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Linux KernelOperating system · Linux

CVE-2025-39779

MEDIUM · 5.5 CVSS v3.1 Published 2025-09-11
Fix available
A fix is available. Upgrade to 6.12.44 / 6.16.4 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: btrfs: subpage: keep TOWRITE tag until folio is cleaned btrfs_subpage_set_writeback() calls folio_start_writeback() the first time a folio is written back, and it also clears the PAGECACHE_TAG_TOWRITE tag even if there are still dirty blocks in the folio. This can break ordering guarantees, such as those required by btrfs_wait_ordered_extents(). That ordering breakage leads to a real failure. For example, running generic/464 on a zoned setup will hit the following ASSERT. This happens because the broken ordering fails to flush existing dirty pages before the file size is truncated. assertion failed: !list_empty(&ordered->list) :: 0, in fs/btrfs/zoned.c:1899 ------------[ cut here ]------------ kernel BUG at fs/btrfs/zoned.c:1899! Oops: invalid opcode: 0000 [#1] SMP NOPTI CPU: 2 UID: 0 PID: 1906169 Comm: kworker/u130:2 Kdump: loaded Not tainted 6.16.0-rc6-BTRFS-ZNS+ #554 PREEMPT(voluntary) Hardware name: Supermicro Super Server/H12SSL-NT, BIOS 2.0 02/22/2021 Workqueue: btrfs-endio-write btrfs_work_helper [btrfs] RIP: 0010:btrfs_finish_ordered_zoned.cold+0x50/0x52 [btrfs] RSP: 0018:ffffc9002efdbd60 EFLAGS: 00010246 RAX: 000000000000004c RBX: ffff88811923c4e0 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffffffff827e38b1 RDI: 00000000ffffffff RBP: ffff88810005d000 R08: 00000000ffffdfff R09: ffffffff831051c8 R10: ffffffff83055220 R11: 0000000000000000 R12: ffff8881c2458c00 R13: ffff88811923c540 R14: ffff88811923c5e8 R15: ffff8881c1bd9680 FS: 0000000000000000(0000) GS:ffff88a04acd0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f907c7a918c CR3: 0000000004024000 CR4: 0000000000350ef0 Call Trace: <TASK> ? srso_return_thunk+0x5/0x5f btrfs_finish_ordered_io+0x4a/0x60 [btrfs] btrfs_work_helper+0xf9/0x490 [btrfs] process_one_work+0x204/0x590 ? srso_return_thunk+0x5/0x5f worker_thread+0x1d6/0x3d0 ? __pfx_worker_thread+0x10/0x10 kthread+0x118/0x230 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x205/0x260 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> Consider process A calling writepages() with WB_SYNC_NONE. In zoned mode or for compressed writes, it locks several folios for delalloc and starts writing them out. Let's call the last locked folio folio X. Suppose the write range only partially covers folio X, leaving some pages dirty. Process A calls btrfs_subpage_set_writeback() when building a bio. This function call clears the TOWRITE tag of folio X, whose size = 8K and the block size = 4K. It is following state. 0 4K 8K |/////|/////| (flag: DIRTY, tag: DIRTY) <-----> Process A will write this range. Now suppose process B concurrently calls writepages() with WB_SYNC_ALL. It calls tag_pages_for_writeback() to tag dirty folios with PAGECACHE_TAG_TOWRITE. Since folio X is still dirty, it gets tagged. Then, B collects tagged folios using filemap_get_folios_tag() and must wait for folio X to be written before returning from writepages(). 0 4K 8K |/////|/////| (flag: DIRTY, tag: DIRTY|TOWRITE) However, between tagging and collecting, process A may call btrfs_subpage_set_writeback() and clear folio X's TOWRITE tag. 0 4K 8K | |/////| (flag: DIRTY|WRITEBACK, tag: DIRTY) As a result, process B won't see folio X in its batch, and returns without waiting for it. This breaks the WB_SYNC_ALL ordering requirement. Fix this by using btrfs_subpage_set_writeback_keepwrite(), which retains the TOWRITE tag. We now manually clear the tag only after the folio becomes clean, via the xas operation.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis

A detailed technical summary for this CVE is being prepared.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 5.13, < 6.12.44>= 6.13, < 6.16.4= 6.17

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 6.12.44 / 6.16.4 or later
Fixed in 6.12.446.16.4
Vendor patch git.kernel.org →
Recommended fix High confidence

Linux Kernel 6.12.44+ (for 6.12.x), 6.16.4+ (for 6.13-6.16.x), or 6.18+ (for 6.17)

  1. Identify the current Linux kernel version running on affected systems using `uname -r`
  2. Determine which branch of the kernel is in use (e.g., 6.12.y, 6.13.y, 6.17.x)
  3. Upgrade the kernel to a fixed version: for 6.12.x line upgrade to >= 6.12.44, for 6.13-6.16.x upgrade to >= 6.16.4, for 6.17 upgrade to 6.18 or later
  4. Update bootloader configuration if necessary (e.g., update GRUB for Debian/Ubuntu, or boot config for RHEL/CentOS)
  5. Reboot the system into the new kernel using `reboot` or equivalent
  6. Verify the new kernel is running with `uname -r` and confirm the version contains the fix
Caveat Kernel upgrades typically require system reboot and may require driver/compatibility verification; ensure critical BTRFS workloads are backed up before upgrade

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

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