f2fs: Require FMODE_WRITE for atomic write ioctls

Summary

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.

Timeline

1. Oct 21, 2024, 12:14 PM UTCCVE published
2. Oct 21, 2024, 12:59 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Aug 5, 2026, 11:39 AM UTCRecord last updated

Affected versions

• Linux Linux

  Version range not reported

• Linux Linux

  3.18

References 9