_append_conn_error(conn, "could not set minimum SSL protocol version: %s", err);
                        SSLerrfree(err);
                        SSL_CTX_free(SSL_context);
                        return -1;
                }
        }

        if (conn->ssl_max_protocol_version &&
                strlen(conn->ssl_max_protocol_version) != 0)
        {
                int                     ssl_max_ver;

                ssl_max_ver = ssl_protocol_version_to_openssl(conn->ssl_max_protocol_version);

                if (ssl_max_ver == -1)
                {
                        libpq_append_conn_error(conn, "invalid value \"%s\" for maximum SSL protocol version",
                                                                        conn->ssl_max_protocol_version);
                        SSL_CTX_free(SSL_context);
                        return -1;
                }

                if (!SSL_CTX_set_max_proto_version(SSL_context, ssl_max_ver))
                {
                        char       *err = SSLerrmessage(ERR_get_error());

                        libpq_append_conn_error(conn, "could not set maximum SSL protocol version: %s", err);
                        SSLerrfree(err);
                        SSL_CTX_free(SSL_context);
                        return -1;
                }
        }

        /*
         * Disable OpenSSL's moving-write-buffer sanity check, because it causes
         * unnecessary failures in nonblocking send cases.
         */
        SSL_CTX_set_mode(SSL_context, SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER);

        /*
         * If the root cert file exists, load it so we can perform certificate
         * verification. If sslmode is "verify-full" we will also do further
         * verification after the connection has been completed.
         */
        if (conn->sslrootcert && strlen(conn->sslrootcert) > 0)
                strlcpy(fnbuf, conn->sslrootcert, sizeof(fnbuf));
        else if (have_homedir)
                snprintf(fnbuf, sizeof(fnbuf), "%s/%s", homedir, ROOT_CERT_FILE);
        else
                fnbuf[0] = '\0';

        if (strcmp(fnbuf, "system") == 0)
        {
                /*
                 * The "system" sentinel value indicates that we should load whatever
                 * root certificates are installed for use by OpenSSL; these locations
                 * differ by platform. Note that the default system locations may be
                 * further overridden by the SSL_CERT_DIR and SSL_CERT_FILE
                 * environment variables.
                 */
                if (SSL_CTX_set_default_verify_paths(SSL_context) != 1)
                {
                        char       *err = SSLerrmessage(ERR_get_error());

                        libpq_append_conn_error(conn, "could not load system root certificate paths: %s",
                                                                        err);
                        SSLerrfree(err);
                        SSL_CTX_free(SSL_context);
                        return -1;
                }
                have_rootcert = true;
        }
        else if (fnbuf[0] != '\0' &&
                         stat(fnbuf, &buf) == 0)
        {
                X509_STORE *cvstore;

                if (SSL_CTX_load_verify_locations(SSL_context, fnbuf, NULL) != 1)
                {
                        char       *err = SSLerrmessage(ERR_get_error());

                        libpq_append_conn_error(conn, "could not read root certificate file \"%s\": %s",
                                                                        fnbuf, err);
                        SSLerrfree(err);
                        SSL_CTX_free(SSL_context);
                        return -1;
                }

                if ((cvstore = SSL_CTX_get_cert_store(SSL_context)) != NULL)
                {
                        char       *fname = NULL;
                        char       *dname = NULL;

                        if (conn->sslcrl && strlen(conn->sslcrl) > 0)
                                fname = conn->sslcrl;
                        if (conn->sslcrldir && strlen(conn->sslcrldir) > 0)
                                dname = conn->sslcrldir;

                        /* defaults to use the default CRL file */
                        if (!fname && !dname && have_homedir)
                        {
                                snprintf(fnbuf, sizeof(fnbuf), "%s/%s", homedir, ROOT_CRL_FILE);
                                fname = fnbuf;
                        }

                        /* Set the flags to check against the complete CRL chain */
                        if ((fname || dname) &&
                                X509_STORE_load_locations(cvstore, fname, dname) == 1)
                        {
                                X509_STORE_set_flags(cvstore,
                                                                         X509_V_FLAG_CRL_CHECK | X509_V_FLAG_CRL_CHECK_ALL);
                        }

                        /* if not found, silently ignore;  we do not require CRL */
                        ERR_clear_error();
                }
                have_rootcert = true;
        }
        else
        {
                /*
                 * stat() failed; assume root file doesn't exist.  If sslmode is
                 * verify-ca or verify-full, this is an error.  Otherwise, continue
                 * without performing any server cert verification.
                 */
                if (conn->sslmode[0] == 'v')    /* "verify-ca" or "verify-full" */
                {
                        /*
                         * The only way to reach here with an empty filename is if
                         * pqGetHomeDirectory failed.  That's a sufficiently unusual case
                         * that it seems worth having a specialized error message for it.
                         */
                        if (fnbuf[0] == '\0')
                                libpq_append_conn_error(conn, "could not get home directory to locate root certificate file\n"
                                                                                "Either provide the file, use the system's trusted roots with sslrootcert=system, or change sslmode to disable server certificate verification.");
                        else
                                libpq_append_conn_error(conn, "root certificate file \"%s\" does not exist\n"
                                                                                "Either provide the file, use the system's trusted roots with sslrootcert=system, or change sslmode to disable server certificate verification.", fnbuf);
                        SSL_CTX_free(SSL_context);
                        return -1;
                }
                have_rootcert = false;
        }

        /* Read the client certificate file */
        if (conn->sslcert && strlen(conn->sslcert) > 0)
                strlcpy(fnbuf, conn->sslcert, sizeof(fnbuf));
        else if (have_homedir)
                snprintf(fnbuf, sizeof(fnbuf), "%s/%s", homedir, USER_CERT_FILE);
        else
                fnbuf[0] = '\0';

        if (conn->sslcertmode[0] == 'd')        /* disable */
        {
                /* don't send a client cert even if we have one */
                have_cert = false;
        }
        else if (fnbuf[0] == '\0')
        {
                /* no home directory, proceed without a client cert */
                have_cert = false;
        }
        else if (stat(fnbuf, &buf) != 0)
        {
                /*
                 * If file is not present, just go on without a client cert; server
                 * might or might not accept the connection.  Any other error,
                 * however, is grounds for complaint.
                 */
                if (errno != ENOENT && errno != ENOTDIR)
                {
                        libpq_append_conn_error(conn, "could not open certificate file \"%s\": %s",
                                                                        fnbuf, strerror_r(errno, sebuf, sizeof(sebuf)));
                        SSL_CTX_free(SSL_context);
                        return -1;
                }
                have_cert = false;
        }
        else
        {
                /*
                 * Cert file exists, so load it. Since OpenSSL doesn't provide the
                 * equivalent of "SSL_use_certificate_chain_file", we have to load it
                 * into the SSL context, rather than the SSL object.
                 */
                if (SSL_CTX_use_certificate_chain_file(SSL_context, fnbuf) != 1)
                {
                        char       *err = SSLerrmessage(ERR_get_error());

                        libpq_append_conn_error(conn, "could not read certificate file \"%s\": %s",
                                                                        fnbuf, err);
                        SSLerrfree(err);
                        SSL_CTX_free(SSL_context);
                        return -1;
                }

                /* need to load the associated private key, too */
                have_cert = true;
        }

        /*
         * The SSL context is now loaded with the correct root and client
         * certificates. Create a connection-specific SSL object. The private key
         * is loaded directly into the SSL object. (We could load the private key
         * into the context, too, but we have done it this way historically, and
         * it doesn't really matter.)
         */
        if (!(conn->ssl = SSL_new(SSL_context)) ||
                !SSL_set_app_data(conn->ssl, conn) ||
                !ssl_set_pgconn_bio(conn))
        {
                char       *err = SSLerrmessage(ERR_get_error());

                libpq_append_conn_error(conn, "could not establish SSL connection: %s", err);
                SSLerrfree(err);
                SSL_CTX_free(SSL_context);
                return -1;
        }
        conn->ssl_in_use = true;

        /*
         * SSL contexts are reference counted by OpenSSL. We can free it as soon
         * as we have created the SSL object, and it will stick around for as long
         * as it's actually needed.
         */
        SSL_CTX_free(SSL_context);
        SSL_context = NULL;

        /*
         * Set Server Name Indication (SNI), if enabled by connection parameters.
         * Per RFC 6066, do not set it if the host is a literal IP address (IPv4
         * or IPv6).
         */
        if (conn->sslsni && conn->sslsni[0] == '1')
        {
                const char *host = conn->connhost[conn->whichhost].host;

                if (host && host[0] &&
                        !(strspn(host, "0123456789.") == strlen(host) ||
                          strchr(host, ':')))
                {
                        if (SSL_set_tlsext_host_name(conn->ssl, host) != 1)
                        {
                                char       *err = SSLerrmessage(ERR_get_error());

                                libpq_append_conn_error(conn, "could not set SSL Server Name Indication (SNI): %s", err);
                                SSLerrfree(err);
                                return -1;
                        }
                }
        }

        /* Set ALPN */
        {
                int                     retval;

                retval = SSL_set_alpn_protos(conn->ssl, alpn_protos, sizeof(alpn_protos));

                if (retval != 0)
                {
                        char       *err = SSLerrmessage(ERR_get_error());

                        libpq_append_conn_error(conn, "could not set SSL ALPN extension: %s", err);
                        SSLerrfree(err);
                        return -1;
                }
        }

        /*
         * Read the SSL key. If a key is specified, treat it as an engine:key
         * combination if there is colon present - we don't support files with
         * colon in the name. The exception is if the second character is a colon,
         * in which case it can be a Windows filename with drive specification.
         */
        if (have_cert && conn->sslkey && strlen(conn->sslkey) > 0)
        {
#ifdef USE_SSL_ENGINE
                if (strchr(conn->sslkey, ':')
#ifdef WIN32
                        && conn->sslkey[1] != ':'
#endif
                        )
                {
                        /* Colon, but not in second character, treat as engine:key */
                        char       *engine_str = strdup(conn->sslkey);
                        char       *engine_colon;
                        EVP_PKEY   *pkey;

                        if (engine_str == NULL)
                        {
                                libpq_append_conn_error(conn, "out of memory");
                                return -1;
                        }

                        /* cannot return NULL because we already checked before strdup */
                        engine_colon = strchr(engine_str, ':');

                        *engine_colon = '\0';   /* engine_str now has engine name */
                        engine_colon++;         /* engine_colon now has key name */

                        conn->engine = ENGINE_by_id(engine_str);
                        if (conn->engine == NULL)
                        {
                                char       *err = SSLerrmessage(ERR_get_error());

                                libpq_append_conn_error(conn, "could not load SSL engine \"%s\": %s",
                                                                                engine_str, err);
                                SSLerrfree(err);
                                free(engine_str);
                                return -1;
                        }

                        if (ENGINE_init(conn->engine) == 0)
                        {
                                char       *err = SSLerrmessage(ERR_get_error());

                                libpq_append_conn_error(conn, "could not initialize SSL engine \"%s\": %s",
                                                                                engine_str, err);
                                SSLerrfree(err);
                                ENGINE_free(conn->engine);
                                conn->engine = NULL;
                                free(engine_str);
                                return -1;
                        }

                        pkey = ENGINE_load_private_key(conn->engine, engine_colon,
                                                                                   NULL, NULL);
                        if (pkey == NULL)
                        {
                                char       *err = SSLerrmessage(ERR_get_error());

                                libpq_append_conn_error(conn, "could not read private SSL key \"%s\" from engine \"%s\": %s",
                                                                                engine_colon, engine_str, err);
                                SSLerrfree(err);
                                ENGINE_finish(conn->engine);
                                ENGINE_free(conn->engine);
                                conn->engine = NULL;
                                free(engine_str);
                                return -1;
                        }
                        if (SSL_use_PrivateKey(conn->ssl, pkey) != 1)
                        {
                                char       *err = SSLerrmessage(ERR_get_error());

                                libpq_append_conn_error(conn, "could not load private SSL key \"%s\" from engine \"%s\": %s",
                                                                                engine_colon, engine_str, err);
                                SSLerrfree(err);
                                ENGINE_finish(conn->engine);
                                ENGINE_free(conn->engine);
                                conn->engine = NULL;
                                free(engine_str);
                                return -1;
                        }

                        free(engine_str);

                        fnbuf[0] = '\0';        /* indicate we're not going to load from a
                                                                 * file */
                }
                else
#endif                                                  /* USE_SSL_ENGINE */
                {
                        /* PGSSLKEY is not an engine, treat it as a filename */
                        strlcpy(fnbuf, conn->sslkey, sizeof(fnbuf));
                }
        }
        else if (have_homedir)
        {
                /* No PGSSLKEY specified, load default file */
                snprintf(fnbuf, sizeof(fnbuf), "%s/%s", homedir, USER_KEY_FILE);
        }
        else
                fnbuf[0] = '\0';

        if (have_cert && fnbuf[0] != '\0')
        {
                /* read the client key from file */

                if (stat(fnbuf, &buf) != 0)
                {
                        if (errno == ENOENT)
                                libpq_append_conn_error(conn, "certificate present, but not private key file \"%s\"",
                                                                                fnbuf);
                        else
                                libpq_append_conn_error(conn, "could not stat private key file \"%s\": %m",
                                                                                fnbuf);
                        return -1;
                }

                /* Key file must be a regular file */
                if (!S_ISREG(buf.st_mode))
                {
                        libpq_append_conn_error(conn, "private key file \"%s\" is not a regular file",
                                                                        fnbuf);
                        return -1;
                }

                /*
                 * Refuse to load world-readable key files.  We accept root-owned
                 * files with mode 0640 or less, so that we can access system-wide
                 * certificates if we have a supplementary group membership that
                 * allows us to read 'em.  For files with non-root ownership, require
                 * mode 0600 or less.  We need not check the file's ownership exactly;
                 * if we're able to read it despite it having such restrictive
                 * permissions, it must have the right ownership.
                 *
                 * Note: be very careful about tightening these rules.  Some people
                 * expect, for example, that a client process running as root should
                 * be able to use a non-root-owned key file.
                 *
                 * Note that roughly similar checks are performed in
                 * src/backend/libpq/be-secure-common.c so any changes here may need
                 * to be made there as well.  However, this code caters for the case
                 * of current user == root, while that code does not.
                 *
                 * Ideally we would do similar permissions checks on Windows, but it
                 * is not clear how that would work since Unix-style permissions may
                 * not be available.
                 */
#if !defined(WIN32) && !defined(__CYGWIN__)
                if (buf.st_uid == 0 ?
                        buf.st_mode & (S_IWGRP | S_IXGRP | S_IRWXO) :
                        buf.st_mode & (S_IRWXG | S_IRWXO))
                {
                        libpq_append_conn_error(conn,
                                                                        "private key file \"%s\" has group or world access; file must have permissions u=rw (0600) or less if owned by the current user, or permissions u=rw,g=r (0640) or less if owned by root",
                                                                        fnbuf);
                        return -1;
                }
#endif

                if (SSL_use_PrivateKey_file(conn->ssl, fnbuf, SSL_FILETYPE_PEM) != 1)
                {
                        char       *err = SSLerrmessage(ERR_get_error());

                        /*
                         * We'll try to load the file in DER (binary ASN.1) format, and if
                         * that fails too, report the original error. This could mask
                         * issues where there's something wrong with a DER-format cert,
                         * but we'd have to duplicate openssl's format detection to be
                         * smarter than this. We can't just probe for a leading -----BEGIN
                         * because PEM can have leading non-matching lines and blanks.
                         * OpenSSL doesn't expose its get_name(...) and its PEM routines
                         * don't differentiate between failure modes in enough detail to
                         * let us tell the difference between "not PEM, try DER" and
                         * "wrong password".
                         */
                        if (SSL_use_PrivateKey_file(conn->ssl, fnbuf, SSL_FILETYPE_ASN1) != 1)
                        {
                                libpq_append_conn_error(conn, "could not load private key file \"%s\": %s",
                                                                                fnbuf, err);
                                SSLerrfree(err);
                                return -1;
                        }

                        SSLerrfree(err);
                }
        }

        /* verify that the cert and key go together */
        if (have_cert &&
                SSL_check_private_key(conn->ssl) != 1)
        {
                char       *err = SSLerrmessage(ERR_get_error());

                libpq_append_conn_error(conn, "certificate does not match private key file \"%s\": %s",
                                                                fnbuf, err);
                SSLerrfree(err);
                return -1;
        }

        /*
         * If a root cert was loaded, also set our certificate verification
         * callback.
         */
        if (have_rootcert)
                SSL_set_verify(conn->ssl, SSL_VERIFY_PEER, verify_cb);

        /*
         * Set compression option if necessary.
         */
        if (conn->sslcompression && conn->sslcompression[0] == '0')
                SSL_set_options(conn->ssl, SSL_OP_NO_COMPRESSION);
        else
                SSL_clear_options(conn->ssl, SSL_OP_NO_COMPRESSION);

        return 0;
}

/*
 *      Attempt to negotiate SSL connection.
 */
static PostgresPollingStatusType
open_client_SSL(PGconn *conn)
{
        int                     r;

        SOCK_ERRNO_SET(0);
        ERR_clear_error();
        r = SSL_connect(conn->ssl);
        if (r <= 0)
        {
                int                     save_errno = SOCK_ERRNO;
                int                     err = SSL_get_error(conn->ssl, r);
                unsigned long ecode;

                ecode = ERR_get_error();
                switch (err)
                {
                        case SSL_ERROR_WANT_READ:
                                return PGRES_POLLING_READING;

                        case SSL_ERROR_WANT_WRITE:
                                return PGRES_POLLING_WRITING;

                        case SSL_ERROR_SYSCALL:
                                {
                                        char            sebuf[PG_STRERROR_R_BUFLEN];
                                        unsigned long vcode;

                                        vcode = SSL_get_verify_result(conn->ssl);

                                        /*
                                         * If we get an X509 error here for failing to load the
                                         * local issuer cert, without an error in the socket layer
                                         * it means that verification failed due to a missing
                                         * system CA pool without it being a protocol error. We
                                         * inspect the sslrootcert setting to ensure that the user
                                         * was using the system CA pool. For other errors, log
                                         * them using the normal SYSCALL logging.
                                         */
                                        if (save_errno == 0 &&
                                                vcode == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY &&
                                                strcmp(conn->sslrootcert, "system") == 0)
                                                libpq_append_conn_error(conn, "SSL error: certificate verify failed: %s",
                                                                                                X509_verify_cert_error_string(vcode));
                                        else if (r == -1 && save_errno != 0)
                                                libpq_append_conn_error(conn, "SSL SYSCALL error: %s",
                                                                                                SOCK_STRERROR(save_errno, sebuf, sizeof(sebuf)));
                                        else
                                                libpq_append_conn_error(conn, "SSL SYSCALL error: EOF detected");
                                        pgtls_close(conn);
                                        return PGRES_POLLING_FAILED;
                                }
                        case SSL_ERROR_SSL:
                                {
                                        char       *err = SSLerrmessage(ecode);

                                        libpq_append_conn_error(conn, "SSL error: %s", err);
                                        SSLerrfree(err);
                                        switch (ERR_GET_REASON(ecode))
                                        {
                                                        /*
                                                         * UNSUPPORTED_PROTOCOL, WRONG_VERSION_NUMBER, and
                                                         * TLSV1_ALERT_PROTOCOL_VERSION have been observed
                                                         * when trying to communicate with an old OpenSSL
                                                         * library, or when the client and server specify
                                                         * disjoint protocol ranges.
                                                         * NO_PROTOCOLS_AVAILABLE occurs if there's a
                                                         * local misconfiguration (which can happen
                                                         * despite our checks, if openssl.cnf injects a
                                                         * limit we didn't account for).  It's not very
                                                         * clear what would make OpenSSL return the other
                                                         * codes listed here, but a hint about protocol
                                                         * versions seems like it's appropriate for all.
                                                         */
                                                case SSL_R_NO_PROTOCOLS_AVAILABLE:
                                                case SSL_R_UNSUPPORTED_PROTOCOL:
                                                case SSL_R_BAD_PROTOCOL_VERSION_NUMBER:
                                                case SSL_R_UNKNOWN_PROTOCOL:
                                                case SSL_R_UNKNOWN_SSL_VERSION:
                                                case SSL_R_UNSUPPORTED_SSL_VERSION:
                                                case SSL_R_WRONG_SSL_VERSION:
                                                case SSL_R_WRONG_VERSION_NUMBER:
                                                case SSL_R_TLSV1_ALERT_PROTOCOL_VERSION:
#ifdef SSL_R_VERSION_TOO_HIGH
                                                case SSL_R_VERSION_TOO_HIGH:
                                                case SSL_R_VERSION_TOO_LOW:
#endif
                                                        libpq_append_conn_error(conn, "This may indicate that the server does not support any SSL protocol version between %s and %s.",
                                                                                                        conn->ssl_min_protocol_version ?
                                                                                                        conn->ssl_min_protocol_version :
                                                                                                        MIN_OPENSSL_TLS_VERSION,
                                                                                                        conn->ssl_max_protocol_version ?
                                                                                                        conn->ssl_max_protocol_version :
                                                                                                        MAX_OPENSSL_TLS_VERSION);
                                                        break;
                                                default:
                                                        break;
                                        }
                                        pgtls_close(conn);
                                        return PGRES_POLLING_FAILED;
                                }

                        default:
                                libpq_append_conn_error(conn, "unrecognized SSL error code: %d", err);
                                pgtls_close(conn);
                                return PGRES_POLLING_FAILED;
                }
        }

        /* ALPN is mandatory with direct SSL connections */
        if (conn->current_enc_method == ENC_SSL && conn->sslnegotiation[0] == 'd')
        {
                const unsigned char *selected;
                unsigned int len;

                SSL_get0_alpn_selected(conn->ssl, &selected, &len);

                if (selected == NULL)
                {
                        libpq_append_conn_error(conn, "direct SSL connection was established without ALPN protocol negotiation extension");
                        pgtls_close(conn);
                        return PGRES_POLLING_FAILED;
                }

                /*
                 * We only support one protocol so that's what the negotiation should
                 * always choose, but doesn't hurt to check.
                 */
                if (len != strlen(PG_ALPN_PROTOCOL) ||
                        memcmp(selected, PG_ALPN_PROTOCOL, strlen(PG_ALPN_PROTOCOL)) != 0)
                {
                        libpq_append_conn_error(conn, "SSL connection was established with unexpected ALPN protocol");
                        pgtls_close(conn);
                        return PGRES_POLLING_FAILED;
                }
        }

        /*
         * We already checked the server certificate in initialize_SSL() using
         * SSL_CTX_set_verify(), if root.crt exists.
         */

        /* get server certificate */
        conn->peer = SSL_get_peer_certificate(conn->ssl);
        if (conn->peer == NULL)
        {
                char       *err = SSLerrmessage(ERR_get_error());

                libpq_append_conn_error(conn, "certificate could not be obtained: %s", err);
                SSLerrfree(err);
                pgtls_close(conn);
                return PGRES_POLLING_FAILED;
        }

        if (!pq_verify_peer_name_matches_certificate(conn))
        {
                pgtls_close(conn);
                return PGRES_POLLING_FAILED;
        }

        /* SSL handshake is complete */
        return PGRES_POLLING_OK;
}

void
pgtls_close(PGconn *conn)
{
        if (conn->ssl_in_use)
        {
                if (conn->ssl)
                {
                        /*
                         * We can't destroy everything SSL-related here due to the
                         * possible later calls to OpenSSL routines which may need our
                         * thread callbacks, so set a flag here and check at the end.
                         */

                        SSL_shutdown(conn->ssl);
                        SSL_free(conn->ssl);
                        conn->ssl = NULL;
                        conn->ssl_in_use = false;
                        conn->ssl_handshake_started = false;
                }

                if (conn->peer)
                {
                        X509_free(conn->peer);
                        conn->peer = NULL;
                }

#ifdef USE_SSL_ENGINE
                if (conn->engine)
                {
                        ENGINE_finish(conn->engine);
                        ENGINE_free(conn->engine);
                        conn->engine = NULL;
                }
#endif
        }
}


/*
 * Obtain reason string for passed SSL errcode
 *
 * ERR_get_error() is used by caller to get errcode to pass here.
 * The result must be freed after use, using SSLerrfree.
 *
 * Some caution is needed here since ERR_reason_error_string will return NULL
 * if it doesn't recognize the error code, or (in OpenSSL >= 3) if the code
 * represents a system errno value.  We don't want to return NULL ever.
 */
static char ssl_nomem[] = "out of memory allocating error description";

#define SSL_ERR_LEN 128

static char *
SSLerrmessage(unsigned long ecode)
{
        const char *errreason;
        char       *errbuf;

        errbuf = malloc(SSL_ERR_LEN);
        if (!errbuf)
                return ssl_nomem;
        if (ecode == 0)
        {
                snprintf(errbuf, SSL_ERR_LEN, libpq_gettext("no SSL error reported"));
                return errbuf;
        }
        errreason = ERR_reason_error_string(ecode);
        if (errreason != NULL)
        {
                strlcpy(errbuf, errreason, SSL_ERR_LEN);
                return errbuf;
        }

        /*
         * Server aborted the connection with TLS "no_application_protocol" alert.
         * The ERR_reason_error_string() function doesn't give any error string
         * for that for some reason, so do it ourselves.  See
         * https://github.com/openssl/openssl/issues/24300.  This is available in
         * OpenSSL 1.1.0 and later, as well as in LibreSSL 3.4.3 (OpenBSD 7.0) and
         * later.
         */
#ifdef SSL_AD_NO_APPLICATION_PROTOCOL
        if (ERR_GET_LIB(ecode) == ERR_LIB_SSL &&
                ERR_GET_REASON(ecode) == SSL_AD_REASON_OFFSET + SSL_AD_NO_APPLICATION_PROTOCOL)
        {
                snprintf(errbuf, SSL_ERR_LEN, "no application protocol");
                return errbuf;
        }
#endif

        /*
         * In OpenSSL 3.0.0 and later, ERR_reason_error_string does not map system
         * errno values anymore.  (See OpenSSL source code for the explanation.)
         * We can cover that shortcoming with this bit of code.  Older OpenSSL
         * versions don't have the ERR_SYSTEM_ERROR macro, but that's okay because
         * they don't have the shortcoming either.
         */
#ifdef ERR_SYSTEM_ERROR
        if (ERR_SYSTEM_ERROR(ecode))
        {
                strerror_r(ERR_GET_REASON(ecode), errbuf, SSL_ERR_LEN);
                return errbuf;
        }
#endif

        /* No choice but to report the numeric ecode */
        snprintf(errbuf, SSL_ERR_LEN, libpq_gettext("SSL error code %lu"), ecode);
        return errbuf;
}

static void
SSLerrfree(char *buf)
{
        if (buf != ssl_nomem)
                free(buf);
}

/* ------------------------------------------------------------ */
/*                                      SSL information functions                                       */
/* ------------------------------------------------------------ */

/*
 *      Return pointer to OpenSSL object.
 */
void *
PQgetssl(PGconn *conn)
{
        if (!conn)
                return NULL;
        return conn->ssl;
}

void *
PQsslStruct(PGconn *conn, const char *struct_name)
{
        if (!conn)
                return NULL;
        if (strcmp(struct_name, "OpenSSL") == 0)
                return conn->ssl;
        return NULL;
}

const char *const *
PQsslAttributeNames(PGconn *conn)
{
        static const char *const openssl_attrs[] = {
                "library",
                "key_bits",
                "cipher",
                "compression",
                "protocol",
                "alpn",
                NULL
        };
        static const char *const empty_attrs[] = {NULL};

        if (!conn)
        {
                /* Return attributes of default SSL library */
                return openssl_attrs;
        }

        /* No attrs for unencrypted connection */
        if (conn->ssl == NULL)
                return empty_attrs;

        return openssl_attrs;
}

const char *
PQsslAttribute(PGconn *conn, const char *attribute_name)
{
        if (!conn)
        {
                /* PQsslAttribute(NULL, "library") reports the default SSL library */
                if (strcmp(attribute_name, "library") == 0)
                        return "OpenSSL";
                return NULL;
        }

        /* All attributes read as NULL for a non-encrypted connection */
        if (conn->ssl == NULL)
                return NULL;

        if (strcmp(attribute_name, "library") == 0)
                return "OpenSSL";

        if (strcmp(attribute_name, "key_bits") == 0)
        {
                static char sslbits_str[12];
                int                     sslbits;

                SSL_get_cipher_bits(conn->ssl, &sslbits);
                snprintf(sslbits_str, sizeof(sslbits_str), "%d", sslbits);
                return sslbits_str;
        }

        if (strcmp(attribute_name, "cipher") == 0)
                return SSL_get_cipher(conn->ssl);

        if (strcmp(attribute_name, "compression") == 0)
                return SSL_get_current_compression(conn->ssl) ? "on" : "off";

        if (strcmp(attribute_name, "protocol") == 0)
                return SSL_get_version(conn->ssl);

        if (strcmp(attribute_name, "alpn") == 0)
        {
                const unsigned char *data;
                unsigned int len;
                static char alpn_str[256];      /* alpn doesn't support longer than 255
                                                                         * bytes */

                SSL_get0_alpn_selected(conn->ssl, &data, &len);
                if (data == NULL || len == 0 || len > sizeof(alpn_str) - 1)
                        return "";
                memcpy(alpn_str, data, len);
                alpn_str[len] = 0;
                return alpn_str;
        }

        return NULL;                            /* unknown attribute */
}

/*
 * Private substitute BIO: this does the sending and receiving using
 * pqsecure_raw_write() and pqsecure_raw_read() instead, to allow those
 * functions to disable SIGPIPE and give better error messages on I/O errors.
 *
 * These functions are closely modelled on the standard socket BIO in OpenSSL;
 * see sock_read() and sock_write() in OpenSSL's crypto/bio/bss_sock.c.
 */

/* protected by ssl_config_mutex */
static BIO_METHOD *pgconn_bio_method_ptr;

static int
pgconn_bio_read(BIO *h, char *buf, int size)
{
        PGconn     *conn = (PGconn *) BIO_get_data(h);
        int                     res;

        res = pqsecure_raw_read(conn, buf, size);
        BIO_clear_retry_flags(h);
        conn->last_read_was_eof = res == 0;
        if (res < 0)
        {
                /* If we were interrupted, tell caller to retry */
                switch (SOCK_ERRNO)
                {
#ifdef EAGAIN
                        case EAGAIN:
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
                        case EWOULDBLOCK:
#endif
                        case EINTR:
                                BIO_set_retry_read(h);
                                break;

                        default:
                                break;
                }
        }

        if (res > 0)
                conn->ssl_handshake_started = true;

        return res;
}

static int
pgconn_bio_write(BIO *h, const char *buf, int size)
{
        int                     res;

        res = pqsecure_raw_write((PGconn *) BIO_get_data(h), buf, size);
        BIO_clear_retry_flags(h);
        if (res < 0)
        {
                /* If we were interrupted, tell caller to retry */
                switch (SOCK_ERRNO)
                {
#ifdef EAGAIN
                        case EAGAIN:
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
                        case EWOULDBLOCK:
#endif
                        case EINTR:
                                BIO_set_retry_write(h);
                                break;

                        default:
                                break;
                }
        }

        return res;
}

static long
pgconn_bio_ctrl(BIO *h, int cmd, long num, void *ptr)
{
        long            res;
        PGconn     *conn = (PGconn *) BIO_get_data(h);

        switch (cmd)
        {
                case BIO_CTRL_EOF:

                        /*
                         * This should not be needed. pgconn_bio_read already has a way to
                         * signal EOF to OpenSSL. However, OpenSSL made an undocumented,
                         * backwards-incompatible change and now expects EOF via BIO_ctrl.
                         * See https://github.com/openssl/openssl/issues/8208
                         */
                        res = conn->last_read_was_eof;
                        break;
                case BIO_CTRL_FLUSH:
                        /* libssl expects all BIOs to support BIO_flush. */
                        res = 1;
                        break;
                default:
                        res = 0;
                        break;
        }

        return res;
}

static BIO_METHOD *
pgconn_bio_method(void)
{
        BIO_METHOD *res;

        if (pthread_mutex_lock(&ssl_config_mutex))
                return NULL;

        res = pgconn_bio_method_ptr;

        if (!pgconn_bio_method_ptr)
        {
                int                     my_bio_index;

                my_bio_index = BIO_get_new_index();
                if (my_bio_index == -1)
                        goto err;
                my_bio_index |= BIO_TYPE_SOURCE_SINK;
                res = BIO_meth_new(my_bio_index, "libpq socket");
                if (!res)
                        goto err;

                /*
                 * As of this writing, these functions never fail. But check anyway,
                 * like OpenSSL's own examples do.
                 */
                if (!BIO_meth_set_write(res, pgconn_bio_write) ||
                        !BIO_meth_set_read(res, pgconn_bio_read) ||
                        !BIO_meth_set_ctrl(res, pgconn_bio_ctrl))
                {
                        goto err;
                }
        }

        pgconn_bio_method_ptr = res;
        pthread_mutex_unlock(&ssl_config_mutex);
        return res;

err:
        if (res)
                BIO_meth_free(res);
        pthread_mutex_unlock(&ssl_config_mutex);
        return NULL;
}

static int
ssl_set_pgconn_bio(PGconn *conn)
{
        BIO                *bio;
        BIO_METHOD *bio_method;

        bio_method = pgconn_bio_method();
        if (bio_method == NULL)
                return 0;

        bio = BIO_new(bio_method);
        if (bio == NULL)
                return 0;

        BIO_set_data(bio, conn);
        BIO_set_init(bio, 1);

        SSL_set_bio(conn->ssl, bio, bio);
        return 1;
}

/*
 * This is the default handler to return a client cert password from
 * conn->sslpassword. Apps may install it explicitly if they want to
 * prevent openssl from ever prompting on stdin.
 */
int
PQdefaultSSLKeyPassHook_OpenSSL(char *buf, int size, PGconn *conn)
{
        if (conn && conn->sslpassword)
        {
                if (strlen(conn->sslpassword) + 1 > size)
                        fprintf(stderr, libpq_gettext("WARNING: sslpassword truncated\n"));
                strncpy(buf, conn->sslpassword, size);
                buf[size - 1] = '\0';
                return strlen(buf);
        }
        else
        {
                buf[0] = '\0';
                return 0;
        }
}

PQsslKeyPassHook_OpenSSL_type
PQgetSSLKeyPassHook_OpenSSL(void)
{
        return PQsslKeyPassHook;
}

void
PQsetSSLKeyPassHook_OpenSSL(PQsslKeyPassHook_OpenSSL_type hook)
{
        PQsslKeyPassHook = hook;
}

/*
 * Supply a password to decrypt a client certificate.
 *
 * This must match OpenSSL type pem_password_cb.
 */
static int
PQssl_passwd_cb(char *buf, int size, int rwflag, void *userdata)
{
        PGconn     *conn = userdata;

        if (PQsslKeyPassHook)
                return PQsslKeyPassHook(buf, size, conn);
        else
                return PQdefaultSSLKeyPassHook_OpenSSL(buf, size, conn);
}

/*
 * Convert TLS protocol version string to OpenSSL values
 *
 * If a version is passed that is not supported by the current OpenSSL version,
 * then we return -1. If a non-negative value is returned, subsequent code can
 * assume it is working with a supported version.
 *
 * Note: this is rather similar to the backend routine in be-secure-openssl.c,
 * so make sure to update both routines if changing this one.
 */
static int
ssl_protocol_version_to_openssl(const char *protocol)
{
        if (pg_strcasecmp("TLSv1", protocol) == 0)
                return TLS1_VERSION;

#ifdef TLS1_1_VERSION
        if (pg_strcasecmp("TLSv1.1", protocol) == 0)
                return TLS1_1_VERSION;
#endif

#ifdef TLS1_2_VERSION
        if (pg_strcasecmp("TLSv1.2", protocol) == 0)
                return TLS1_2_VERSION;
#endif

#ifdef TLS1_3_VERSION
        if (pg_strcasecmp("TLSv1.3", protocol) == 0)
                return TLS1_3_VERSION;
#endif

        return -1;
}