Subject: CVE-2021-47353: udf: Fix NULL pointer dereference in udf_symlink function

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

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

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

udf: Fix NULL pointer dereference in udf_symlink function

In function udf_symlink, epos.bh is assigned with the value returned
by udf_tgetblk. The function udf_tgetblk is defined in udf/misc.c
and returns the value of sb_getblk function that could be NULL.
Then, epos.bh is used without any check, causing a possible
NULL pointer dereference when sb_getblk fails.

This fix adds a check to validate the value of epos.bh.

The Linux kernel CVE team has assigned CVE-2021-47353 to this issue.

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

	Fixed in 4.4.276 with commit 2f3d9ddd32a2
	Fixed in 4.9.276 with commit 371566f63cbd
	Fixed in 4.14.240 with commit baea588a42d6
	Fixed in 4.19.198 with commit 3638705ecd5a
	Fixed in 5.4.133 with commit 80d505aee639
	Fixed in 5.10.51 with commit 21bf1414580c
	Fixed in 5.12.18 with commit aebed6b19e51
	Fixed in 5.13.3 with commit 5150877e4d99
	Fixed in 5.14 with commit fa236c2b2d44

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-2021-47353
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:
	fs/udf/namei.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/2f3d9ddd32a28803baa547e6274983b67d5e287c
	https://git.kernel.org/stable/c/371566f63cbd0bb6fbb25b8fe9d5798268d35af9
	https://git.kernel.org/stable/c/baea588a42d675e35daeaddd10fbc9700550bc4d
	https://git.kernel.org/stable/c/3638705ecd5ad2785e996f820121c0ad15ce64b5
	https://git.kernel.org/stable/c/80d505aee6398cf8beb72475c7edcf1733c1c68b
	https://git.kernel.org/stable/c/21bf1414580c36ffc8d8de043beb3508cf812238
	https://git.kernel.org/stable/c/aebed6b19e51a34003d998da5ebb1dfdd2cb1d02
	https://git.kernel.org/stable/c/5150877e4d99f85057a458daac7cd7c01005d5c6
	https://git.kernel.org/stable/c/fa236c2b2d4436d9f19ee4e5d5924e90ffd7bb43