Subject: CVE-2023-52872: tty: n_gsm: fix race condition in status line change on dead connections

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

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

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

tty: n_gsm: fix race condition in status line change on dead connections

gsm_cleanup_mux() cleans up the gsm by closing all DLCIs, stopping all
timers, removing the virtual tty devices and clearing the data queues.
This procedure, however, may cause subsequent changes of the virtual modem
status lines of a DLCI. More data is being added the outgoing data queue
and the deleted kick timer is restarted to handle this. At this point many
resources have already been removed by the cleanup procedure. Thus, a
kernel panic occurs.

Fix this by proving in gsm_modem_update() that the cleanup procedure has
not been started and the mux is still alive.

Note that writing to a virtual tty is already protected by checks against
the DLCI specific connection state.

The Linux kernel CVE team has assigned CVE-2023-52872 to this issue.

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

	Issue introduced in 5.15.61 with commit dd37f6573878 and fixed in 5.15.138 with commit 81a4dd5e6c78
	Issue introduced in 6.0 with commit c568f7086c6e and fixed in 6.1.62 with commit df6cfab66ff2
	Issue introduced in 6.0 with commit c568f7086c6e and fixed in 6.5.11 with commit 19d34b73234a
	Issue introduced in 6.0 with commit c568f7086c6e and fixed in 6.6.1 with commit ce4df90333c4
	Issue introduced in 6.0 with commit c568f7086c6e and fixed in 6.7 with commit 3a75b205de43
	Issue introduced in 5.18.18 with commit d834aba5f30d
	Issue introduced in 5.19.2 with commit 692e847a8e66

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-2023-52872
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/tty/n_gsm.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/81a4dd5e6c78f5d8952fa8c9d36565db1fe01444
	https://git.kernel.org/stable/c/df6cfab66ff2a44bd23ad5dd5309cb3421bb6593
	https://git.kernel.org/stable/c/19d34b73234af542cc8a218cf398dee73cdb1890
	https://git.kernel.org/stable/c/ce4df90333c4fe65acb8b5089fdfe9b955ce976a
	https://git.kernel.org/stable/c/3a75b205de43365f80a33b98ec9289785da56243