Subject: CVE-2024-47740: f2fs: Require FMODE_WRITE for atomic write ioctls

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

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

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

f2fs: Require FMODE_WRITE for atomic write ioctls

The F2FS ioctls for starting and committing atomic writes check for
inode_owner_or_capable(), but this does not give LSMs like SELinux or
Landlock an opportunity to deny the write access - if the caller's FSUID
matches the inode's UID, inode_owner_or_capable() immediately returns true.

There are scenarios where LSMs want to deny a process the ability to write
particular files, even files that the FSUID of the process owns; but this
can currently partially be bypassed using atomic write ioctls in two ways:

 - F2FS_IOC_START_ATOMIC_REPLACE + F2FS_IOC_COMMIT_ATOMIC_WRITE can
   truncate an inode to size 0
 - F2FS_IOC_START_ATOMIC_WRITE + F2FS_IOC_ABORT_ATOMIC_WRITE can revert
   changes another process concurrently made to a file

Fix it by requiring FMODE_WRITE for these operations, just like for
F2FS_IOC_MOVE_RANGE. Since any legitimate caller should only be using these
ioctls when intending to write into the file, that seems unlikely to break
anything.

The Linux kernel CVE team has assigned CVE-2024-47740 to this issue.

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

	Issue introduced in 3.18 with commit 88b88a667971 and fixed in 5.10.227 with commit 000bab8753ae
	Issue introduced in 3.18 with commit 88b88a667971 and fixed in 5.15.168 with commit 88ff021e1fea
	Issue introduced in 3.18 with commit 88b88a667971 and fixed in 6.1.113 with commit 32f348ecc149
	Issue introduced in 3.18 with commit 88b88a667971 and fixed in 6.6.54 with commit 5e0de753bfe8
	Issue introduced in 3.18 with commit 88b88a667971 and fixed in 6.10.13 with commit f3bfac2cabf5
	Issue introduced in 3.18 with commit 88b88a667971 and fixed in 6.11.2 with commit 4583290898c1
	Issue introduced in 3.18 with commit 88b88a667971 and fixed in 6.12-rc1 with commit 4f5a100f87f3

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-2024-47740
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/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/000bab8753ae29a259feb339b99ee759795a48ac
	https://git.kernel.org/stable/c/88ff021e1fea2d9b40b2d5efd9013c89f7be04ac
	https://git.kernel.org/stable/c/32f348ecc149e9ca70a1c424ae8fa9b6919d2713
	https://git.kernel.org/stable/c/5e0de753bfe87768ebe6744d869caa92f35e5731
	https://git.kernel.org/stable/c/f3bfac2cabf5333506b263bc0c8497c95302f32d
	https://git.kernel.org/stable/c/4583290898c13c2c2e5eb8773886d153c2c5121d
	https://git.kernel.org/stable/c/4f5a100f87f32cb65d4bb1ad282a08c92f6f591e