sysdeps/mach/hurd/getentropy.c

   1 /* Implementation of getentropy based on getrandom.
   2    Copyright (C) 2016-2022 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library 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 GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <sys/random.h>
  20 #include <assert.h>
  21 #include <errno.h>
  22 #include <unistd.h>
  23
  24 /* Write LENGTH bytes of randomness starting at BUFFER.  Return 0 on
  25    success and -1 on failure.  */
  26 int
  27 getentropy (void *buffer, size_t length)
  28 {
  29   /* The interface is documented to return EIO for buffer lengths
  30      longer than 256 bytes.  */
  31   if (length > 256)
  32     {
  33       __set_errno (EIO);
  34       return -1;
  35     }
  36
  37   /* Try to fill the buffer completely.  Even with the 256 byte limit
  38      above, we might still receive an EINTR error (when blocking
  39      during boot).  */
  40   void *end = buffer + length;
  41   while (buffer < end)
  42     {
  43       /* NB: No cancellation point.  */
  44       ssize_t bytes = __getrandom (buffer, end - buffer, 0);
  45       if (bytes < 0)
  46         {
  47           if (errno == EINTR)
  48             /* Try again if interrupted by a signal.  */
  49             continue;
  50           else
  51             return -1;
  52         }
  53       if (bytes == 0)
  54         {
  55           /* No more bytes available.  This should not happen under
  56              normal circumstances.  */
  57           __set_errno (EIO);
  58           return -1;
  59         }
  60       /* Try again in case of a short read.  */
  61       buffer += bytes;
  62     }
  63   return 0;
  64 }