Subject: CVE-2022-48870: tty: fix possible null-ptr-defer in spk_ttyio_release

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

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

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

tty: fix possible null-ptr-defer in spk_ttyio_release

Run the following tests on the qemu platform:

syzkaller:~# modprobe speakup_audptr
 input: Speakup as /devices/virtual/input/input4
 initialized device: /dev/synth, node (MAJOR 10, MINOR 125)
 speakup 3.1.6: initialized
 synth name on entry is: (null)
 synth probe

spk_ttyio_initialise_ldisc failed because tty_kopen_exclusive returned
failed (errno -16), then remove the module, we will get a null-ptr-defer
problem, as follow:

syzkaller:~# modprobe -r speakup_audptr
 releasing synth audptr
 BUG: kernel NULL pointer dereference, address: 0000000000000080
 #PF: supervisor write access in kernel mode
 #PF: error_code(0x0002) - not-present page
 PGD 0 P4D 0
 Oops: 0002 [#1] PREEMPT SMP PTI
 CPU: 2 PID: 204 Comm: modprobe Not tainted 6.1.0-rc6-dirty #1
 RIP: 0010:mutex_lock+0x14/0x30
 Call Trace:
 <TASK>
  spk_ttyio_release+0x19/0x70 [speakup]
  synth_release.part.6+0xac/0xc0 [speakup]
  synth_remove+0x56/0x60 [speakup]
  __x64_sys_delete_module+0x156/0x250
  ? fpregs_assert_state_consistent+0x1d/0x50
  do_syscall_64+0x37/0x90
  entry_SYSCALL_64_after_hwframe+0x63/0xcd
 </TASK>
 Modules linked in: speakup_audptr(-) speakup
 Dumping ftrace buffer:

in_synth->dev was not initialized during modprobe, so we add check
for in_synth->dev to fix this bug.

The Linux kernel CVE team has assigned CVE-2022-48870 to this issue.

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

	Issue introduced in 5.12 with commit 4f2a81f3a882 and fixed in 5.15.90 with commit 2da67bff29ab
	Issue introduced in 5.12 with commit 4f2a81f3a882 and fixed in 6.1.8 with commit 64152e05a4de
	Issue introduced in 5.12 with commit 4f2a81f3a882 and fixed in 6.2 with commit 5abbeebd8296

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-2022-48870
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/accessibility/speakup/spk_ttyio.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/2da67bff29ab49caafb0766e8b8383b735ff796f
	https://git.kernel.org/stable/c/64152e05a4de3ebf59f1740a0985a6d5fba0c77b
	https://git.kernel.org/stable/c/5abbeebd8296c2301023b8dc4b5a6c0d5229b4f5