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changeset: 84522:549d8d3297f2 user: Victor Stinner victor.stinner@gmail.com date: Tue Jul 09 00:44:43 2013 +0200 files: Objects/obmalloc.c description: Issue #18408: Fix _PyMem_DebugRealloc() Don't mark old extra memory dead before calling realloc(). realloc() can fail and realloc() must not touch the original buffer on failure. So mark old extra memory dead only on success if the new buffer did not move (has the same address). diff -r d605c6b8095c -r 549d8d3297f2 Objects/obmalloc.c --- a/Objects/obmalloc.c Tue Jul 09 00:37:24 2013 +0200 +++ b/Objects/obmalloc.c Tue Jul 09 00:44:43 2013 +0200 @@ -1780,7 +1780,7 @@ _PyMem_DebugRealloc(void *ctx, void *p, size_t nbytes) { debug_alloc_api_t *api = (debug_alloc_api_t *)ctx; - uchar *q = (uchar *)p; + uchar *q = (uchar *)p, *oldq; uchar *tail; size_t total; /* nbytes + 4*SST */ size_t original_nbytes; @@ -1797,24 +1797,26 @@ /* overflow: can't represent total as a size_t */ return NULL; - if (nbytes < original_nbytes) { - /* shrinking: mark old extra memory dead */ - memset(q + nbytes, DEADBYTE, original_nbytes - nbytes + 2*SST); - } - /* 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; q = (uchar *)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] == (uchar)api->api_id); for (i = 1; i < SST; ++i) assert(q[SST + i] == FORBIDDENBYTE); q += 2*SST; + tail = q + nbytes; memset(tail, FORBIDDENBYTE, SST); write_size_t(tail + SST, serialno); /victor.stinner@gmail.com