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

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.

Classification

CVE ID: CVE-2024-47740

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.18% (probability of being exploited)

EPSS Percentile: 39.94% (scored less or equal to compared to others)

EPSS Date: 2025-05-28 (when was this score calculated)

Stakeholder-Specific Vulnerability Categorization (SSVC)

SSVC Exploitation: none

SSVC Technical Impact: partial

SSVC Automatable: false

References

https://nvd.nist.gov/vuln/detail/CVE-2024-47740
https://git.kernel.org/stable/c/700f3a7c7fa5764c9f24bbf7c78e0b6e479fa653
https://git.kernel.org/stable/c/4ce87674c3a6b4d3b3d45f85b584ab8618a3cece
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

Timeline