Subject: CVE-2021-47119: ext4: fix memory leak in ext4_fill_super

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

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

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

ext4: fix memory leak in ext4_fill_super

Buffer head references must be released before calling kill_bdev();
otherwise the buffer head (and its page referenced by b_data) will not
be freed by kill_bdev, and subsequently that bh will be leaked.

If blocksizes differ, sb_set_blocksize() will kill current buffers and
page cache by using kill_bdev(). And then super block will be reread
again but using correct blocksize this time. sb_set_blocksize() didn't
fully free superblock page and buffer head, and being busy, they were
not freed and instead leaked.

This can easily be reproduced by calling an infinite loop of:

  systemctl start <ext4_on_lvm>.mount, and
  systemctl stop <ext4_on_lvm>.mount

... since systemd creates a cgroup for each slice which it mounts, and
the bh leak get amplified by a dying memory cgroup that also never
gets freed, and memory consumption is much more easily noticed.

The Linux kernel CVE team has assigned CVE-2021-47119 to this issue.

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

	Issue introduced in 2.6.19 with commit ac27a0ec112a and fixed in 5.10.43 with commit 01d349a481f0
	Issue introduced in 2.6.19 with commit ac27a0ec112a and fixed in 5.12.10 with commit 1385b23396d5
	Issue introduced in 2.6.19 with commit ac27a0ec112a and fixed in 5.13 with commit afd09b617db3

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-2021-47119
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/ext4/super.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/01d349a481f0591230300a9171330136f9159bcd
	https://git.kernel.org/stable/c/1385b23396d511d5233b8b921ac3058b3f86a5e1
	https://git.kernel.org/stable/c/afd09b617db3786b6ef3dc43e28fe728cfea84df