Subject: CVE-2022-48984: can: slcan: fix freed work crash

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

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

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

can: slcan: fix freed work crash

The LTP test pty03 is causing a crash in slcan:
  BUG: kernel NULL pointer dereference, address: 0000000000000008
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: 0000 [#1] PREEMPT SMP NOPTI
  CPU: 0 PID: 348 Comm: kworker/0:3 Not tainted 6.0.8-1-default #1 openSUSE Tumbleweed 9d20364b934f5aab0a9bdf84e8f45cfdfae39dab
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014
  Workqueue:  0x0 (events)
  RIP: 0010:process_one_work (/home/rich/kernel/linux/kernel/workqueue.c:706 /home/rich/kernel/linux/kernel/workqueue.c:2185)
  Code: 49 89 ff 41 56 41 55 41 54 55 53 48 89 f3 48 83 ec 10 48 8b 06 48 8b 6f 48 49 89 c4 45 30 e4 a8 04 b8 00 00 00 00 4c 0f 44 e0 <49> 8b 44 24 08 44 8b a8 00 01 00 00 41 83 e5 20 f6 45 10 04 75 0e
  RSP: 0018:ffffaf7b40f47e98 EFLAGS: 00010046
  RAX: 0000000000000000 RBX: ffff9d644e1b8b48 RCX: ffff9d649e439968
  RDX: 00000000ffff8455 RSI: ffff9d644e1b8b48 RDI: ffff9d64764aa6c0
  RBP: ffff9d649e4335c0 R08: 0000000000000c00 R09: ffff9d64764aa734
  R10: 0000000000000007 R11: 0000000000000001 R12: 0000000000000000
  R13: ffff9d649e4335e8 R14: ffff9d64490da780 R15: ffff9d64764aa6c0
  FS:  0000000000000000(0000) GS:ffff9d649e400000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000008 CR3: 0000000036424000 CR4: 00000000000006f0
  Call Trace:
   <TASK>
  worker_thread (/home/rich/kernel/linux/kernel/workqueue.c:2436)
  kthread (/home/rich/kernel/linux/kernel/kthread.c:376)
  ret_from_fork (/home/rich/kernel/linux/arch/x86/entry/entry_64.S:312)

Apparently, the slcan's tx_work is freed while being scheduled. While
slcan_netdev_close() (netdev side) calls flush_work(&sl->tx_work),
slcan_close() (tty side) does not. So when the netdev is never set UP,
but the tty is stuffed with bytes and forced to wakeup write, the work
is scheduled, but never flushed.

So add an additional flush_work() to slcan_close() to be sure the work
is flushed under all circumstances.

The Fixes commit below moved flush_work() from slcan_close() to
slcan_netdev_close(). What was the rationale behind it? Maybe we can
drop the one in slcan_netdev_close()?

I see the same pattern in can327. So it perhaps needs the very same fix.

The Linux kernel CVE team has assigned CVE-2022-48984 to this issue.

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

	Issue introduced in 6.0 with commit cfcb4465e992 and fixed in 6.0.13 with commit 9e2709d58a14
	Issue introduced in 6.0 with commit cfcb4465e992 and fixed in 6.1 with commit fb855e9f3b6b

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-2022-48984
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:
	drivers/net/can/slcan/slcan-core.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/9e2709d58a14a10eb00d919acd7dec071c33f8c8
	https://git.kernel.org/stable/c/fb855e9f3b6b42c72af3f1eb0b288998fe0d5ebb