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 <openssl/rand.h>
  28 #include <openssl/crypto.h>
  29
  30 #include "ssh.h"
  31 #include "misc.h"
  32 #include "xmalloc.h"
  33 #include "atomicio.h"
  34 #include "pathnames.h"
  35 #include "log.h"
  36
  37 /*
  38  * Portable OpenSSH PRNG seeding:
  39  * If OpenSSL has not "internally seeded" itself (e.g. pulled data from
  40  * /dev/random), then we execute a "ssh-rand-helper" program which
  41  * collects entropy and writes it to stdout. The child program must
  42  * write at least RANDOM_SEED_SIZE bytes. The child is run with stderr
  43  * attached, so error/debugging output should be visible.
  44  *
  45  * XXX: we should tell the child how many bytes we need.
  46  */
  47
  48 RCSID("$Id: entropy.c,v 1.49 2005/07/17 07:26:44 djm Exp $");
  49
  50 #ifndef OPENSSL_PRNG_ONLY
  51 #define RANDOM_SEED_SIZE 48
  52 static uid_t original_uid, original_euid;
  53 #endif
  54
  55 void
  56 seed_rng(void)
  57 {
  58 #ifndef OPENSSL_PRNG_ONLY
  59         int devnull;
  60         int p[2];
  61         pid_t pid;
  62         int ret;
  63         unsigned char buf[RANDOM_SEED_SIZE];
  64         mysig_t old_sigchld;
  65
  66         if (RAND_status() == 1) {
  67                 debug3("RNG is ready, skipping seeding");
  68                 return;
  69         }
  70
  71         debug3("Seeding PRNG from %s", SSH_RAND_HELPER);
  72
  73         if ((devnull = open("/dev/null", O_RDWR)) == -1)
  74                 fatal("Couldn't open /dev/null: %s", strerror(errno));
  75         if (pipe(p) == -1)
  76                 fatal("pipe: %s", strerror(errno));
  77
  78         old_sigchld = signal(SIGCHLD, SIG_DFL);
  79         if ((pid = fork()) == -1)
  80                 fatal("Couldn't fork: %s", strerror(errno));
  81         if (pid == 0) {
  82                 dup2(devnull, STDIN_FILENO);
  83                 dup2(p[1], STDOUT_FILENO);
  84                 /* Keep stderr open for errors */
  85                 close(p[0]);
  86                 close(p[1]);
  87                 close(devnull);
  88
  89                 if (original_uid != original_euid &&
  90                     ( seteuid(getuid()) == -1 ||
  91                       setuid(original_uid) == -1) ) {
  92                         fprintf(stderr, "(rand child) setuid(%li): %s\n",
  93                             (long int)original_uid, strerror(errno));
  94                         _exit(1);
  95                 }
  96
  97                 execl(SSH_RAND_HELPER, "ssh-rand-helper", NULL);
  98                 fprintf(stderr, "(rand child) Couldn't exec '%s': %s\n",
  99                     SSH_RAND_HELPER, strerror(errno));
 100                 _exit(1);
 101         }
 102
 103         close(devnull);
 104         close(p[1]);
 105
 106         memset(buf, '\0', sizeof(buf));
 107         ret = atomicio(read, p[0], buf, sizeof(buf));
 108         if (ret == -1)
 109                 fatal("Couldn't read from ssh-rand-helper: %s",
 110                     strerror(errno));
 111         if (ret != sizeof(buf))
 112                 fatal("ssh-rand-helper child produced insufficient data");
 113
 114         close(p[0]);
 115
 116         if (waitpid(pid, &ret, 0) == -1)
 117                 fatal("Couldn't wait for ssh-rand-helper completion: %s",
 118                     strerror(errno));
 119         signal(SIGCHLD, old_sigchld);
 120
 121         /* We don't mind if the child exits upon a SIGPIPE */
 122         if (!WIFEXITED(ret) &&
 123             (!WIFSIGNALED(ret) || WTERMSIG(ret) != SIGPIPE))
 124                 fatal("ssh-rand-helper terminated abnormally");
 125         if (WEXITSTATUS(ret) != 0)
 126                 fatal("ssh-rand-helper exit with exit status %d", ret);
 127
 128         RAND_add(buf, sizeof(buf), sizeof(buf));
 129         memset(buf, '\0', sizeof(buf));
 130
 131 #endif /* OPENSSL_PRNG_ONLY */
 132         if (RAND_status() != 1)
 133                 fatal("PRNG is not seeded");
 134 }
 135
 136 void
 137 init_rng(void)
 138 {
 139         /*
 140          * OpenSSL version numbers: MNNFFPPS: major minor fix patch status
 141          * We match major, minor, fix and status (not patch)
 142          */
 143         if ((SSLeay() ^ OPENSSL_VERSION_NUMBER) & ~0xff0L)
 144                 fatal("OpenSSL version mismatch. Built against %lx, you "
 145                     "have %lx", OPENSSL_VERSION_NUMBER, SSLeay());
 146
 147 #ifndef OPENSSL_PRNG_ONLY
 148         if ((original_uid = getuid()) == -1)
 149                 fatal("getuid: %s", strerror(errno));
 150         if ((original_euid = geteuid()) == -1)
 151                 fatal("geteuid: %s", strerror(errno));
 152 #endif
 153 }
 154