1  /* Implementation of getentropy based on getrandom.
       2     Copyright (C) 2016-2023 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  }