CVE-2026-23233 f2fs: fix to avoid mapping wrong physical block for swapfile
A flaw in the Linux kernel F2FS filesystem causes incorrect physical block mapping for small swapfiles, leading to data corruption and system crashes.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23233?
CVE-2026-23233 is a high-severity memory corruption vulnerability in Linux kernel, published on 4 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix to avoid mapping wrong physical block for swapfile
Xiaolong Guo reported a f2fs bug in bugzilla [1]
[1] https://bugzilla.kernel.org/show_bug.cgi?id=220951
Quoted:
"When using stress-ng's swap stress test on F2FS filesystem with kernel 6.6+, the system experiences data corruption leading to either: 1 dm-verity corruption errors and device reboot 2 F2FS node corruption errors and boot hangs
The issue occurs specifically when: 1 Using F2FS filesystem (ext4 is unaffected) 2 Swapfile size is less than F2FS section size (2MB) 3 Swapfile has fragmented physical layout (multiple non-contiguous extents) 4 Kernel version is 6.6+ (6.1 is unaffected)
The root cause is in check_swap_activate() function in fs/f2fs/data.c. When the first extent of a small swapfile (< 2MB) is not aligned to section boundaries, the function incorrectly treats it as the last extent, failing to map subsequent extents. This results in incorrect swap_extent creation where only the first extent is mapped, causing subsequent swap writes to overwrite wrong physical locations (other files' data).
Steps to Reproduce 1 Setup a device with F2FS-formatted userdata partition 2 Compile stress-ng from https://github.com/ColinIanKing/stress-ng 3 Run swap stress test: (Android devices) adb shell "cd /data/stressng; ./stress-ng-64 --metrics-brief --timeout 60 --swap 0"
Log: 1 Ftrace shows in kernel 6.6, only first extent is mapped during second f2fs_map_blocks call in check_swap_activate(): stress-ng-swap-8990: f2fs_map_blocks: ino=11002, file offset=0, start blkaddr=0x43143, len=0x1 (Only 4KB mapped, not the full swapfile) 2 in kernel 6.1, both extents are correctly mapped: stress-ng-swap-5966: f2fs_map_blocks: ino=28011, file offset=0, start blkaddr=0x13cd4, len=0x1 stress-ng-swap-5966: f2fs_map_blocks: ino=28011, file offset=1, start blkaddr=0x60c84b, len=0xff
The problematic code is in check_swap_activate(): if ((pblock - SM_I(sbi)->main_blkaddr) % blks_per_sec || nr_pblocks % blks_per_sec || !f2fs_valid_pinned_area(sbi, pblock)) { bool last_extent = false;
not_aligned++;
nr_pblocks = roundup(nr_pblocks, blks_per_sec); if (cur_lblock + nr_pblocks > sis->max) nr_pblocks -= blks_per_sec;
/* this extent is last one */ if (!nr_pblocks) { nr_pblocks = last_lblock - cur_lblock; last_extent = true; }
ret = f2fs_migrate_blocks(inode, cur_lblock, nr_pblocks); if (ret) { if (ret == -ENOENT) ret = -EINVAL; goto out; }
if (!last_extent) goto retry; }
When the first extent is unaligned and roundup(nr_pblocks, blks_per_sec) exceeds sis->max, we subtract blks_per_sec resulting in nr_pblocks = 0. The code then incorrectly assumes this is the last extent, sets nr_pblocks = last_lblock - cur_lblock (entire swapfile), and performs migration. After migration, it doesn't retry mapping, so subsequent extents are never processed. "
In order to fix this issue, we need to lookup block mapping info after we migrate all blocks in the tail of swapfile.
Weakness: CWE-787
Which versions are affected by CVE-2026-23233?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-23233?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-23233 being exploited?
There is no known exploitation of CVE-2026-23233 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-23233, DEBIAN-CVE-2026-23233, GHSA-p99w-mp33-jg8x, ROOT-OS-DEBIAN-13-CVE-2026-23233, ROOT-OS-UBUNTU-2404-CVE-2026-23233, UBUNTU-CVE-2026-23233.