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bpo-31626: Fixed a bug in debug memory allocator. #3844

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Merged
serhiy-storchaka merged 4 commits into from
Oct 31, 2017
Merged

bpo-31626: Fixed a bug in debug memory allocator. #3844

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84d97fa
bpo-31626: Fixed a bug in debug memory allocator.
serhiy-storchaka Oct 1, 2017
ccc9501
Removed Py_FatalError().
serhiy-storchaka Oct 2, 2017
f45164b
Merge branch 'master' into debug-realloc-deadbytes
serhiy-storchaka Oct 29, 2017
e228d0a
Don't mark dead bytes in realloc(),
serhiy-storchaka Oct 29, 2017
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2017-10-01-15-48-03.bpo-31626.reLPxY.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fixed a bug in debug memory allocator. There was a write to freed memory
after shrinking a memory block.
13 changes: 2 additions & 11 deletions Objects/obmalloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1460,7 +1460,7 @@ static void *
_PyMem_DebugRawRealloc(void *ctx, void *p, size_t nbytes)
{
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;
size_t total; /* nbytes + 4*SST */
size_t original_nbytes;
Expand All @@ -1477,20 +1477,11 @@ _PyMem_DebugRawRealloc(void *ctx, void *p, size_t nbytes)
/* overflow: can't represent total as a Py_ssize_t */
return NULL;

/* Resize and add decorations. We may get a new pointer here, in which
* case we didn't get the chance to mark the old memory with DEADBYTE,
* but we live with that.
*/
oldq = q;
/* Resize and add decorations. */
q = (uint8_t *)api->alloc.realloc(api->alloc.ctx, q - 2*SST, total);
if (q == 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);
assert(q[SST] == (uint8_t)api->api_id);
for (i = 1; i < SST; ++i)
Expand Down