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commit b50dd3bc8cbb1efe85399b03d7e6c0310c2ead84
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Author: Florian Weimer <fw@deneb.enyo.de>
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Date: Mon Dec 31 22:04:36 2018 +0100
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malloc: Always call memcpy in _int_realloc [BZ #24027]
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This commit removes the custom memcpy implementation from _int_realloc
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for small chunk sizes. The ncopies variable has the wrong type, and
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an integer wraparound could cause the existing code to copy too few
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elements (leaving the new memory region mostly uninitialized).
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Therefore, removing this code fixes bug 24027.
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diff -rup a/malloc/malloc.c b/malloc/malloc.c
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--- a/malloc/malloc.c 2019-03-26 14:12:59.364333388 -0400
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+++ b/malloc/malloc.c 2019-03-26 14:17:17.373475418 -0400
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@@ -4214,11 +4214,6 @@ _int_realloc(mstate av, mchunkptr oldp,
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mchunkptr bck; /* misc temp for linking */
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mchunkptr fwd; /* misc temp for linking */
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- unsigned long copysize; /* bytes to copy */
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- unsigned int ncopies; /* INTERNAL_SIZE_T words to copy */
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- INTERNAL_SIZE_T* s; /* copy source */
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- INTERNAL_SIZE_T* d; /* copy destination */
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-
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const char *errstr = NULL;
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/* oldmem size */
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@@ -4291,39 +4286,7 @@ _int_realloc(mstate av, mchunkptr oldp,
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newp = oldp;
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}
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else {
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- /*
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- Unroll copy of <= 36 bytes (72 if 8byte sizes)
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- We know that contents have an odd number of
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- INTERNAL_SIZE_T-sized words; minimally 3.
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- */
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-
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- copysize = oldsize - SIZE_SZ;
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- s = (INTERNAL_SIZE_T*)(chunk2mem(oldp));
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- d = (INTERNAL_SIZE_T*)(newmem);
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- ncopies = copysize / sizeof(INTERNAL_SIZE_T);
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- assert(ncopies >= 3);
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-
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- if (ncopies > 9)
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- MALLOC_COPY(d, s, copysize);
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-
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- else {
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- *(d+0) = *(s+0);
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- *(d+1) = *(s+1);
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- *(d+2) = *(s+2);
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- if (ncopies > 4) {
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- *(d+3) = *(s+3);
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- *(d+4) = *(s+4);
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- if (ncopies > 6) {
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- *(d+5) = *(s+5);
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- *(d+6) = *(s+6);
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- if (ncopies > 8) {
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- *(d+7) = *(s+7);
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- *(d+8) = *(s+8);
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- }
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- }
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- }
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- }
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-
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+ memcpy (newmem, chunk2mem (oldp), oldsize - SIZE_SZ);
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_int_free(av, oldp, 1);
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check_inuse_chunk(av, newp);
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return chunk2mem(newp);
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