CVE-2024-47740: f2fs: Require FMODE_WRITE for atomic write ioctls
In the Linux kernel, the following vulnerability has been resolved:
f2fs: Require FMODEWRITE for atomic write ioctls
The F2FS ioctls for starting and committing atomic writes check for inodeownerorcapable(), 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, inodeownerorcapable() 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:
- F2FSIOCSTARTATOMICREPLACE + F2FSIOCCOMMITATOMICWRITE can truncate an inode to size 0 - F2FSIOCSTARTATOMICWRITE + F2FSIOCABORTATOMICWRITE can revert changes another process concurrently made to a file
Fix it by requiring FMODEWRITE for these operations, just like for F2FSIOCMOVERANGE. Since any legitimate caller should only be using these ioctls when intending to write into the file, that seems unlikely to break anything.
Other sources
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— Launchpad
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
debian/linuxto a version that resolves this vulnerability.Fixed in 5.10.234-1Fixed in 6.1.129-1Fixed in 6.1.135-1Fixed in 6.12.25-1Fixed in 6.12.27-1 - Upgrade
Upgrade
debian/linux-6.1to a version that resolves this vulnerability.Fixed in 6.1.129-1~deb11u1 - Configuration
Update the F2FS ioctl access checks for atomic write operations to require FMODE_WRITE, so that LSMs (e.g., SELinux/Landlock) get an opportunity to deny write access; apply the same approach as used for F2FS_IOC_MOVE_RANGE.
Linux kernel (F2FS) Require FMODE_WRITE for atomic write ioctls (F2FS_IOC_START_ATOMIC_WRITE / F2FS_IOC_COMMIT_ATOMIC_WRITE / F2FS_IOC_ABORT_ATOMIC_WRITE) = enabled
Event History
Frequently Asked Questions
What is the severity of CVE-2024-47740?
CVE-2024-47740 has been classified with a medium severity level.
How do I fix CVE-2024-47740?
To fix CVE-2024-47740, update to the patched versions of the Linux kernel: 6.1.123-1, 6.1.119-1, 6.12.11-1, or 6.12.12-1.
What software is affected by CVE-2024-47740?
CVE-2024-47740 affects various versions of the Linux kernel, specifically versions up to 5.10.226-1.
What type of vulnerability is CVE-2024-47740?
CVE-2024-47740 is a security vulnerability associated with the handling of atomic write ioctls in the F2FS file system.
Can CVE-2024-47740 be exploited remotely?
CVE-2024-47740 does not indicate that it is remotely exploitable; it pertains to local file system operations.