lib/getrandom.c

   1 /* Obtain a series of random bytes.
   2
   3    Copyright 2020-2024 Free Software Foundation, Inc.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Paul Eggert.  */
  19
  20 #include <config.h>
  21
  22 #include <sys/random.h>
  23
  24 #include <errno.h>
  25 #include <fcntl.h>
  26 #include <unistd.h>
  27
  28 #if defined _WIN32 && ! defined __CYGWIN__
  29 # define WIN32_LEAN_AND_MEAN
  30 # include <windows.h>
  31 # if HAVE_BCRYPT_H
  32 #  include <bcrypt.h>
  33 # else
  34 #  define NTSTATUS LONG
  35 typedef void * BCRYPT_ALG_HANDLE;
  36 #  define BCRYPT_USE_SYSTEM_PREFERRED_RNG 0x00000002
  37 #  if HAVE_LIB_BCRYPT
  38 extern NTSTATUS WINAPI BCryptGenRandom (BCRYPT_ALG_HANDLE, UCHAR *, ULONG, ULONG);
  39 #  endif
  40 # endif
  41 # if !HAVE_LIB_BCRYPT
  42 #  include <wincrypt.h>
  43 #  ifndef CRYPT_VERIFY_CONTEXT
  44 #   define CRYPT_VERIFY_CONTEXT 0xF0000000
  45 #  endif
  46 # endif
  47 #endif
  48
  49 #include "minmax.h"
  50
  51 #if defined _WIN32 && ! defined __CYGWIN__
  52
  53 /* Don't assume that UNICODE is not defined.  */
  54 # undef LoadLibrary
  55 # define LoadLibrary LoadLibraryA
  56 # undef CryptAcquireContext
  57 # define CryptAcquireContext CryptAcquireContextA
  58
  59 # if !HAVE_LIB_BCRYPT
  60
  61 /* Avoid warnings from gcc -Wcast-function-type.  */
  62 #  define GetProcAddress \
  63     (void *) GetProcAddress
  64
  65 /* BCryptGenRandom with the BCRYPT_USE_SYSTEM_PREFERRED_RNG flag works only
  66    starting with Windows 7.  */
  67 typedef NTSTATUS (WINAPI * BCryptGenRandomFuncType) (BCRYPT_ALG_HANDLE, UCHAR *, ULONG, ULONG);
  68 static BCryptGenRandomFuncType BCryptGenRandomFunc = NULL;
  69 static BOOL initialized = FALSE;
  70
  71 static void
  72 initialize (void)
  73 {
  74   HMODULE bcrypt = LoadLibrary ("bcrypt.dll");
  75   if (bcrypt != NULL)
  76     {
  77       BCryptGenRandomFunc =
  78         (BCryptGenRandomFuncType) GetProcAddress (bcrypt, "BCryptGenRandom");
  79     }
  80   initialized = TRUE;
  81 }
  82
  83 # else
  84
  85 #  define BCryptGenRandomFunc BCryptGenRandom
  86
  87 # endif
  88
  89 #else
  90 /* These devices exist on all platforms except native Windows.  */
  91
  92 /* Name of a device through which the kernel returns high quality random
  93    numbers, from an entropy pool.  When the pool is empty, the call blocks
  94    until entropy sources have added enough bits of entropy.  */
  95 # ifndef NAME_OF_RANDOM_DEVICE
  96 #  define NAME_OF_RANDOM_DEVICE "/dev/random"
  97 # endif
  98
  99 /* Name of a device through which the kernel returns random or pseudo-random
 100    numbers.  It uses an entropy pool, but, in order to avoid blocking, adds
 101    bits generated by a pseudo-random number generator, as needed.  */
 102 # ifndef NAME_OF_NONCE_DEVICE
 103 #  define NAME_OF_NONCE_DEVICE "/dev/urandom"
 104 # endif
 105
 106 #endif
 107
 108 /* Set BUFFER (of size LENGTH) to random bytes under the control of FLAGS.
 109    Return the number of bytes written (> 0).
 110    Upon error, return -1 and set errno.  */
 111 ssize_t
 112 getrandom (void *buffer, size_t length, unsigned int flags)
 113 #undef getrandom
 114 {
 115 #if defined _WIN32 && ! defined __CYGWIN__
 116   /* BCryptGenRandom, defined in <bcrypt.h>
 117      <https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom>
 118      with the BCRYPT_USE_SYSTEM_PREFERRED_RNG flag
 119      works in Windows 7 and newer.  */
 120   static int bcrypt_not_working /* = 0 */;
 121   if (!bcrypt_not_working)
 122     {
 123 # if !HAVE_LIB_BCRYPT
 124       if (!initialized)
 125         initialize ();
 126 # endif
 127       if (BCryptGenRandomFunc != NULL
 128           && BCryptGenRandomFunc (NULL, buffer, length,
 129                                   BCRYPT_USE_SYSTEM_PREFERRED_RNG)
 130              == 0 /*STATUS_SUCCESS*/)
 131         return length;
 132       bcrypt_not_working = 1;
 133     }
 134 # if !HAVE_LIB_BCRYPT
 135   /* CryptGenRandom, defined in <wincrypt.h>
 136      <https://docs.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-cryptgenrandom>
 137      works in older releases as well, but is now deprecated.
 138      CryptAcquireContext, defined in <wincrypt.h>
 139      <https://docs.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-cryptacquirecontexta>  */
 140   {
 141     static int crypt_initialized /* = 0 */;
 142     static HCRYPTPROV provider;
 143     if (!crypt_initialized)
 144       {
 145         if (CryptAcquireContext (&provider, NULL, NULL, PROV_RSA_FULL,
 146                                  CRYPT_VERIFY_CONTEXT))
 147           crypt_initialized = 1;
 148         else
 149           crypt_initialized = -1;
 150       }
 151     if (crypt_initialized >= 0)
 152       {
 153         if (!CryptGenRandom (provider, length, buffer))
 154           {
 155             errno = EIO;
 156             return -1;
 157           }
 158         return length;
 159       }
 160   }
 161 # endif
 162   errno = ENOSYS;
 163   return -1;
 164 #elif HAVE_GETRANDOM
 165   return getrandom (buffer, length, flags);
 166 #else
 167   static int randfd[2] = { -1, -1 };
 168   bool devrandom = (flags & GRND_RANDOM) != 0;
 169   int fd = randfd[devrandom];
 170
 171   if (fd < 0)
 172     {
 173       static char const randdevice[][MAX (sizeof NAME_OF_NONCE_DEVICE,
 174                                           sizeof NAME_OF_RANDOM_DEVICE)]
 175         = { NAME_OF_NONCE_DEVICE, NAME_OF_RANDOM_DEVICE };
 176       int oflags = (O_RDONLY + O_CLOEXEC
 177                     + (flags & GRND_NONBLOCK ? O_NONBLOCK : 0));
 178       fd = open (randdevice[devrandom], oflags);
 179       if (fd < 0)
 180         {
 181           if (errno == ENOENT || errno == ENOTDIR)
 182             errno = ENOSYS;
 183           return -1;
 184         }
 185       randfd[devrandom] = fd;
 186     }
 187
 188   return read (fd, buffer, length);
 189 #endif
 190 }