1  /* Pseudo Random Number Generator
       2     Copyright (C) 2022-2023 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 <errno.h>
      20  #include <not-cancel.h>
      21  #include <stdio.h>
      22  #include <stdlib.h>
      23  #include <sys/mman.h>
      24  #include <sys/param.h>
      25  #include <sys/random.h>
      26  
      27  static void
      28  arc4random_getrandom_failure (void)
      29  {
      30    __libc_fatal ("Fatal glibc error: cannot get entropy for arc4random\n");
      31  }
      32  
      33  void
      34  __arc4random_buf (void *p, size_t n)
      35  {
      36    static int seen_initialized;
      37    ssize_t l;
      38    int fd;
      39  
      40    if (n == 0)
      41      return;
      42  
      43    for (;;)
      44      {
      45        l = TEMP_FAILURE_RETRY (__getrandom_nocancel (p, n, 0));
      46        if (l > 0)
      47  	{
      48  	  if ((size_t) l == n)
      49  	    return; /* Done reading, success.  */
      50  	  p = (uint8_t *) p + l;
      51  	  n -= l;
      52  	  continue; /* Interrupted by a signal; keep going.  */
      53  	}
      54        else if (l == -ENOSYS)
      55  	break; /* No syscall, so fallback to /dev/urandom.  */
      56        arc4random_getrandom_failure ();
      57      }
      58  
      59    if (atomic_load_relaxed (&seen_initialized) == 0)
      60      {
      61        /* Poll /dev/random as an approximation of RNG initialization.  */
      62        struct pollfd pfd = { .events = POLLIN };
      63        pfd.fd = TEMP_FAILURE_RETRY (
      64  	  __open64_nocancel ("/dev/random", O_RDONLY | O_CLOEXEC | O_NOCTTY));
      65        if (pfd.fd < 0)
      66  	arc4random_getrandom_failure ();
      67        if (TEMP_FAILURE_RETRY (__poll_infinity_nocancel (&pfd, 1)) < 0)
      68  	arc4random_getrandom_failure ();
      69        if (__close_nocancel (pfd.fd) < 0)
      70  	arc4random_getrandom_failure ();
      71        atomic_store_relaxed (&seen_initialized, 1);
      72      }
      73  
      74    fd = TEMP_FAILURE_RETRY (
      75        __open64_nocancel ("/dev/urandom", O_RDONLY | O_CLOEXEC | O_NOCTTY));
      76    if (fd < 0)
      77      arc4random_getrandom_failure ();
      78    for (;;)
      79      {
      80        l = TEMP_FAILURE_RETRY (__read_nocancel (fd, p, n));
      81        if (l <= 0)
      82  	arc4random_getrandom_failure ();
      83        if ((size_t) l == n)
      84  	break; /* Done reading, success.  */
      85        p = (uint8_t *) p + l;
      86        n -= l;
      87      }
      88    if (__close_nocancel (fd) < 0)
      89      arc4random_getrandom_failure ();
      90  }
      91  libc_hidden_def (__arc4random_buf)
      92  weak_alias (__arc4random_buf, arc4random_buf)
      93  
      94  uint32_t
      95  __arc4random (void)
      96  {
      97    uint32_t r;
      98    __arc4random_buf (&r, sizeof (r));
      99    return r;
     100  }
     101  libc_hidden_def (__arc4random)
     102  weak_alias (__arc4random, arc4random)