Subject: CVE-2021-47244: mptcp: Fix out of bounds when parsing TCP options

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

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

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

mptcp: Fix out of bounds when parsing TCP options

The TCP option parser in mptcp (mptcp_get_options) could read one byte
out of bounds. When the length is 1, the execution flow gets into the
loop, reads one byte of the opcode, and if the opcode is neither
TCPOPT_EOL nor TCPOPT_NOP, it reads one more byte, which exceeds the
length of 1.

This fix is inspired by commit 9609dad263f8 ("ipv4: tcp_input: fix stack
out of bounds when parsing TCP options.").

The Linux kernel CVE team has assigned CVE-2021-47244 to this issue.

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

	Issue introduced in 5.6 with commit cec37a6e41aa and fixed in 5.10.46 with commit 73eeba71dc99
	Issue introduced in 5.6 with commit cec37a6e41aa and fixed in 5.12.13 with commit 76e02b8905d0
	Issue introduced in 5.6 with commit cec37a6e41aa and fixed in 5.13 with commit 07718be26568

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-2021-47244
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/mptcp/options.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/73eeba71dc9932970befa009e68272a3d5ec4a58
	https://git.kernel.org/stable/c/76e02b8905d0691e89e104a882f3bba7dd0f6037
	https://git.kernel.org/stable/c/07718be265680dcf496347d475ce1a5442f55ad7