Subject: CVE-2021-47114: ocfs2: fix data corruption by fallocate

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

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

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

ocfs2: fix data corruption by fallocate

When fallocate punches holes out of inode size, if original isize is in
the middle of last cluster, then the part from isize to the end of the
cluster will be zeroed with buffer write, at that time isize is not yet
updated to match the new size, if writeback is kicked in, it will invoke
ocfs2_writepage()->block_write_full_page() where the pages out of inode
size will be dropped.  That will cause file corruption.  Fix this by
zero out eof blocks when extending the inode size.

Running the following command with qemu-image 4.2.1 can get a corrupted
coverted image file easily.

    qemu-img convert -p -t none -T none -f qcow2 $qcow_image \
             -O qcow2 -o compat=1.1 $qcow_image.conv

The usage of fallocate in qemu is like this, it first punches holes out
of inode size, then extend the inode size.

    fallocate(11, FALLOC_FL_KEEP_SIZE|FALLOC_FL_PUNCH_HOLE, 2276196352, 65536) = 0
    fallocate(11, 0, 2276196352, 65536) = 0

v1: https://www.spinics.net/lists/linux-fsdevel/msg193999.html
v2: https://lore.kernel.org/linux-fsdevel/[email-masked]/T/

The Linux kernel CVE team has assigned CVE-2021-47114 to this issue.

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

	Fixed in 4.4.272 with commit 624fa7baa378
	Fixed in 4.9.272 with commit 33e03adafb29
	Fixed in 4.14.236 with commit a1700479524b
	Fixed in 4.19.194 with commit cec4e857ffaa
	Fixed in 5.4.125 with commit cc2edb99ea60
	Fixed in 5.10.43 with commit c8d5faee4624
	Fixed in 5.12.10 with commit 0a31dd6fd2f4
	Fixed in 5.13 with commit 6bba4471f0cc

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-2021-47114
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/ocfs2/file.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/624fa7baa3788dc9e57840ba5b94bc22b03cda57
	https://git.kernel.org/stable/c/33e03adafb29eedae1bae9cdb50c1385279fcf65
	https://git.kernel.org/stable/c/a1700479524bb9cb5e8ae720236a6fabd003acae
	https://git.kernel.org/stable/c/cec4e857ffaa8c447f51cd8ab4e72350077b6770
	https://git.kernel.org/stable/c/cc2edb99ea606a45182b5ea38cc8f4e583aa0774
	https://git.kernel.org/stable/c/c8d5faee46242c3f33b8a71a4d7d52214785bfcc
	https://git.kernel.org/stable/c/0a31dd6fd2f4e7db538fb6eb1f06973d81f8dd3b
	https://git.kernel.org/stable/c/6bba4471f0cc1296fe3c2089b9e52442d3074b2e