path: root/malloc/hooks.c

/* Malloc implementation for multiple threads without lock contention.
   Copyright (C) 2001-2020 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Wolfram Gloger <wg@malloc.de>, 2001.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation; either version 2.1 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If
   not, see <https://www.gnu.org/licenses/>.  */

/* What to do if the standard debugging hooks are in place and a
   corrupt pointer is detected: do nothing (0), print an error message
   (1), or call abort() (2). */

/* Hooks for debugging versions.  The initial hooks just call the
   initialization routine, then do the normal work. */

static void *
malloc_hook_ini (size_t sz, const void *caller)
{
  __malloc_hook = NULL;
  ptmalloc_init ();
  return __libc_malloc (sz);
}

static void *
realloc_hook_ini (void *ptr, size_t sz, const void *caller)
{
  __malloc_hook = NULL;
  __realloc_hook = NULL;
  ptmalloc_init ();
  return __libc_realloc (ptr, sz);
}

static void *
memalign_hook_ini (size_t alignment, size_t sz, const void *caller)
{
  __memalign_hook = NULL;
  ptmalloc_init ();
  return __libc_memalign (alignment, sz);
}

/* Whether we are using malloc checking.  */
static int using_malloc_checking;

/* Activate a standard set of debugging hooks. */
void
__malloc_check_init (void)
{
  using_malloc_checking = 1;
  __malloc_hook = malloc_check;
  __free_hook = free_check;
  __realloc_hook = realloc_check;
  __memalign_hook = memalign_check;
}

/* A simple, standard set of debugging hooks.  Overhead is `only' one
   byte per chunk; still this will catch most cases of double frees or
   overruns.  The goal here is to avoid obscure crashes due to invalid
   usage, unlike in the MALLOC_DEBUG code. */

static unsigned char
magicbyte (const void *p)
{
  unsigned char magic;

  magic = (((uintptr_t) p >> 3) ^ ((uintptr_t) p >> 11)) & 0xFF;
  /* Do not return 1.  See the comment in mem2mem_check().  */
  if (magic == 1)
    ++magic;
  return magic;
}


/* Visualize the chunk as being partitioned into blocks of 255 bytes from the
   highest address of the chunk, downwards.  The end of each block tells
   us the size of that block, up to the actual size of the requested
   memory.  Our magic byte is right at the end of the requested size, so we
   must reach it with this iteration, otherwise we have witnessed a memory
   corruption.  */
static size_t
malloc_check_get_size (mchunkptr p)
{
  size_t size;
  unsigned char c;
  unsigned char magic = magicbyte (p);

  assert (using_malloc_checking == 1);

  for (size = chunksize (p) - 1 + (chunk_is_mmapped (p) ? 0 : SIZE_SZ);
       (c = ((unsigned char *) p)[size]) != magic;
       size -= c)
    {
      if (c <= 0 || size < (c + 2 * SIZE_SZ))
	malloc_printerr ("malloc_check_get_size: memory corruption");
    }

  /* chunk2mem size.  */
  return size - 2 * SIZE_SZ;
}

/* Instrument a chunk with overrun detector byte(s) and convert it
   into a user pointer with requested size req_sz. */

static void *
mem2mem_check (void *ptr, size_t req_sz)
{
  mchunkptr p;
  unsigned char *m_ptr = ptr;
  size_t max_sz, block_sz, i;
  unsigned char magic;

  if (!ptr)
    return ptr;

  p = mem2chunk (ptr);
  magic = magicbyte (p);
  max_sz = chunksize (p) - 2 * SIZE_SZ;
  if (!chunk_is_mmapped (p))
    max_sz += SIZE_SZ;
  for (i = max_sz - 1; i > req_sz; i -= block_sz)
    {
      block_sz = MIN (i - req_sz, 0xff);
      /* Don't allow the magic byte to appear in the chain of length bytes.
         For the following to work, magicbyte cannot return 0x01.  */
      if (block_sz == magic)
        --block_sz;

      m_ptr[i] = block_sz;
    }
  m_ptr[