lib/getentropy.c

   1 /* Fill a buffer with random bytes.
   2    Copyright 2020 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Paul Eggert.  */
  18
  19 #include <config.h>
  20
  21 #include <unistd.h>
  22
  23 #include <errno.h>
  24 #include <sys/random.h>
  25
  26 /* Overwrite BUFFER with random data.  BUFFER contains LENGTH bytes.
  27    LENGTH must be at most 256.  Return 0 on success, -1 (setting
  28    errno) on failure.  */
  29 int
  30 getentropy (void *buffer, size_t length)
  31 {
  32   char *buf = buffer;
  33
  34   if (length <= 256)
  35     for (;;)
  36       {
  37         ssize_t bytes;
  38         if (length == 0)
  39           return 0;
  40         while ((bytes = getrandom (buf, length, 0)) < 0)
  41           if (errno != EINTR)
  42             return -1;
  43         if (bytes == 0)
  44           break;
  45         buf += bytes;
  46         length -= bytes;
  47       }
  48
  49   errno = EIO;
  50   return -1;
  51 }