nss/fgetgrent.c

   1 /* Copyright (C) 1991-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library 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 GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <grp.h>
  20 #include <libc-lock.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <set-freeres.h>
  24
  25
  26 /* We need to protect the dynamic buffer handling.  */
  27 __libc_lock_define_initialized (static, lock);
  28
  29 static char *buffer;
  30
  31 /* Read one entry from the given stream.  */
  32 struct group *
  33 fgetgrent (FILE *stream)
  34 {
  35   static size_t buffer_size;
  36   static struct group resbuf;
  37   fpos_t pos;
  38   struct group *result;
  39   int save;
  40
  41   if (__builtin_expect (fgetpos (stream, &pos), 0) != 0)
  42     return NULL;
  43
  44   /* Get lock.  */
  45   __libc_lock_lock (lock);
  46
  47   /* Allocate buffer if not yet available.  */
  48   if (buffer == NULL)
  49     {
  50       buffer_size = NSS_BUFLEN_GROUP;
  51       buffer = malloc (buffer_size);
  52     }
  53
  54   while (buffer != NULL
  55          && (__fgetgrent_r (stream, &resbuf, buffer, buffer_size, &result)
  56              == ERANGE))
  57     {
  58       char *new_buf;
  59       buffer_size += NSS_BUFLEN_GROUP;
  60       new_buf = realloc (buffer, buffer_size);
  61       if (__glibc_unlikely (new_buf == NULL))
  62         {
  63           /* We are out of memory.  Free the current buffer so that the
  64              process gets a chance for a normal termination.  */
  65           save = errno;
  66           free (buffer);
  67           __set_errno (save);
  68         }
  69       buffer = new_buf;
  70
  71       /* Reset the stream.  */
  72       if (fsetpos (stream, &pos) != 0)
  73         buffer = NULL;
  74     }
  75
  76   if (buffer == NULL)
  77     result = NULL;
  78
  79   /* Release lock.  Preserve error value.  */
  80   save = errno;
  81   __libc_lock_unlock (lock);
  82   __set_errno (save);
  83
  84   return result;
  85 }
  86
  87 weak_alias (buffer, __libc_fgetgrent_freemem_ptr)