malloc/tst-tcfree3.c

   1 /* Test that malloc tcache catches double free.
   2    Copyright (C) 2018-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <malloc.h>
  20 #include <string.h>
  21
  22 /* Prevent GCC from optimizing away any malloc/free pairs.  */
  23 #pragma GCC optimize ("O0")
  24
  25 static int
  26 do_test (void)
  27 {
  28   /* Do two allocation of any size that fit in tcache, and one that
  29      doesn't.  */
  30   int ** volatile a = malloc (32);
  31   int ** volatile b = malloc (32);
  32   /* This is just under the mmap threshold.  */
  33   int ** volatile c = malloc (127 * 1024);
  34
  35   /* The invalid "tcache bucket" we might dereference will likely end
  36      up somewhere within this memory block, so make all the accidental
  37      "next" pointers cause segfaults.  BZ #23907.  */
  38   memset (c, 0xff, 127 * 1024);
  39
  40   free (a); // puts in tcache
  41
  42   /* A is now free and contains the key we use to detect in-tcache.
  43      Copy the key to the other chunks.  */
  44   memcpy (b, a, 32);
  45   memcpy (c, a, 32);
  46
  47   /* This free tests the "are we in the tcache already" loop with a
  48      VALID bin but "coincidental" matching key.  */
  49   free (b); // should NOT abort
  50   /* This free tests the "is it a valid tcache bin" test.  */
  51   free (c); // should NOT abort
  52
  53   return 0;
  54 }
  55
  56 #include <support/test-driver.c>