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.)

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.)

En el kernel de Linux, se resolvió la siguiente vulnerabilidad: mm/slub: en realidad corrige el puntero de lista libre frente a redzoning. Resulta que SLUB redzoning ("slub_debug=Z") verifica desde s->object_size en lugar de s->inuse (que normalmente se elimina para dejar espacio para el puntero de lista libre), por lo que un caché creado con un tamaño de objeto menor a 24 tendría el puntero de lista libre escrito más allá de s->object_size, causando que el puntero de lista libre corrompa la zona roja. Esto fue muy visible con "slub_debug=ZF": prueba de BUG(contaminada: GB): zona roja derecha sobrescrita ---------------------------- ------------------------------------------------- INFORMACIÓN : 0xffff957ead1c05de-0xffff957ead1c05df @offset=1502. Primer byte 0x1a en lugar de 0xbb INFORMACIÓN: slab 0xffffef3950b47000 objetos=170 usados=170 fp=0x0000000000000000 banderas=0x80000000000000200 INFORMACIÓN: Objeto 0xffff957ead1c05d8 @offset=1496 fp=0xffff9 57ead1c0620 Zona roja (____ptrval____): bb bb bb bb bb bb bb bb .... .... Objeto (____ptrval____): 00 00 00 00 00 f6 f4 a5 ........ Redzone (____ptrval____): 40 1d e8 1a aa @.... Relleno (____ptrval____): 00 00 00 00 00 00 00 00 ........ Ajuste el desplazamiento para permanecer dentro de s->object_size. (Tenga en cuenta que actualmente no se sabe que existan cachés de este rango de tamaño en el kernel).