CVE-2022-48989

In the Linux kernel, the following vulnerability has been resolved:

fscache: Fix oops due to race with cookie_lru and use_cookie

If a cookie expires from the LRU and the LRU_DISCARD flag is set, but

the state machine has not run yet, it's possible another thread can call

fscache_use_cookie and begin to use it.

When the cookie_worker finally runs, it will see the LRU_DISCARD flag

set, transition the cookie->state to LRU_DISCARDING, which will then

withdraw the cookie. Once the cookie is withdrawn the object is removed

the below oops will occur because the object associated with the cookie

is now NULL.

Fix the oops by clearing the LRU_DISCARD bit if another thread uses the

cookie before the cookie_worker runs.

BUG: kernel NULL pointer dereference, address: 0000000000000008

...

CPU: 31 PID: 44773 Comm: kworker/u130:1 Tainted: G E 6.0.0-5.dneg.x86_64 #1

Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022

Workqueue: events_unbound netfs_rreq_write_to_cache_work [netfs]

RIP: 0010:cachefiles_prepare_write+0x28/0x90 [cachefiles]

...

Call Trace:

netfs_rreq_write_to_cache_work+0x11c/0x320 [netfs]

process_one_work+0x217/0x3e0

worker_thread+0x4a/0x3b0

kthread+0xd6/0x100