gshadow/fgetsgent.c

   1 /* Copyright (C) 2009-2021 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 <libc-lock.h>
  20 #include <gshadow.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23
  24
  25 /* A reasonable size for a buffer to start with.  */
  26 #define BUFLEN_SPWD 1024
  27
  28 /* We need to protect the dynamic buffer handling.  */
  29 __libc_lock_define_initialized (static, lock);
  30
  31 libc_freeres_ptr (static char *buffer);
  32
  33 /* Read one shadow entry from the given stream.  */
  34 struct sgrp *
  35 fgetsgent (FILE *stream)
  36 {
  37   static size_t buffer_size;
  38   static struct sgrp resbuf;
  39   fpos_t pos;
  40   struct sgrp *result;
  41   int save;
  42
  43   if (fgetpos (stream, &pos) != 0)
  44     return NULL;
  45
  46   /* Get lock.  */
  47   __libc_lock_lock (lock);
  48
  49   /* Allocate buffer if not yet available.  */
  50   if (buffer == NULL)
  51     {
  52       buffer_size = BUFLEN_SPWD;
  53       buffer = malloc (buffer_size);
  54     }
  55
  56   while (buffer != NULL
  57          && (__fgetsgent_r (stream, &resbuf, buffer, buffer_size, &result)
  58              == ERANGE))
  59     {
  60       char *new_buf;
  61       buffer_size += BUFLEN_SPWD;
  62       new_buf = realloc (buffer, buffer_size);
  63       if (new_buf == NULL)
  64         {
  65           /* We are out of memory.  Free the current buffer so that the
  66              process gets a chance for a normal termination.  */
  67           save = errno;
  68           free (buffer);
  69           __set_errno (save);
  70         }
  71       buffer = new_buf;
  72
  73       /* Reset the stream.  */
  74       if (fsetpos (stream, &pos) != 0)
  75         buffer = NULL;
  76     }
  77
  78   if (buffer == NULL)
  79     result = NULL;
  80
  81   /* Release lock.  Preserve error value.  */
  82   save = errno;
  83   __libc_lock_unlock (lock);
  84   __set_errno (save);
  85
  86   return result;
  87 }