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bpo-31626: Fixed a bug in debug memory allocator. (GH-3844) (#4191)

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Removed a code that incorrectly detected in-place resizing in realloc()
 and wrote to freed memory.
(cherry picked from commit b484d5606c)
This commit is contained in:
Miss Islington (bot) 2017-10-31 06:58:33 -07:00 • committed by Serhiy Storchaka
parent f9a639b97c
commit ece5659565
2 changed files with 4 additions and 11 deletions
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2
Misc/NEWS.d/next/Core and Builtins/2017-10-01-15-48-03.bpo-31626.reLPxY.rst Normal file
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@ -0,0 +1,2 @@
Fixed a bug in debug memory allocator. There was a write to freed memory
after shrinking a memory block.

13
Objects/obmalloc.c
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@ -1914,7 +1914,7 @@ static void *
_PyMem_DebugRawRealloc(void *ctx, void *p, size_t nbytes) _PyMem_DebugRawRealloc(void *ctx, void *p, size_t nbytes)
{ {
debug_alloc_api_t *api = (debug_alloc_api_t *)ctx; debug_alloc_api_t *api = (debug_alloc_api_t *)ctx;
uint8_t *q = (uint8_t *)p, *oldq; uint8_t *q = (uint8_t *)p;
uint8_t *tail; uint8_t *tail;
size_t total; /* nbytes + 4*SST */ size_t total; /* nbytes + 4*SST */
size_t original_nbytes; size_t original_nbytes;
@ -1931,20 +1931,11 @@ _PyMem_DebugRawRealloc(void *ctx, void *p, size_t nbytes)
/* overflow: can't represent total as a Py_ssize_t */ /* overflow: can't represent total as a Py_ssize_t */
return NULL; return NULL;
/* Resize and add decorations. We may get a new pointer here, in which /* Resize and add decorations. */
* case we didn't get the chance to mark the old memory with DEADBYTE,
* but we live with that.
*/
oldq = q;
q = (uint8_t *)api->alloc.realloc(api->alloc.ctx, q - 2*SST, total); q = (uint8_t *)api->alloc.realloc(api->alloc.ctx, q - 2*SST, total);
if (q == NULL) if (q == NULL)
return NULL; return NULL;
if (q == oldq && nbytes < original_nbytes) {
/* shrinking: mark old extra memory dead */
memset(q + nbytes, DEADBYTE, original_nbytes - nbytes);
}
write_size_t(q, nbytes); write_size_t(q, nbytes);
assert(q[SST] == (uint8_t)api->api_id); assert(q[SST] == (uint8_t)api->api_id);
for (i = 1; i < SST; ++i) for (i = 1; i < SST; ++i)