Subject: CVE-2022-48649: mm/slab_common: fix possible double free of kmem_cache

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

mm/slab_common: fix possible double free of kmem_cache

When doing slub_debug test, kfence's 'test_memcache_typesafe_by_rcu'
kunit test case cause a use-after-free error:

  BUG: KASAN: use-after-free in kobject_del+0x14/0x30
  Read of size 8 at addr ffff888007679090 by task kunit_try_catch/261

  CPU: 1 PID: 261 Comm: kunit_try_catch Tainted: G    B            N 6.0.0-rc5-next-20220916 #17
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
  Call Trace:
   <TASK>
   dump_stack_lvl+0x34/0x48
   print_address_description.constprop.0+0x87/0x2a5
   print_report+0x103/0x1ed
   kasan_report+0xb7/0x140
   kobject_del+0x14/0x30
   kmem_cache_destroy+0x130/0x170
   test_exit+0x1a/0x30
   kunit_try_run_case+0xad/0xc0
   kunit_generic_run_threadfn_adapter+0x26/0x50
   kthread+0x17b/0x1b0
   </TASK>

The cause is inside kmem_cache_destroy():

kmem_cache_destroy
    acquire lock/mutex
    shutdown_cache
        schedule_work(kmem_cache_release) (if RCU flag set)
    release lock/mutex
    kmem_cache_release (if RCU flag not set)

In some certain timing, the scheduled work could be run before
the next RCU flag checking, which can then get a wrong value
and lead to double kmem_cache_release().

Fix it by caching the RCU flag inside protected area, just like 'refcnt'

The Linux kernel CVE team has assigned CVE-2022-48649 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.19.8 with commit 357321557920 and fixed in 5.19.12 with commit c673c6ceac53

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2022-48649
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	mm/slab_common.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/c673c6ceac53fb2e631c9fbbd79957099a08927f
	https://git.kernel.org/stable/c/d71608a877362becdc94191f190902fac1e64d35