Cloudanix VulnDB

CVE-2025-40303

None

CVSS

—

EPSS

0.1%

Published

Dec 8, 2025

CISA due date

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Cloudanix analysis

Schedule a fix SSVC: Track

A bug in Linux file system code could cause crashes when errors happen on certain storage setups, requiring updates to prevent problems during shutdown.

Exploitation
Local Privilege
Attacker needs
Local User
Complexity
Moderate
Impact
Denial Of Service
Component
OS kernel
Class
Use After Free
Remediation
Upgrade
Effort
Medium
Patch risk
Low

What it actually does

Use-after-free in btrfs writeback path when an errored filesystem with RAID56 metadata attempts to flush dirty tree blocks after workqueues are stopped during unmount.

Why it matters to the business

Kernel crashes or memory corruption on systems using btrfs with RAID5/6 metadata under error conditions, potentially leading to data unavailability and forced reboots; affects many older Ubuntu LTS releases with no active exploitation reported.

How an attack unfolds

An attacker with local access triggers a btrfs transaction abort (via extent tree corruption or similar), leaving dirty metadata in the page cache. On unmount, iput on the btree inode initiates writeback after workers are stopped, queuing work into freed rmw_workers and causing UAF.

How to fix it

Upgrade to fixed kernel versions: linux 3.11.0-12.19 (14.04), 4.2.0-16.19 (16.04), 4.13.0-16.19 (18.04) and equivalents for all listed subpackages; or apply commit 066ee13f05fbd82ada01883e51f0695172f98dff in stable trees.

How to confirm the fix worked

Confirm kernel version matches or exceeds the listed fixed releases for the affected package; verify btrfs error handling path contains the early failure return in write_one_eb() for errored filesystems.

Typical attack path

  1. Gain local access to a system using btrfs RAID56 metadata
  2. Trigger filesystem error state via crafted corruption or workload
  3. Perform unmount or shutdown sequence
  4. Observe use-after-free during attempted metadata writeback into stopped workqueues

How to detect it

Review kernel logs for warnings from queue_work on stopped rmw_workers, use-after-free reports involving btrfs or btree inode during close_ctree, and any btrfs transaction abort events preceding unmounts.

What your security team should do

  • Prioritize patching any remaining systems still on the listed vulnerable Ubuntu kernels
  • Monitor btrfs error logs and avoid workloads that can trigger transaction aborts on RAID56 metadata volumes
  • Test upgraded kernels in staging environments before broad deployment

The record

In the Linux kernel, the following vulnerability has been resolved: btrfs: ensure no dirty metadata is written back for an fs with errors [BUG] During development of a minor feature (make sure all btrfs_bio::end_io() is called in task context), I noticed a crash in generic/388, where metadata writes triggered new works after btrfs_stop_all_workers(). It turns out that it can even happen without any code modification, just using RAID5 for metadata and the same workload from generic/388 is going to trigger the use-after-free. [CAUSE] If btrfs hits an error, the fs is marked as error, no new transaction is allowed thus metadata is in a frozen state. But there are some metadata modifications before that error, and they are still in the btree inode page cache. Since there will be no real transaction commit, all those dirty folios are just kept as is in the page cache, and they can not be invalidated by invalidate_inode_pages2() call inside close_ctree(), because they are dirty. And finally after btrfs_stop_all_workers(), we call iput() on btree inode, which triggers writeback of those dirty metadata. And if the fs is using RAID56 metadata, this will trigger RMW and queue new works into rmw_workers, which is already stopped, causing warning from queue_work() and use-after-free. [FIX] Add a special handling for write_one_eb(), that if the fs is already in an error state, immediately mark the bbio as failure, instead of really submitting them. Then during close_ctree(), iput() will just discard all those dirty tree blocks without really writing them back, thus no more new jobs for already stopped-and-freed workqueues. The extra discard in write_one_eb() also acts as an extra safenet. E.g. the transaction abort is triggered by some extent/free space tree corruptions, and since extent/free space tree is already corrupted some tree blocks may be allocated where they shouldn't be (overwriting existing tree blocks). In that case writing them back will further corrupting the fs.

Affected packages

Ecosystem Package Introduced Fixed
Linux Kernel 0 6.6.117
Linux Kernel 3.10.0 6.6.117
Mageia:9 kernel 0 6.6.120-1.mga9
Mageia:9 kernel-linus 0 6.6.120-1.mga9
Mageia:9 kmod-virtualbox 0 7.1.14-14.mga9
Mageia:9 kmod-xtables-addons 0 3.24-88.mga9
openSUSE:Leap 16.0 dtb-aarch64 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-64kb 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-azure 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-default 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-default-base 0 6.12.0-160000.9.1.160000.2.6
openSUSE:Leap 16.0 kernel-docs 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-kvmsmall 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-obs-build 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-obs-qa 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-rt 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-source 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-syms 0 6.12.0-160000.9.1
openSUSE:Leap 16.0 kernel-zfcpdump 0 6.12.0-160000.9.1

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