linux-cve-announce - CVE-2024-36016: tty: n_gsm: fix possible out-of-bounds in gsm0

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Message-ID: <2024052947-CVE-2024-36016-d30a@gregkh>
Date: Wed, 29 May 2024 20:46:48 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-36016: tty: n_gsm: fix possible out-of-bounds in gsm0_receive()

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

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

tty: n_gsm: fix possible out-of-bounds in gsm0_receive()

Assuming the following:
- side A configures the n_gsm in basic option mode
- side B sends the header of a basic option mode frame with data length 1
- side A switches to advanced option mode
- side B sends 2 data bytes which exceeds gsm->len
  Reason: gsm->len is not used in advanced option mode.
- side A switches to basic option mode
- side B keeps sending until gsm0_receive() writes past gsm->buf
  Reason: Neither gsm->state nor gsm->len have been reset after
  reconfiguration.

Fix this by changing gsm->count to gsm->len comparison from equal to less
than. Also add upper limit checks against the constant MAX_MRU in
gsm0_receive() and gsm1_receive() to harden against memory corruption of
gsm->len and gsm->mru.

All other checks remain as we still need to limit the data according to the
user configuration and actual payload size.

The Linux kernel CVE team has assigned CVE-2024-36016 to this issue.


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

	Issue introduced in 2.6.35 with commit e1eaea46bb40 and fixed in 6.10-rc1 with commit 47388e807f85

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-2024-36016
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/47388e807f85948eefc403a8a5fdc5b406a65d5a