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memalign: reinstate alignment overflow check (CVE-2026-0861) 

The change to cap valid sizes to PTRDIFF_MAX inadvertently dropped the
overflow check for alignment in memalign functions, _mid_memalign and
_int_memalign.  Reinstate the overflow check in _int_memalign, aligned
with the PTRDIFF_MAX change since that is directly responsible for the
CVE.  The missing _mid_memalign check is not relevant (and does not have
a security impact) and may need a different approach to fully resolve,
so it has been omitted.

CVE-Id: CVE-2026-0861
Vulnerable-Commit: 9bf8e29ca1
Reported-by: Igor Morgenstern, Aisle Research
Fixes: BZ #33796
Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>
(cherry picked from commit c9188d3337)
This commit is contained in:
Siddhesh Poyarekar 2026-01-15 06:06:40 -05:00
parent 7b8f497fe4
commit 744b63026a
2 changed files with 7 additions and 10 deletions
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7
malloc/malloc.c
View File

@ -5042,7 +5042,7 @@ _int_memalign (mstate av, size_t alignment, size_t bytes)
INTERNAL_SIZE_T size;
nb = checked_request2size (bytes);
if (nb == 0)
if (nb == 0 || alignment > PTRDIFF_MAX)
{
__set_errno (ENOMEM);
return NULL;
@ -5058,7 +5058,10 @@ _int_memalign (mstate av, size_t alignment, size_t bytes)
we don't find anything in those bins, the common malloc code will
scan starting at 2x. */
/* Call malloc with worst case padding to hit alignment. */
/* Call malloc with worst case padding to hit alignment. ALIGNMENT is a
power of 2, so it tops out at (PTRDIFF_MAX >> 1) + 1, leaving plenty of
space to add MINSIZE and whatever checked_request2size adds to BYTES to
get NB. Consequently, total below also does not overflow. */
m = (char *) (_int_malloc (av, nb + alignment + MINSIZE));
if (m == 0)

10
malloc/tst-malloc-too-large.c
View File

@ -152,7 +152,6 @@ test_large_allocations (size_t size)
}
static long pagesize;
/* This function tests the following aligned memory allocation functions
using several valid alignments and precedes each allocation test with a
@ -171,8 +170,8 @@ test_large_aligned_allocations (size_t size)
/* All aligned memory allocation functions expect an alignment that is a
power of 2. Given this, we test each of them with every valid
alignment from 1 thru PAGESIZE. */
for (align = 1; align <= pagesize; align *= 2)
alignment for the type of ALIGN, i.e. until it wraps to 0. */
for (align = 1; align > 0; align <<= 1)
{
test_setup ();
#if __GNUC_PREREQ (7, 0)
@ -265,11 +264,6 @@ do_test (void)
DIAG_IGNORE_NEEDS_COMMENT (7, "-Walloc-size-larger-than=");
#endif
/* Aligned memory allocation functions need to be tested up to alignment
size equivalent to page size, which should be a power of 2. */
pagesize = sysconf (_SC_PAGESIZE);
TEST_VERIFY_EXIT (powerof2 (pagesize));
/* Loop 1: Ensure that all allocations with SIZE close to SIZE_MAX, i.e.
in the range (SIZE_MAX - 2^14, SIZE_MAX], fail.