CVE-2024-47740 Information

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.

Reference

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