slab: Avoid race on slab->obj_exts in alloc_slab_obj_exts

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: slab: Avoid race on slab->obj_exts in alloc_slab_obj_exts If two competing threads enter alloc_slab_obj_exts() and one of them fails to allocate the object extension vector, it might override the valid slab->obj_exts allocated by the other thread with OBJEXTS_ALLOC_FAIL. This will cause the thread that lost this race and expects a valid pointer to dereference a NULL pointer later on. Update slab->obj_exts atomically using cmpxchg() to avoid slab->obj_exts overrides by racing threads. Thanks for Vlastimil and Suren's help with debugging.

References

• https://git.kernel.org/stable/c/c7af5300d78460fc5037ddc77113ba3dbfe77dc0
• https://git.kernel.org/stable/c/7c34feda6a9a203c9744281f1b6671b7dad2012d
• https://git.kernel.org/stable/c/6ed8bfd24ce1cb31742b09a3eb557cd008533eec