source4/heimdal/lib/krb5/crypto-rand.c

   1 /*
   2  * Copyright (c) 1997 - 2008 Kungliga Tekniska Högskolan
   3  * (Royal Institute of Technology, Stockholm, Sweden).
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  *
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  *
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  *
  17  * 3. Neither the name of the Institute nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  */
  33
  34 #include "krb5_locl.h"
  35
  36 #define ENTROPY_NEEDED 128
  37
  38 static HEIMDAL_MUTEX crypto_mutex = HEIMDAL_MUTEX_INITIALIZER;
  39
  40 static int
  41 seed_something(void)
  42 {
  43     char buf[1024], seedfile[256];
  44
  45     /* If there is a seed file, load it. But such a file cannot be trusted,
  46        so use 0 for the entropy estimate */
  47     if (RAND_file_name(seedfile, sizeof(seedfile))) {
  48         int fd;
  49         fd = open(seedfile, O_RDONLY | O_BINARY | O_CLOEXEC);
  50         if (fd >= 0) {
  51             ssize_t ret;
  52             rk_cloexec(fd);
  53             ret = read(fd, buf, sizeof(buf));
  54             if (ret > 0)
  55                 RAND_add(buf, ret, 0.0);
  56             close(fd);
  57         } else
  58             seedfile[0] = '\0';
  59     } else
  60         seedfile[0] = '\0';
  61
  62     /* Calling RAND_status() will try to use /dev/urandom if it exists so
  63        we do not have to deal with it. */
  64     if (RAND_status() != 1) {
  65 #ifndef _WIN32
  66         krb5_context context;
  67         const char *p;
  68
  69         /* Try using egd */
  70         if (!krb5_init_context(&context)) {
  71             p = krb5_config_get_string(context, NULL, "libdefaults",
  72                                        "egd_socket", NULL);
  73             if (p != NULL)
  74                 RAND_egd_bytes(p, ENTROPY_NEEDED);
  75             krb5_free_context(context);
  76         }
  77 #else
  78         /* TODO: Once a Windows CryptoAPI RAND method is defined, we
  79            can use that and failover to another method. */
  80 #endif
  81     }
  82
  83     if (RAND_status() == 1)     {
  84         /* Update the seed file */
  85         if (seedfile[0])
  86             RAND_write_file(seedfile);
  87
  88         return 0;
  89     } else
  90         return -1;
  91 }
  92
  93 KRB5_LIB_FUNCTION void KRB5_LIB_CALL
  94 krb5_generate_random_block(void *buf, size_t len)
  95 {
  96     static int rng_initialized = 0;
  97
  98     HEIMDAL_MUTEX_lock(&crypto_mutex);
  99     if (!rng_initialized) {
 100         if (seed_something())
 101             krb5_abortx(NULL, "Fatal: could not seed the "
 102                         "random number generator");
 103
 104         rng_initialized = 1;
 105     }
 106     HEIMDAL_MUTEX_unlock(&crypto_mutex);
 107     if (RAND_bytes(buf, len) <= 0)
 108         krb5_abortx(NULL, "Failed to generate random block");
 109 }