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 <unistd.h>
  38
  39 #include <openssl/rand.h>
  40 #include <openssl/crypto.h>
  41 #include <openssl/err.h>
  42
  43 #include "ssh.h"
  44 #include "misc.h"
  45 #include "xmalloc.h"
  46 #include "atomicio.h"
  47 #include "pathnames.h"
  48 #include "log.h"
  49 #include "buffer.h"
  50
  51 /*
  52  * Portable OpenSSH PRNG seeding:
  53  * If OpenSSL has not "internally seeded" itself (e.g. pulled data from
  54  * /dev/random), then we execute a "ssh-rand-helper" program which
  55  * collects entropy and writes it to stdout. The child program must
  56  * write at least RANDOM_SEED_SIZE bytes. The child is run with stderr
  57  * attached, so error/debugging output should be visible.
  58  *
  59  * XXX: we should tell the child how many bytes we need.
  60  */
  61
  62 #ifndef OPENSSL_PRNG_ONLY
  63 #define RANDOM_SEED_SIZE 48
  64 static uid_t original_uid, original_euid;
  65 #endif
  66
  67 void
  68 seed_rng(void)
  69 {
  70 #ifndef OPENSSL_PRNG_ONLY
  71         int devnull;
  72         int p[2];
  73         pid_t pid;
  74         int ret;
  75         unsigned char buf[RANDOM_SEED_SIZE];
  76         mysig_t old_sigchld;
  77
  78         if (RAND_status() == 1) {
  79                 debug3("RNG is ready, skipping seeding");
  80                 return;
  81         }
  82
  83         debug3("Seeding PRNG from %s", SSH_RAND_HELPER);
  84
  85         if ((devnull = open("/dev/null", O_RDWR)) == -1)
  86                 fatal("Couldn't open /dev/null: %s", strerror(errno));
  87         if (pipe(p) == -1)
  88                 fatal("pipe: %s", strerror(errno));
  89
  90         old_sigchld = signal(SIGCHLD, SIG_DFL);
  91         if ((pid = fork()) == -1)
  92                 fatal("Couldn't fork: %s", strerror(errno));
  93         if (pid == 0) {
  94                 dup2(devnull, STDIN_FILENO);
  95                 dup2(p[1], STDOUT_FILENO);
  96                 /* Keep stderr open for errors */
  97                 close(p[0]);
  98                 close(p[1]);
  99                 close(devnull);
 100
 101                 if (original_uid != original_euid &&
 102                     ( seteuid(getuid()) == -1 ||
 103                       setuid(original_uid) == -1) ) {
 104                         fprintf(stderr, "(rand child) setuid(%li): %s\n",
 105                             (long int)original_uid, strerror(errno));
 106                         _exit(1);
 107                 }
 108
 109                 execl(SSH_RAND_HELPER, "ssh-rand-helper", NULL);
 110                 fprintf(stderr, "(rand child) Couldn't exec '%s': %s\n",
 111                     SSH_RAND_HELPER, strerror(errno));
 112                 _exit(1);
 113         }
 114
 115         close(devnull);
 116         close(p[1]);
 117
 118         memset(buf, '\0', sizeof(buf));
 119         ret = atomicio(read, p[0], buf, sizeof(buf));
 120         if (ret == -1)
 121                 fatal("Couldn't read from ssh-rand-helper: %s",
 122                     strerror(errno));
 123         if (ret != sizeof(buf))
 124                 fatal("ssh-rand-helper child produced insufficient data");
 125
 126         close(p[0]);
 127
 128         if (waitpid(pid, &ret, 0) == -1)
 129                 fatal("Couldn't wait for ssh-rand-helper completion: %s",
 130                     strerror(errno));
 131         signal(SIGCHLD, old_sigchld);
 132
 133         /* We don't mind if the child exits upon a SIGPIPE */
 134         if (!WIFEXITED(ret) &&
 135             (!WIFSIGNALED(ret) || WTERMSIG(ret) != SIGPIPE))
 136                 fatal("ssh-rand-helper terminated abnormally");
 137         if (WEXITSTATUS(ret) != 0)
 138                 fatal("ssh-rand-helper exit with exit status %d", ret);
 139
 140         RAND_add(buf, sizeof(buf), sizeof(buf));
 141         memset(buf, '\0', sizeof(buf));
 142
 143 #endif /* OPENSSL_PRNG_ONLY */
 144         if (RAND_status() != 1)
 145                 fatal("PRNG is not seeded");
 146 }
 147
 148 void
 149 init_rng(void)
 150 {
 151         /*
 152          * OpenSSL version numbers: MNNFFPPS: major minor fix patch status
 153          * We match major, minor, fix and status (not patch)
 154          */
 155         if ((SSLeay() ^ OPENSSL_VERSION_NUMBER) & ~0xff0L)
 156                 fatal("OpenSSL version mismatch. Built against %lx, you "
 157                     "have %lx", OPENSSL_VERSION_NUMBER, SSLeay());
 158
 159 #ifndef OPENSSL_PRNG_ONLY
 160         original_uid = getuid();
 161         original_euid = geteuid();
 162 #endif
 163 }
 164
 165 #ifndef OPENSSL_PRNG_ONLY
 166 void
 167 rexec_send_rng_seed(Buffer *m)
 168 {
 169         u_char buf[RANDOM_SEED_SIZE];
 170
 171         if (RAND_bytes(buf, sizeof(buf)) <= 0) {
 172                 error("Couldn't obtain random bytes (error %ld)",
 173                     ERR_get_error());
 174                 buffer_put_string(m, "", 0);
 175         } else
 176                 buffer_put_string(m, buf, sizeof(buf));
 177 }
 178
 179 void
 180 rexec_recv_rng_seed(Buffer *m)
 181 {
 182         u_char *buf;
 183         u_int len;
 184
 185         buf = buffer_get_string_ret(m, &len);
 186         if (buf != NULL) {
 187                 debug3("rexec_recv_rng_seed: seeding rng with %u bytes", len);
 188                 RAND_add(buf, len, len);
 189         }
 190 }
 191 #endif