Subject: CVE-2021-47004: f2fs: fix to avoid touching checkpointed data in get_victim()

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

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

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

f2fs: fix to avoid touching checkpointed data in get_victim()

In CP disabling mode, there are two issues when using LFS or SSR | AT_SSR
mode to select victim:

1. LFS is set to find source section during GC, the victim should have
no checkpointed data, since after GC, section could not be set free for
reuse.

Previously, we only check valid chpt blocks in current segment rather
than section, fix it.

2. SSR | AT_SSR are set to find target segment for writes which can be
fully filled by checkpointed and newly written blocks, we should never
select such segment, otherwise it can cause panic or data corruption
during allocation, potential case is described as below:

 a) target segment has 'n' (n < 512) ckpt valid blocks
 b) GC migrates 'n' valid blocks to other segment (segment is still
    in dirty list)
 c) GC migrates '512 - n' blocks to target segment (segment has 'n'
    cp_vblocks and '512 - n' vblocks)
 d) If GC selects target segment via {AT,}SSR allocator, however there
    is no free space in targe segment.

The Linux kernel CVE team has assigned CVE-2021-47004 to this issue.

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

	Issue introduced in 4.20 with commit 4354994f097d and fixed in 5.10.38 with commit 105155a8146d
	Issue introduced in 4.20 with commit 4354994f097d and fixed in 5.11.22 with commit 1e116f87825f
	Issue introduced in 4.20 with commit 4354994f097d and fixed in 5.12.5 with commit 211372b25715
	Issue introduced in 4.20 with commit 4354994f097d and fixed in 5.13 with commit 61461fc921b7

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-2021-47004
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/f2fs/f2fs.h
	fs/f2fs/gc.c
	fs/f2fs/segment.c
	fs/f2fs/segment.h

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/105155a8146ddb54c119d8318964eef3859d109d
	https://git.kernel.org/stable/c/1e116f87825f01a6380286472196882746b16f63
	https://git.kernel.org/stable/c/211372b2571520e394b56b431a0705586013b3ff
	https://git.kernel.org/stable/c/61461fc921b756ae16e64243f72af2bfc2e620db