Subject: CVE-2024-40966: tty: add the option to have a tty reject a new ldisc

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

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

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

tty: add the option to have a tty reject a new ldisc

... and use it to limit the virtual terminals to just N_TTY.  They are
kind of special, and in particular, the "con_write()" routine violates
the "writes cannot sleep" rule that some ldiscs rely on.

This avoids the

   BUG: sleeping function called from invalid context at kernel/printk/printk.c:2659

when N_GSM has been attached to a virtual console, and gsmld_write()
calls con_write() while holding a spinlock, and con_write() then tries
to get the console lock.

The Linux kernel CVE team has assigned CVE-2024-40966 to this issue.

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

	Fixed in 6.1.96 with commit 3c6332f3bb15
	Fixed in 6.6.36 with commit 287b569a5b91
	Fixed in 6.9.7 with commit 5920ac19964f
	Fixed in 6.10 with commit 6bd23e0c2bb6

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-2024-40966
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/tty_ldisc.c
	drivers/tty/vt/vt.c
	include/linux/tty_driver.h

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/3c6332f3bb1578b5b10ac2561247b1d6272ae937
	https://git.kernel.org/stable/c/287b569a5b914903ba7c438a3c0dbc3410ebb409
	https://git.kernel.org/stable/c/5920ac19964f9e20181f63b410d9200ddbf8dc86
	https://git.kernel.org/stable/c/6bd23e0c2bb6c65d4f5754d1456bc9a4427fc59b