grp/fgetgrent.c

   1 /* Copyright (C) 1991-2022 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
  24
  25 /* We need to protect the dynamic buffer handling.  */
  26 __libc_lock_define_initialized (static, lock);
  27
  28 libc_freeres_ptr (static char *buffer);
  29
  30 /* Read one entry from the given stream.  */
  31 struct group *
  32 fgetgrent (FILE *stream)
  33 {
  34   static size_t buffer_size;
  35   static struct group resbuf;
  36   fpos_t pos;
  37   struct group *result;
  38   int save;
  39
  40   if (__builtin_expect (fgetpos (stream, &pos), 0) != 0)
  41     return NULL;
  42
  43   /* Get lock.  */
  44   __libc_lock_lock (lock);
  45
  46   /* Allocate buffer if not yet available.  */
  47   if (buffer == NULL)
  48     {
  49       buffer_size = NSS_BUFLEN_GROUP;
  50       buffer = malloc (buffer_size);
  51     }
  52
  53   while (buffer != NULL
  54          && (__fgetgrent_r (stream, &resbuf, buffer, buffer_size, &result)
  55              == ERANGE))
  56     {
  57       char *new_buf;
  58       buffer_size += NSS_BUFLEN_GROUP;
  59       new_buf = realloc (buffer, buffer_size);
  60       if (__glibc_unlikely (new_buf == NULL))
  61         {
  62           /* We are out of memory.  Free the current buffer so that the
  63              process gets a chance for a normal termination.  */
  64           save = errno;
  65           free (buffer);
  66           __set_errno (save);
  67         }
  68       buffer = new_buf;
  69
  70       /* Reset the stream.  */
  71       if (fsetpos (stream, &pos) != 0)
  72         buffer = NULL;
  73     }
  74
  75   if (buffer == NULL)
  76     result = NULL;
  77
  78   /* Release lock.  Preserve error value.  */
  79   save = errno;
  80   __libc_lock_unlock (lock);
  81   __set_errno (save);
  82
  83   return result;
  84 }