source/lib/clobber.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3    Samba utility functions
   4    Copyright (C) Martin Pool     2003
   5    Copyright (C) Andrew Bartlett 2003
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  19 */
  20
  21 #include "includes.h"
  22
  23 #ifdef DEVELOPER
  24 const char *global_clobber_region_function;
  25 unsigned int global_clobber_region_line;
  26 #endif
  27
  28 /**
  29  * In developer builds, clobber a region of memory.
  30  *
  31  * If we think a string buffer is longer than it really is, this ought
  32  * to make the failure obvious, by segfaulting (if in the heap) or by
  33  * killing the return address (on the stack), or by trapping under a
  34  * memory debugger.
  35  *
  36  * This is meant to catch possible string overflows, even if the
  37  * actual string copied is not big enough to cause an overflow.
  38  *
  39  * In addition, under Valgrind the buffer is marked as uninitialized.
  40  **/
  41 void clobber_region(const char *fn, unsigned int line, char *dest, size_t len)
  42 {
  43 #ifdef DEVELOPER
  44         global_clobber_region_function = fn;
  45         global_clobber_region_line = line;
  46
  47         /* F1 is odd and 0xf1f1f1f1 shouldn't be a valid pointer */
  48         memset(dest, 0xF1, len);
  49 #ifdef VALGRIND
  50         /* Even though we just wrote to this, from the application's
  51          * point of view it is not initialized.
  52          *
  53          * (This is not redundant with the clobbering above.  The
  54          * marking might not actually take effect if we're not running
  55          * under valgrind.) */
  56 #if defined(VALGRIND_MAKE_MEM_UNDEFINED)
  57         VALGRIND_MAKE_MEM_UNDEFINED(dest, len);
  58 #elif defined(VALGRIND_MAKE_WRITABLE)
  59         VALGRIND_MAKE_WRITABLE(dest, len);
  60 #endif
  61 #endif /* VALGRIND */
  62 #endif /* DEVELOPER */
  63 }