debug/vsnprintf_chk.c

   1 /* Copyright (C) 1991-2017 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    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <stdarg.h>
  19 #include <stdio.h>
  20 #include "../libio/libioP.h"
  21 #include "../libio/strfile.h"
  22
  23 extern const struct _IO_jump_t _IO_strn_jumps libio_vtable attribute_hidden;
  24
  25 /* Write formatted output into S, according to the format
  26    string FORMAT, writing no more than MAXLEN characters.  */
  27 /* VARARGS5 */
  28 int
  29 ___vsnprintf_chk (char *s, size_t maxlen, int flags, size_t slen,
  30                   const char *format, va_list args)
  31 {
  32   /* XXX Maybe for less strict version do not fail immediately.
  33      Though, maxlen is supposed to be the size of buffer pointed
  34      to by s, so a conforming program can't pass such maxlen
  35      to *snprintf.  */
  36   if (__glibc_unlikely (slen < maxlen))
  37     __chk_fail ();
  38
  39   _IO_strnfile sf;
  40   int ret;
  41 #ifdef _IO_MTSAFE_IO
  42   sf.f._sbf._f._lock = NULL;
  43 #endif
  44
  45   /* We need to handle the special case where MAXLEN is 0.  Use the
  46      overflow buffer right from the start.  */
  47   if (maxlen == 0)
  48     {
  49       s = sf.overflow_buf;
  50       maxlen = sizeof (sf.overflow_buf);
  51     }
  52
  53   _IO_no_init (&sf.f._sbf._f, _IO_USER_LOCK, -1, NULL, NULL);
  54   _IO_JUMPS (&sf.f._sbf) = &_IO_strn_jumps;
  55   s[0] = '\0';
  56
  57   /* For flags > 0 (i.e. __USE_FORTIFY_LEVEL > 1) request that %n
  58      can only come from read-only format strings.  */
  59   if (flags > 0)
  60     sf.f._sbf._f._flags2 |= _IO_FLAGS2_FORTIFY;
  61
  62   _IO_str_init_static_internal (&sf.f, s, maxlen - 1, s);
  63   ret = _IO_vfprintf (&sf.f._sbf._f, format, args);
  64
  65   if (sf.f._sbf._f._IO_buf_base != sf.overflow_buf)
  66     *sf.f._sbf._f._IO_write_ptr = '\0';
  67   return ret;
  68 }
  69 ldbl_hidden_def (___vsnprintf_chk, __vsnprintf_chk)
  70 ldbl_strong_alias (___vsnprintf_chk, __vsnprintf_chk)