Subject: CVE-2024-35887: ax25: fix use-after-free bugs caused by ax25_ds_del_timer

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

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

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

ax25: fix use-after-free bugs caused by ax25_ds_del_timer

When the ax25 device is detaching, the ax25_dev_device_down()
calls ax25_ds_del_timer() to cleanup the slave_timer. When
the timer handler is running, the ax25_ds_del_timer() that
calls del_timer() in it will return directly. As a result,
the use-after-free bugs could happen, one of the scenarios
is shown below:

      (Thread 1)          |      (Thread 2)
                          | ax25_ds_timeout()
ax25_dev_device_down()    |
  ax25_ds_del_timer()     |
    del_timer()           |
  ax25_dev_put() //FREE   |
                          |  ax25_dev-> //USE

In order to mitigate bugs, when the device is detaching, use
timer_shutdown_sync() to stop the timer.

The Linux kernel CVE team has assigned CVE-2024-35887 to this issue.

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

	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.6.26 with commit 74204bf9050f
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.8.5 with commit c6a368f9c7af
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.9 with commit fd819ad3ecf6

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-2024-35887
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:
	net/ax25/ax25_dev.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/74204bf9050f7627aead9875fe4e07ba125cb19b
	https://git.kernel.org/stable/c/c6a368f9c7af4c14b14d390c2543af8001c9bdb9
	https://git.kernel.org/stable/c/fd819ad3ecf6f3c232a06b27423ce9ed8c20da89