CVE-2025-68772 f2fs: fix to avoid updating compression context during writeback
A race condition in the Linux kernel f2fs filesystem allows a local attacker to cause a system crash via divide-by-zero during file writeback.
- 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-2025-68772?
CVE-2025-68772 is a vulnerability in Linux, published on 13 Jan 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 updating compression context during writeback
Bai, Shuangpeng <[email protected]> reported a bug as below:
Oops: divide error: 0000 [#1] SMP KASAN PTI CPU: 0 UID: 0 PID: 11441 Comm: syz.0.46 Not tainted 6.17.0 #1 PREEMPT(full) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:f2fs_all_cluster_page_ready+0x106/0x550 fs/f2fs/compress.c:857 Call Trace: <TASK> f2fs_write_cache_pages fs/f2fs/data.c:3078 [inline] __f2fs_write_data_pages fs/f2fs/data.c:3290 [inline] f2fs_write_data_pages+0x1c19/0x3600 fs/f2fs/data.c:3317 do_writepages+0x38e/0x640 mm/page-writeback.c:2634 filemap_fdatawrite_wbc mm/filemap.c:386 [inline] __filemap_fdatawrite_range mm/filemap.c:419 [inline] file_write_and_wait_range+0x2ba/0x3e0 mm/filemap.c:794 f2fs_do_sync_file+0x6e6/0x1b00 fs/f2fs/file.c:294 generic_write_sync include/linux/fs.h:3043 [inline] f2fs_file_write_iter+0x76e/0x2700 fs/f2fs/file.c:5259 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x7e9/0xe00 fs/read_write.c:686 ksys_write+0x19d/0x2d0 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xf7/0x470 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f
The bug was triggered w/ below race condition:
fsync setattr ioctl - f2fs_do_sync_file - file_write_and_wait_range - f2fs_write_cache_pages : inode is non-compressed : cc.cluster_size = F2FS_I(inode)->i_cluster_size = 0 - tag_pages_for_writeback - f2fs_setattr - truncate_setsize - f2fs_truncate - f2fs_fileattr_set - f2fs_setflags_common - set_compress_context : F2FS_I(inode)->i_cluster_size = 4 : set_inode_flag(inode, FI_COMPRESSED_FILE) - f2fs_compressed_file : return true - f2fs_all_cluster_page_ready : "pgidx % cc->cluster_size" trigger dividing 0 issue
Let's change as below to fix this issue: - introduce a new atomic type variable .writeback in structure f2fs_inode_info to track the number of threads which calling f2fs_write_cache_pages(). - use .i_sem lock to protect .writeback update. - check .writeback before update compression context in f2fs_setflags_common() to avoid race w/ ->writepages.
Which versions are affected by CVE-2025-68772?
How do I fix CVE-2025-68772?
Apply the vendor's patch.
Is CVE-2025-68772 being exploited?
There is no known exploitation of CVE-2025-68772 in the wild and no public exploit code.
Sources
Also known as AZL-74387, BELL-CVE-2025-68772, DEBIAN-CVE-2025-68772, GHSA-p385-jwg8-m683, ROOT-OS-DEBIAN-11-CVE-2025-68772, ROOT-OS-DEBIAN-12-CVE-2025-68772 and 4 more.