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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
for small chunk sizes.  The ncopies variable has the wrong type, and
an integer wraparound could cause the existing code to copy too few
elements (leaving the new memory region mostly uninitialized).
Therefore, removing this code fixes bug 24027.

(cherry picked from commit b50dd3bc8c)
This commit is contained in:
Florian Weimer 2018-12-31 22:04:36 +01:00
parent a0bc5dd3be
commit 94417f6c26
3 changed files with 9 additions and 42 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2018-12-31 Florian Weimer <fw@deneb.enyo.de>
[BZ #24027]
* malloc/malloc.c (_int_realloc): Always call memcpy for the
copying operation. (ncopies had the wrong type, resulting in an
integer wraparound and too few elements being copied.)
2018-11-27 Florian Weimer <fweimer@redhat.com>
[BZ #23927]

1
NEWS
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@ -163,6 +163,7 @@ The following bugs are resolved with this release:
[23579] libc: Errors misreported in preadv2
[23709] Fix CPU string flags for Haswell-type CPUs
[23927] Linux if_nametoindex() does not close descriptor (CVE-2018-19591)
[24027] malloc: Integer overflow in realloc
Version 2.26

43
malloc/malloc.c
View File

@ -4528,11 +4528,6 @@ _int_realloc(mstate av, mchunkptr oldp, INTERNAL_SIZE_T oldsize,
mchunkptr bck; /* misc temp for linking */
mchunkptr fwd; /* misc temp for linking */
unsigned long copysize; /* bytes to copy */
unsigned int ncopies; /* INTERNAL_SIZE_T words to copy */
INTERNAL_SIZE_T* s; /* copy source */
INTERNAL_SIZE_T* d; /* copy destination */
/* oldmem size */
if (__builtin_expect (chunksize_nomask (oldp) <= 2 * SIZE_SZ, 0)
|| __builtin_expect (oldsize >= av->system_mem, 0))
@ -4600,43 +4595,7 @@ _int_realloc(mstate av, mchunkptr oldp, INTERNAL_SIZE_T oldsize,
}
else
{
/*
Unroll copy of <= 36 bytes (72 if 8byte sizes)
We know that contents have an odd number of
INTERNAL_SIZE_T-sized words; minimally 3.
*/
copysize = oldsize - SIZE_SZ;
s = (INTERNAL_SIZE_T *) (chunk2mem (oldp));
d = (INTERNAL_SIZE_T *) (newmem);
ncopies = copysize / sizeof (INTERNAL_SIZE_T);
assert (ncopies >= 3);
if (ncopies > 9)
memcpy (d, s, copysize);
else
{
*(d + 0) = *(s + 0);
*(d + 1) = *(s + 1);
*(d + 2) = *(s + 2);
if (ncopies > 4)
{
*(d + 3) = *(s + 3);
*(d + 4) = *(s + 4);
if (ncopies > 6)
{
*(d + 5) = *(s + 5);
*(d + 6) = *(s + 6);
if (ncopies > 8)
{
*(d + 7) = *(s + 7);
*(d + 8) = *(s + 8);
}
}
}
}
memcpy (newmem, chunk2mem (oldp), oldsize - SIZE_SZ);
_int_free (av, oldp, 1);
check_inuse_chunk (av, newp);
return chunk2mem (newp);