CVE-2026-43458: serial: caif: hold tty->link reference in ldisc_open and ser_release

CVE-2026-43458: serial: caif: hold tty->link reference in ldisc_open and ser_release

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

serial: caif: hold tty->link reference in ldisc_open and ser_release

A reproducer triggers a KASAN slab-use-after-free in pty_write_room()
when caif_serial's TX path calls tty_write_room(). The faulting access
is on tty->link->port.

Hold an extra kref on tty->link for the lifetime of the caif_serial line
discipline: get it in ldisc_open() and drop it in ser_release(), and
also drop it on the ldisc_open() error path.

With this change applied, the reproducer no longer triggers the UAF in
my testing.

The Linux kernel CVE team has assigned CVE-2026-43458 to this issue.


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

	Issue introduced in 2.6.35 with commit e31d5a05948e4478ba8396063d1e1f39880928e2 and fixed in 5.10.253 with commit 23a3ac2e2262a291498567418227b99e1f3606b1
	Issue introduced in 2.6.35 with commit e31d5a05948e4478ba8396063d1e1f39880928e2 and fixed in 5.15.203 with commit 52135420e9f75853ea0c6cea7b736e3e98495f7d
	Issue introduced in 2.6.35 with commit e31d5a05948e4478ba8396063d1e1f39880928e2 and fixed in 6.1.167 with commit ca2ceba983bb23ea0202c2882d963253416654a3
	Issue introduced in 2.6.35 with commit e31d5a05948e4478ba8396063d1e1f39880928e2 and fixed in 6.6.130 with commit 8460187b4852fd00bd1c76394358053f3fa4d089
	Issue introduced in 2.6.35 with commit e31d5a05948e4478ba8396063d1e1f39880928e2 and fixed in 6.12.78 with commit 27e43356d0defb9fc7fa25265219a3ffeb7b3e98
	Issue introduced in 2.6.35 with commit e31d5a05948e4478ba8396063d1e1f39880928e2 and fixed in 6.18.19 with commit 35b58d3bc716ebb9ebd10fe1cac8c1177242511c
	Issue introduced in 2.6.35 with commit e31d5a05948e4478ba8396063d1e1f39880928e2 and fixed in 6.19.9 with commit 97a0bb491cae39478c6225381f14e9ac67b7bba7
	Issue introduced in 2.6.35 with commit e31d5a05948e4478ba8396063d1e1f39880928e2 and fixed in 7.0 with commit 288598d80a068a0e9281de35bcb4ce495f189e2a

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-2026-43458
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/caif/caif_serial.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/23a3ac2e2262a291498567418227b99e1f3606b1
	https://git.kernel.org/stable/c/52135420e9f75853ea0c6cea7b736e3e98495f7d
	https://git.kernel.org/stable/c/ca2ceba983bb23ea0202c2882d963253416654a3
	https://git.kernel.org/stable/c/8460187b4852fd00bd1c76394358053f3fa4d089
	https://git.kernel.org/stable/c/27e43356d0defb9fc7fa25265219a3ffeb7b3e98
	https://git.kernel.org/stable/c/35b58d3bc716ebb9ebd10fe1cac8c1177242511c
	https://git.kernel.org/stable/c/97a0bb491cae39478c6225381f14e9ac67b7bba7
	https://git.kernel.org/stable/c/288598d80a068a0e9281de35bcb4ce495f189e2a