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CVE-2025-68772: f2fs: fix to avoid updating compression context during writeback

In the Linux kernel, the following vulnerability has been resolved: f2fs: fix to avoid updating compression context during writeback Bai, Shuangpeng <sjb7183@psu.edu> 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.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2025-68772 is a Linux kernel f2fs filesystem race that can trigger a divide-by-zero kernel Oops during file writeback. Business impact is mainly availability risk on systems using writable f2fs. The provided sources do not report active exploitation, CVSS, or remote attack details.

Executive priority

Treat as a focused availability issue, not an internet-wide emergency based on provided evidence. Patch through normal kernel update channels, with faster handling for systems using writable f2fs in multi-tenant or untrusted workload environments.

Technical view

The bug occurs when f2fs_write_cache_pages snapshots a zero compression cluster size while concurrent setattr/ioctl activity enables compression and updates inode compression context. f2fs_all_cluster_page_ready later evaluates page index modulo that zero cluster size, causing a divide error. Kernel stable fixes add writeback tracking and block compression-context updates during writeback.

Likely exposure

Exposure is most likely on Linux systems that mount f2fs and permit local workloads to write files and change f2fs compression attributes. The bundle lists Linux as affected, but distribution package status is not provided.

Exploitation context

The evidence shows a syzkaller-style local race involving fsync, setattr/truncate, and ioctl file-attribute changes. CISA KEV status is false in the bundle, and no cited source claims active exploitation.

Researcher notes

The source describes a race between writeback and compression flag/context updates. Key validation should confirm whether a kernel contains the f2fs_inode_info writeback counter and f2fs_setflags_common guard. No exploit code, PoC reliability, privileges, or distro-specific fixed package versions are provided.

Mitigation direction

  • Update affected Linux kernels to versions containing the referenced stable fixes.
  • Check your Linux distribution advisories for packaged kernel availability and backport status.
  • Prioritize writable f2fs hosts with untrusted local users, containers, or mobile/embedded workloads.
  • If patching is delayed, reduce unnecessary f2fs write access where operationally feasible.

Validation and detection

  • Inventory hosts using f2fs mounts and record running kernel versions.
  • Compare deployed kernels against distribution advisories and the referenced stable commits.
  • Review kernel logs for f2fs-related divide errors or Oops events.
  • Confirm patched kernels include the writeback tracking fix for f2fs compression context updates.
Prepared
Confidence
medium
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
6Source links

Vulnerability timeline

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  2. CVE publishedCVE Program

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  3. CVE updatedCVE Program

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Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux4c8ff7095bef64fc47e996a938f7d57f9e077da3, 4c8ff7095bef64fc47e996a938f7d57f9e077da3, 4c8ff7095bef64fc47e996a938f7d57f9e077da3, 4c8ff7095bef64fc47e996a938f7d57f9e077da3, 4c8ff7095bef64fc47e996a938f7d57f9e077da3unaffected
LinuxLinux5.6, 0, 6.1.160, 6.6.120, 6.12.64, 6.18.3, 6.19affected
Weakness

CWE details

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