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/* mcheck debugging hooks for malloc.
Copyright (C) 1990-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
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; if not, see
<https://www.gnu.org/licenses/>. */
#include <malloc-internal.h>
#include <mcheck.h>
#include <libintl.h>
#include <stdint.h>
#include <stdio.h>
/* Arbitrary magical numbers. */
#define MAGICWORD 0xfedabeeb
#define MAGICFREE 0xd8675309
#define MAGICBYTE ((char) 0xd7)
#define MALLOCFLOOD ((char) 0x93)
#define FREEFLOOD ((char) 0x95)
/* Function to call when something awful happens. */
static void (*abortfunc) (enum mcheck_status);
struct hdr
{
size_t size; /* Exact size requested by user. */
unsigned long int magic; /* Magic number to check header integrity. */
struct hdr *prev;
struct hdr *next;
void *block; /* Real block allocated, for memalign. */
unsigned long int magic2; /* Extra, keeps us doubleword aligned. */
} __attribute__ ((aligned (MALLOC_ALIGNMENT)));
/* This is the beginning of the list of all memory blocks allocated.
It is only constructed if the pedantic testing is requested. */
static struct hdr *root;
/* Nonzero if pedentic checking of all blocks is requested. */
static bool pedantic;
#if defined _LIBC || defined STDC_HEADERS || defined USG
# include <string.h>
# define flood memset
#else
static void flood (void *, int, size_t);
static void
flood (void *ptr, int val, size_t size)
{
char *cp = ptr;
while (size--)
*cp++ = val;
}
#endif
static enum mcheck_status
checkhdr (const struct hdr *hdr)
{
enum mcheck_status status;
bool mcheck_used = __is_malloc_debug_enabled (MALLOC_MCHECK_HOOK);
if (!mcheck_used)
/* Maybe the mcheck used is disabled? This happens when we find
an error and report it. */
return MCHECK_OK;
switch (hdr->magic ^ ((uintptr_t) hdr->prev + (uintptr_t) hdr->next))
{
default:
status = MCHECK_HEAD;
break;
case MAGICFREE:
status = MCHECK_FREE;
break;
case MAGICWORD:
if (((char *) &hdr[1])[hdr->size] != MAGICBYTE)
status = MCHECK_TAIL;
else if ((hdr->magic2 ^ (uintptr_t) hdr->block) != MAGICWORD)
status = MCHECK_HEAD;
else
status = MCHECK_OK;
break;
}
if (status != MCHECK_OK)
{
mcheck_used = 0;
(*abortfunc) (status);
mcheck_used = 1;
}
return status;
}
static enum mcheck_status
__mcheck_checkptr (const void *ptr)
{
if (!__is_malloc_debug_enabled (MALLOC_MCHECK_HOOK))
return MCHECK_DISABLED;
if (ptr != NULL)
return checkhdr (((struct hdr *) ptr) - 1);
/* Walk through all the active blocks and test whether they were tampered
with. */
struct hdr *runp = root;
/* Temporarily turn off the checks. */
pedantic = false;
while (runp != NULL)
{
(void) checkhdr (runp);
runp = runp->next;
}
/* Turn checks on again. */
pedantic = true;
return MCHECK_OK;
}
static void
unlink_blk (struct hdr *ptr)
{
if (ptr->next != NULL)
{
ptr->next->prev = ptr->prev;
ptr->next->magic = MAGICWORD ^ ((uintptr_t) ptr->next->prev
+ (uintptr_t) ptr->next->next);
}
if (ptr->prev != NULL)
{
ptr->prev->next = ptr->next;
ptr->prev->magic = MAGICWORD ^ ((uintptr_t) ptr->prev->prev
+ (uintptr_t) ptr->prev->next);
}
else
root = ptr->next;
}
static void
link_blk (struct hdr *hdr)
{
hdr->prev = NULL;
hdr->next = root;
root = hdr;
hdr->magic = MAGICWORD ^ (uintptr_t) hdr->next;
/* And the next block. */
if (hdr->next != NULL)
{
hdr->next->prev = hdr;
hdr->next->magic = MAGICWORD ^ ((uintptr_t) hdr
+ (uintptr_t) hdr->next->next);
}
}
static void *
free_mcheck (void *ptr)
{
if (pedantic)
__mcheck_checkptr (NULL);
if (ptr)
{
struct hdr *hdr = ((struct hdr *) ptr) - 1;
checkhdr (hdr);
hdr->magic = MAGICFREE;
hdr->magic2 = MAGICFREE;
unlink_blk (hdr);
hdr->prev = hdr->next = NULL;
flood (ptr, FREEFLOOD, hdr->size);
ptr = hdr->block;
}
return ptr;
}
static bool
malloc_mcheck_before (size_t *sizep, void **victimp)
{
size_t size = *sizep;
if (pedantic)
__mcheck_checkptr (NULL);
if (size > ~((size_t) 0) - (sizeof (struct hdr) + 1))
{
__set_errno (ENOMEM);
*victimp = NULL;
return true;
}
*sizep = sizeof (struct hdr) + size + 1;
return false;
}
static void *
malloc_mcheck_after (void *mem, size_t size)
{
struct hdr *hdr = mem;
if (hdr == NULL)
return NULL;
hdr->size = size;
link_blk (hdr);
hdr->block = hdr;
hdr->magic2 = (uintptr_t) hdr ^ MAGICWORD;
((char *) &hdr[1])[size] = MAGICBYTE;
flood ((void *) (hdr + 1), MALLOCFLOOD, size);
return (void *) (hdr + 1);
}
static bool
memalign_mcheck_before (size_t alignment, size_t *sizep, void **victimp)
{
struct hdr *hdr;
size_t slop, size = *sizep;
/* Punt to malloc to avoid double headers. */
if (alignment <= MALLOC_ALIGNMENT)
{
*victimp = __debug_malloc (size);
return true;
}
if (pedantic)
__mcheck_checkptr (NULL);
slop = (sizeof *hdr + alignment - 1) & - alignment;
if (size > ~((size_t) 0) - (slop + 1))
{
__set_errno (ENOMEM);
*victimp = NULL;
return true;
}
*sizep = slop + size + 1;
return false;
}
static void *
memalign_mcheck_after (void *block, size_t alignment, size_t size)
{
if (block == NULL)
return NULL;
/* This was served by __debug_malloc, so return as is. */
if (alignment <= MALLOC_ALIGNMENT)
return block;
size_t slop = (sizeof (struct hdr) + alignment - 1) & - alignment;
struct hdr *hdr = ((struct hdr *) (block + slop)) - 1;
hdr->size = size;
link_blk (hdr);
hdr->block = (void *) block;
hdr->magic2 = (uintptr_t) block ^ MAGICWORD;
((char *) &hdr[1])[size] = MAGICBYTE;
flood ((void *) (hdr + 1), MALLOCFLOOD, size);
return (void *) (hdr + 1);
}
static bool
realloc_mcheck_before (void **ptrp, size_t *sizep, size_t *oldsize,
void **victimp)
{
size_t size = *sizep;
void *ptr = *ptrp;
if (ptr == NULL)
{
*victimp = __debug_malloc (size);
*oldsize = 0;
return true;
}
if (size == 0)
{
__debug_free (ptr);
*victimp = NULL;
return true;
}
if (size > ~((size_t) 0) - (sizeof (struct hdr) + 1))
{
__set_errno (ENOMEM);
*victimp = NULL;
*oldsize = 0;
return true;
}
if (pedantic)
__mcheck_checkptr (NULL);
struct hdr *hdr;
size_t osize;
/* Update the oldptr for glibc realloc. */
*ptrp = hdr = ((struct hdr *) ptr) - 1;
osize = hdr->size;
checkhdr (hdr);
unlink_blk (hdr);
if (size < osize)
flood ((char *) ptr + size, FREEFLOOD, osize - size);
*oldsize = osize;
*sizep = sizeof (struct hdr) + size + 1;
return false;
}
static void *
realloc_mcheck_after (void *ptr, void *oldptr, size_t size, size_t osize)
{
struct hdr *hdr = ptr;
if (hdr == NULL)
return NULL;
/* Malloc already added the header so don't tamper with it. */
if (oldptr == NULL)
return ptr;
hdr->size = size;
link_blk (hdr);
hdr->block = hdr;
hdr->magic2 = (uintptr_t) hdr ^ MAGICWORD;
((char *) &hdr[1])[size] = MAGICBYTE;
if (size > osize)
flood ((char *) (hdr + 1) + osize, MALLOCFLOOD, size - osize);
return (void *) (hdr + 1);
}
__attribute__ ((noreturn))
static void
mabort (enum mcheck_status status)
{
const char *msg;
switch (status)
{
case MCHECK_OK:
msg = _ ("memory is consistent, library is buggy\n");
break;
case MCHECK_HEAD:
msg = _ ("memory clobbered before allocated block\n");
break;
case MCHECK_TAIL:
msg = _ ("memory clobbered past end of allocated block\n");
break;
case MCHECK_FREE:
msg = _ ("block freed twice\n");
break;
default:
msg = _ ("bogus mcheck_status, library is buggy\n");
break;
}
#ifdef _LIBC
__libc_fatal (msg);
#else
fprintf (stderr, "mcheck: %s", msg);
fflush (stderr);
abort ();
#endif
}
/* Memory barrier so that GCC does not optimize out the argument. */
#define malloc_opt_barrier(x) \
({ __typeof (x) __x = x; __asm ("" : "+m" (__x)); __x; })
static int
__mcheck_initialize (void (*func) (enum mcheck_status), bool in_pedantic)
{
abortfunc = (func != NULL) ? func : &mabort;
switch (debug_initialized)
{
case -1:
/* Called before the first malloc was called. */
__debug_free (__debug_malloc (0));
/* FALLTHROUGH */
case 0:
/* Called through the initializer hook. */
__malloc_debug_enable (MALLOC_MCHECK_HOOK);
break;
case 1:
default:
/* Malloc was already called. Fail. */
return -1;
}
pedantic = in_pedantic;
return 0;
}
static int
mcheck_usable_size (struct hdr *h)
{
return (h - 1)->size;
}
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