sysdeps/mach/hurd/getentropy.c

   1 /* Implementation of getentropy based on getrandom.
   2    Copyright (C) 2016-2024 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 #include <hurd.h>
  24
  25 /* Write LENGTH bytes of randomness starting at BUFFER.  Return 0 on
  26    success and -1 on failure.  */
  27 int
  28 getentropy (void *buffer, size_t length)
  29 {
  30   /* The interface is documented to return EIO for buffer lengths
  31      longer than 256 bytes.  */
  32   if (length > 256)
  33     return __hurd_fail (EIO);
  34
  35   /* Try to fill the buffer completely.  Even with the 256 byte limit
  36      above, we might still receive an EINTR error (when blocking
  37      during boot).  */
  38   void *end = buffer + length;
  39   while (buffer < end)
  40     {
  41       /* NB: No cancellation point.  */
  42       ssize_t bytes = __getrandom (buffer, end - buffer, 0);
  43       if (bytes < 0)
  44         {
  45           if (errno == EINTR)
  46             /* Try again if interrupted by a signal.  */
  47             continue;
  48           else
  49             return -1;
  50         }
  51       if (bytes == 0)
  52         /* No more bytes available.  This should not happen under
  53            normal circumstances.  */
  54         return __hurd_fail (EIO);
  55       /* Try again in case of a short read.  */
  56       buffer += bytes;
  57     }
  58   return 0;
  59 }