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 2 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, write to the Free Software
  19    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20 */
  21
  22 #include "includes.h"
  23
  24 #ifdef DEVELOPER
  25 const char *global_clobber_region_function;
  26 unsigned int global_clobber_region_line;
  27 #endif
  28
  29 /**
  30  * In developer builds, clobber a region of memory.
  31  *
  32  * If we think a string buffer is longer than it really is, this ought
  33  * to make the failure obvious, by segfaulting (if in the heap) or by
  34  * killing the return address (on the stack), or by trapping under a
  35  * memory debugger.
  36  *
  37  * This is meant to catch possible string overflows, even if the
  38  * actual string copied is not big enough to cause an overflow.
  39  *
  40  * In addition, under Valgrind the buffer is marked as uninitialized.
  41  **/
  42 void clobber_region(const char *fn, unsigned int line, char *dest, size_t len)
  43 {
  44 #ifdef DEVELOPER
  45         global_clobber_region_function = fn;
  46         global_clobber_region_line = line;
  47
  48         /* F1 is odd and 0xf1f1f1f1 shouldn't be a valid pointer */
  49         memset(dest, 0xF1, len);
  50 #ifdef VALGRIND
  51         /* Even though we just wrote to this, from the application's
  52          * point of view it is not initialized.
  53          *
  54          * (This is not redundant with the clobbering above.  The
  55          * marking might not actually take effect if we're not running
  56          * under valgrind.) */
  57         VALGRIND_MAKE_WRITABLE(dest, len);
  58 #endif /* VALGRIND */
  59 #endif /* DEVELOPER */
  60 }