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 #include <openssl/rand.h>
  31 #include <openssl/crypto.h>
  32 #include <openssl/err.h>
  33
  34 #include "ssh.h"
  35 #include "misc.h"
  36 #include "xmalloc.h"
  37 #include "atomicio.h"
  38 #include "pathnames.h"
  39 #include "log.h"
  40 #include "buffer.h"
  41 #include "bufaux.h"
  42
  43 /*
  44  * Portable OpenSSH PRNG seeding:
  45  * If OpenSSL has not "internally seeded" itself (e.g. pulled data from
  46  * /dev/random), then we execute a "ssh-rand-helper" program which
  47  * collects entropy and writes it to stdout. The child program must
  48  * write at least RANDOM_SEED_SIZE bytes. The child is run with stderr
  49  * attached, so error/debugging output should be visible.
  50  *
  51  * XXX: we should tell the child how many bytes we need.
  52  */
  53
  54 #ifndef OPENSSL_PRNG_ONLY
  55 #define RANDOM_SEED_SIZE 48
  56 static uid_t original_uid, original_euid;
  57 #endif
  58
  59 void
  60 seed_rng(void)
  61 {
  62 #ifndef OPENSSL_PRNG_ONLY
  63         int devnull;
  64         int p[2];
  65         pid_t pid;
  66         int ret;
  67         unsigned char buf[RANDOM_SEED_SIZE];
  68         mysig_t old_sigchld;
  69
  70         if (RAND_status() == 1) {
  71                 debug3("RNG is ready, skipping seeding");
  72                 return;
  73         }
  74
  75         debug3("Seeding PRNG from %s", SSH_RAND_HELPER);
  76
  77         if ((devnull = open("/dev/null", O_RDWR)) == -1)
  78                 fatal("Couldn't open /dev/null: %s", strerror(errno));
  79         if (pipe(p) == -1)
  80                 fatal("pipe: %s", strerror(errno));
  81
  82         old_sigchld = signal(SIGCHLD, SIG_DFL);
  83         if ((pid = fork()) == -1)
  84                 fatal("Couldn't fork: %s", strerror(errno));
  85         if (pid == 0) {
  86                 dup2(devnull, STDIN_FILENO);
  87                 dup2(p[1], STDOUT_FILENO);
  88                 /* Keep stderr open for errors */
  89                 close(p[0]);
  90                 close(p[1]);
  91                 close(devnull);
  92
  93                 if (original_uid != original_euid &&
  94                     ( seteuid(getuid()) == -1 ||
  95                       setuid(original_uid) == -1) ) {
  96                         fprintf(stderr, "(rand child) setuid(%li): %s\n",
  97                             (long int)original_uid, strerror(errno));
  98                         _exit(1);
  99                 }
 100
 101                 execl(SSH_RAND_HELPER, "ssh-rand-helper", NULL);
 102                 fprintf(stderr, "(rand child) Couldn't exec '%s': %s\n",
 103                     SSH_RAND_HELPER, strerror(errno));
 104                 _exit(1);
 105         }
 106
 107         close(devnull);
 108         close(p[1]);
 109
 110         memset(buf, '\0', sizeof(buf));
 111         ret = atomicio(read, p[0], buf, sizeof(buf));
 112         if (ret == -1)
 113                 fatal("Couldn't read from ssh-rand-helper: %s",
 114                     strerror(errno));
 115         if (ret != sizeof(buf))
 116                 fatal("ssh-rand-helper child produced insufficient data");
 117
 118         close(p[0]);
 119
 120         if (waitpid(pid, &ret, 0) == -1)
 121                 fatal("Couldn't wait for ssh-rand-helper completion: %s",
 122                     strerror(errno));
 123         signal(SIGCHLD, old_sigchld);
 124
 125         /* We don't mind if the child exits upon a SIGPIPE */
 126         if (!WIFEXITED(ret) &&
 127             (!WIFSIGNALED(ret) || WTERMSIG(ret) != SIGPIPE))
 128                 fatal("ssh-rand-helper terminated abnormally");
 129         if (WEXITSTATUS(ret) != 0)
 130                 fatal("ssh-rand-helper exit with exit status %d", ret);
 131
 132         RAND_add(buf, sizeof(buf), sizeof(buf));
 133         memset(buf, '\0', sizeof(buf));
 134
 135 #endif /* OPENSSL_PRNG_ONLY */
 136         if (RAND_status() != 1)
 137                 fatal("PRNG is not seeded");
 138 }
 139
 140 void
 141 init_rng(void)
 142 {
 143         /*
 144          * OpenSSL version numbers: MNNFFPPS: major minor fix patch status
 145          * We match major, minor, fix and status (not patch)
 146          */
 147         if ((SSLeay() ^ OPENSSL_VERSION_NUMBER) & ~0xff0L)
 148                 fatal("OpenSSL version mismatch. Built against %lx, you "
 149                     "have %lx", OPENSSL_VERSION_NUMBER, SSLeay());
 150
 151 #ifndef OPENSSL_PRNG_ONLY
 152         original_uid = getuid();
 153         original_euid = geteuid();
 154 #endif
 155 }
 156
 157 #ifndef OPENSSL_PRNG_ONLY
 158 void
 159 rexec_send_rng_seed(Buffer *m)
 160 {
 161         u_char buf[RANDOM_SEED_SIZE];
 162
 163         if (RAND_bytes(buf, sizeof(buf)) <= 0) {
 164                 error("Couldn't obtain random bytes (error %ld)",
 165                     ERR_get_error());
 166                 buffer_put_string(m, "", 0);
 167         } else
 168                 buffer_put_string(m, buf, sizeof(buf));
 169 }
 170
 171 void
 172 rexec_recv_rng_seed(Buffer *m)
 173 {
 174         u_char *buf;
 175         u_int len;
 176
 177         buf = buffer_get_string_ret(m, &len);
 178         if (buf != NULL) {
 179                 debug3("rexec_recv_rng_seed: seeding rng with %u bytes", len);
 180                 RAND_add(buf, len, len);
 181         }
 182 }
 183 #endif