CVE-2021-47221

In the Linux kernel, the following vulnerability has been resolved:
mm/slub: actually fix freelist pointer vs redzoning It turns out that SLUB
redzoning (“slub_debug=Z”) checks from s->object_size rather than from
s->inuse (which is normally bumped to make room for the freelist pointer),
so a cache created with an object size less than 24 would have the freelist
pointer written beyond s->object_size, causing the redzone to be corrupted
by the freelist pointer. This was very visible with “slub_debug=ZF”: BUG
test (Tainted: G B ): Right Redzone overwritten

INFO: 0xffff957ead1c05de-0xffff957ead1c05df @offset=1502. First byte 0x1a
instead of 0xbb INFO: Slab 0xffffef3950b47000 objects=170 used=170
fp=0x0000000000000000 flags=0x8000000000000200 INFO: Object
0xffff957ead1c05d8 @offset=1496 fp=0xffff957ead1c0620 Redzone
(ptrval): bb bb bb bb bb bb bb bb … Object (ptrval):
00 00 00 00 00 f6 f4 a5 … Redzone (ptrval): 40 1d e8 1a aa
@… Padding (ptrval): 00 00 00 00 00 00 00 00 … Adjust the
offset to stay within s->object_size. (Note that no caches of in this size
range are known to exist in the kernel currently.)