crypto/openssh-4/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 <unistd.h>
  39 #include <signal.h>
  40
  41 #include <openssl/rand.h>
  42 #include <openssl/crypto.h>
  43 #include <openssl/err.h>
  44
  45 #include "ssh.h"
  46 #include "misc.h"
  47 #include "xmalloc.h"
  48 #include "atomicio.h"
  49 #include "pathnames.h"
  50 #include "log.h"
  51 #include "buffer.h"
  52
  53 /*
  54  * Portable OpenSSH PRNG seeding:
  55  * If OpenSSL has not "internally seeded" itself (e.g. pulled data from
  56  * /dev/random), then we execute a "ssh-rand-helper" program which
  57  * collects entropy and writes it to stdout. The child program must
  58  * write at least RANDOM_SEED_SIZE bytes. The child is run with stderr
  59  * attached, so error/debugging output should be visible.
  60  *
  61  * XXX: we should tell the child how many bytes we need.
  62  */
  63
  64 #ifndef OPENSSL_PRNG_ONLY
  65 #define RANDOM_SEED_SIZE 48
  66 static uid_t original_uid, original_euid;
  67 #endif
  68
  69 void
  70 seed_rng(void)
  71 {
  72 #ifndef OPENSSL_PRNG_ONLY
  73         int devnull;
  74         int p[2];
  75         pid_t pid;
  76         int ret;
  77         unsigned char buf[RANDOM_SEED_SIZE];
  78         mysig_t old_sigchld;
  79
  80         if (RAND_status() == 1) {
  81                 debug3("RNG is ready, skipping seeding");
  82                 return;
  83         }
  84
  85         debug3("Seeding PRNG from %s", SSH_RAND_HELPER);
  86
  87         if ((devnull = open("/dev/null", O_RDWR)) == -1)
  88                 fatal("Couldn't open /dev/null: %s", strerror(errno));
  89         if (pipe(p) == -1)
  90                 fatal("pipe: %s", strerror(errno));
  91
  92         old_sigchld = signal(SIGCHLD, SIG_DFL);
  93         if ((pid = fork()) == -1)
  94                 fatal("Couldn't fork: %s", strerror(errno));
  95         if (pid == 0) {
  96                 dup2(devnull, STDIN_FILENO);
  97                 dup2(p[1], STDOUT_FILENO);
  98                 /* Keep stderr open for errors */
  99                 close(p[0]);
 100                 close(p[1]);
 101                 close(devnull);
 102
 103                 if (original_uid != original_euid &&
 104                     ( seteuid(getuid()) == -1 ||
 105                       setuid(original_uid) == -1) ) {
 106                         fprintf(stderr, "(rand child) setuid(%li): %s\n",
 107                             (long int)original_uid, strerror(errno));
 108                         _exit(1);
 109                 }
 110
 111                 execl(SSH_RAND_HELPER, "ssh-rand-helper", NULL);
 112                 fprintf(stderr, "(rand child) Couldn't exec '%s': %s\n",
 113                     SSH_RAND_HELPER, strerror(errno));
 114                 _exit(1);
 115         }
 116
 117         close(devnull);
 118         close(p[1]);
 119
 120         memset(buf, '\0', sizeof(buf));
 121         ret = atomicio(read, p[0], buf, sizeof(buf));
 122         if (ret == -1)
 123                 fatal("Couldn't read from ssh-rand-helper: %s",
 124                     strerror(errno));
 125         if (ret != sizeof(buf))
 126                 fatal("ssh-rand-helper child produced insufficient data");
 127
 128         close(p[0]);
 129
 130         if (waitpid(pid, &ret, 0) == -1)
 131                 fatal("Couldn't wait for ssh-rand-helper completion: %s",
 132                     strerror(errno));
 133         signal(SIGCHLD, old_sigchld);
 134
 135         /* We don't mind if the child exits upon a SIGPIPE */
 136         if (!WIFEXITED(ret) &&
 137             (!WIFSIGNALED(ret) || WTERMSIG(ret) != SIGPIPE))
 138                 fatal("ssh-rand-helper terminated abnormally");
 139         if (WEXITSTATUS(ret) != 0)
 140                 fatal("ssh-rand-helper exit with exit status %d", ret);
 141
 142         RAND_add(buf, sizeof(buf), sizeof(buf));
 143         memset(buf, '\0', sizeof(buf));
 144
 145 #endif /* OPENSSL_PRNG_ONLY */
 146         if (RAND_status() != 1)
 147                 fatal("PRNG is not seeded");
 148 }
 149
 150 void
 151 init_rng(void)
 152 {
 153         /*
 154          * OpenSSL version numbers: MNNFFPPS: major minor fix patch status
 155          * We match major, minor, fix and status (not patch)
 156          */
 157         if ((SSLeay() ^ OPENSSL_VERSION_NUMBER) & ~0xff0L)
 158                 fatal("OpenSSL version mismatch. Built against %lx, you "
 159                     "have %lx", OPENSSL_VERSION_NUMBER, SSLeay());
 160
 161 #ifndef OPENSSL_PRNG_ONLY
 162         original_uid = getuid();
 163         original_euid = geteuid();
 164 #endif
 165 }
 166
 167 #ifndef OPENSSL_PRNG_ONLY
 168 void
 169 rexec_send_rng_seed(Buffer *m)
 170 {
 171         u_char buf[RANDOM_SEED_SIZE];
 172
 173         if (RAND_bytes(buf, sizeof(buf)) <= 0) {
 174                 error("Couldn't obtain random bytes (error %ld)",
 175                     ERR_get_error());
 176                 buffer_put_string(m, "", 0);
 177         } else
 178                 buffer_put_string(m, buf, sizeof(buf));
 179 }
 180
 181 void
 182 rexec_recv_rng_seed(Buffer *m)
 183 {
 184         u_char *buf;
 185         u_int len;
 186
 187         buf = buffer_get_string_ret(m, &len);
 188         if (buf != NULL) {
 189                 debug3("rexec_recv_rng_seed: seeding rng with %u bytes", len);
 190                 RAND_add(buf, len, len);
 191         }
 192 }
 193 #endif