entropy.c

   1 /*
   2  * Copyright (c) 2001 Damien Miller.  All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  23  */
  24
  25 #include "includes.h"
  26
  27 #include <sys/types.h>
  28 #include <sys/wait.h>
  29
  30 #ifdef HAVE_SYS_STAT_H
  31 # include <sys/stat.h>
  32 #endif
  33
  34 #ifdef HAVE_FCNTL_H
  35 # include <fcntl.h>
  36 #endif
  37 #include <stdarg.h>
  38 #include <string.h>
  39 #include <signal.h>
  40 #include <unistd.h>
  41
  42 #include <openssl/rand.h>
  43 #include <openssl/crypto.h>
  44 #include <openssl/err.h>
  45
  46 #include "ssh.h"
  47 #include "misc.h"
  48 #include "xmalloc.h"
  49 #include "atomicio.h"
  50 #include "pathnames.h"
  51 #include "log.h"
  52 #include "buffer.h"
  53
  54 /*
  55  * Portable OpenSSH PRNG seeding:
  56  * If OpenSSL has not "internally seeded" itself (e.g. pulled data from
  57  * /dev/random), then we execute a "ssh-rand-helper" program which
  58  * collects entropy and writes it to stdout. The child program must
  59  * write at least RANDOM_SEED_SIZE bytes. The child is run with stderr
  60  * attached, so error/debugging output should be visible.
  61  *
  62  * XXX: we should tell the child how many bytes we need.
  63  */
  64
  65 #ifndef OPENSSL_PRNG_ONLY
  66 #define RANDOM_SEED_SIZE 48
  67 static uid_t original_uid, original_euid;
  68 #endif
  69
  70 void
  71 seed_rng(void)
  72 {
  73 #ifndef OPENSSL_PRNG_ONLY
  74         int devnull;
  75         int p[2];
  76         pid_t pid;
  77         int ret;
  78         unsigned char buf[RANDOM_SEED_SIZE];
  79         mysig_t old_sigchld;
  80
  81         if (RAND_status() == 1) {
  82                 debug3("RNG is ready, skipping seeding");
  83                 return;
  84         }
  85
  86         debug3("Seeding PRNG from %s", SSH_RAND_HELPER);
  87
  88         if ((devnull = open("/dev/null", O_RDWR)) == -1)
  89                 fatal("Couldn't open /dev/null: %s", strerror(errno));
  90         if (pipe(p) == -1)
  91                 fatal("pipe: %s", strerror(errno));
  92
  93         old_sigchld = signal(SIGCHLD, SIG_DFL);
  94         if ((pid = fork()) == -1)
  95                 fatal("Couldn't fork: %s", strerror(errno));
  96         if (pid == 0) {
  97                 dup2(devnull, STDIN_FILENO);
  98                 dup2(p[1], STDOUT_FILENO);
  99                 /* Keep stderr open for errors */
 100                 close(p[0]);
 101                 close(p[1]);
 102                 close(devnull);
 103
 104                 if (original_uid != original_euid &&
 105                     ( seteuid(getuid()) == -1 ||
 106                       setuid(original_uid) == -1) ) {
 107                         fprintf(stderr, "(rand child) setuid(%li): %s\n",
 108                             (long int)original_uid, strerror(errno));
 109                         _exit(1);
 110                 }
 111
 112                 execl(SSH_RAND_HELPER, "ssh-rand-helper", NULL);
 113                 fprintf(stderr, "(rand child) Couldn't exec '%s': %s\n",
 114                     SSH_RAND_HELPER, strerror(errno));
 115                 _exit(1);
 116         }
 117
 118         close(devnull);
 119         close(p[1]);
 120
 121         memset(buf, '\0', sizeof(buf));
 122         ret = atomicio(read, p[0], buf, sizeof(buf));
 123         if (ret == -1)
 124                 fatal("Couldn't read from ssh-rand-helper: %s",
 125                     strerror(errno));
 126         if (ret != sizeof(buf))
 127                 fatal("ssh-rand-helper child produced insufficient data");
 128
 129         close(p[0]);
 130
 131         if (waitpid(pid, &ret, 0) == -1)
 132                 fatal("Couldn't wait for ssh-rand-helper completion: %s",
 133                     strerror(errno));
 134         signal(SIGCHLD, old_sigchld);
 135
 136         /* We don't mind if the child exits upon a SIGPIPE */
 137         if (!WIFEXITED(ret) &&
 138             (!WIFSIGNALED(ret) || WTERMSIG(ret) != SIGPIPE))
 139                 fatal("ssh-rand-helper terminated abnormally");
 140         if (WEXITSTATUS(ret) != 0)
 141                 fatal("ssh-rand-helper exit with exit status %d", ret);
 142
 143         RAND_add(buf, sizeof(buf), sizeof(buf));
 144         memset(buf, '\0', sizeof(buf));
 145
 146 #endif /* OPENSSL_PRNG_ONLY */
 147         if (RAND_status() != 1)
 148                 fatal("PRNG is not seeded");
 149 }
 150
 151 void
 152 init_rng(void)
 153 {
 154         /*
 155          * OpenSSL version numbers: MNNFFPPS: major minor fix patch status
 156          * We match major, minor, fix and status (not patch)
 157          */
 158         if ((SSLeay() ^ OPENSSL_VERSION_NUMBER) & ~0xff0L)
 159                 fatal("OpenSSL version mismatch. Built against %lx, you "
 160                     "have %lx", (u_long)OPENSSL_VERSION_NUMBER, SSLeay());
 161
 162 #ifndef OPENSSL_PRNG_ONLY
 163         original_uid = getuid();
 164         original_euid = geteuid();
 165 #endif
 166 }
 167
 168 #ifndef OPENSSL_PRNG_ONLY
 169 void
 170 rexec_send_rng_seed(Buffer *m)
 171 {
 172         u_char buf[RANDOM_SEED_SIZE];
 173
 174         if (RAND_bytes(buf, sizeof(buf)) <= 0) {
 175                 error("Couldn't obtain random bytes (error %ld)",
 176                     ERR_get_error());
 177                 buffer_put_string(m, "", 0);
 178         } else
 179                 buffer_put_string(m, buf, sizeof(buf));
 180 }
 181
 182 void
 183 rexec_recv_rng_seed(Buffer *m)
 184 {
 185         u_char *buf;
 186         u_int len;
 187
 188         buf = buffer_get_string_ret(m, &len);
 189         if (buf != NULL) {
 190                 debug3("rexec_recv_rng_seed: seeding rng with %u bytes", len);
 191                 RAND_add(buf, len, len);
 192         }
 193 }
 194 #endif