CVE-2025-71183

Medium · 5.5

CVSS

5.5

EPSS

0.3%

Published

Jan 31, 2026

CISA due date

—

Cloudanix analysis

Schedule a fix SSVC: Track

A flaw in Linux file-system logging can prevent a computer from starting up correctly after an unexpected shutdown if certain file-renaming steps occurred beforehand.

Exploitation: Local Privilege
Attacker needs: Low Privilege
Complexity: Low
Impact: Denial Of Service
Component: OS kernel
Class: Race Condition
Remediation: Upgrade
Effort: Medium
Patch risk: Low

What it actually does

Race condition in Btrfs log replay after rename-exchange of directories allows log tree to omit one inode, causing incorrect deletion attempt of a directory containing a subvolume during replay; replay_dir_deletes and btrfs_unlink_inode lack handling for directory entries pointing to root items, aborting the transaction with error -2.

Why it matters to the business

Local users or automated workloads performing rename and fsync sequences can trigger unmountable filesystems after power loss, leading to extended downtime, forced recovery from backups, and operational disruption on systems using Btrfs; widespread kernel deployments increase exposure across servers and containers.

How an attack unfolds

An attacker with local access performs cross-directory renames or rename-exchange operations between directories (one containing a subvolume), updates a child file's last_unlink_trans via rename, then triggers an fsync on that file. After a subsequent power failure the incomplete log tree causes replay to attempt deletion of the wrong directory inode, failing when a subvolume root is referenced and aborting the mount.

How to fix it

Upgrade affected Linux kernels to the fixed commit c7f0207db68d5a1b4af23acbef1a8e8ddc431ebb or later stable releases containing the btrfs inode logging change; for MinimOS packages update loki-fips-2.9 and related components to 2.9.17-r1 or newer. Reboot after kernel update and verify Btrfs mounts succeed on systems with prior rename activity.

How to confirm the fix worked

Confirm kernel version contains commit c7f0207db68d5a1b4af23acbef1a8e8ddc431ebb, run btrfs filesystem check on test volumes after simulated rename-exchange plus fsync plus power-loss scenarios, and verify no 'failed to delete reference to subvol' or 'Transaction aborted (error -2)' messages appear during mount.

Typical attack path

Obtain local shell or process execution on a Btrfs filesystem
Create or locate directories with subvolumes and perform rename-exchange or multi-step renames
Trigger fsync on a file whose parent was involved in the rename
Induce or wait for power failure or unclean shutdown
Observe failed mount with transaction abort during log replay

How to detect it

Search system logs and kernel ring buffer for Btrfs mount failures during tree-log replay; inspect dmesg, journalctl, and /var/log/messages for critical messages referencing failed subvol reference deletion or transaction abort with error -2 after power-loss events.

BTRFS critical (device
failed to delete reference to subvol, root
BTRFS: Transaction aborted (error -2)
__btrfs_unlink_inode+0x416/0x440

What your security team should do

Prioritize kernel upgrades on all Btrfs hosts within 30 days given local attack surface
Add Btrfs log-replay failure patterns to monitoring for rapid detection of affected systems
Restrict unprivileged local access where feasible until patches are deployed
Test fsync-heavy workloads and rename patterns in staging before production rollout

The record

In the Linux kernel, the following vulnerability has been resolved: btrfs: always detect conflicting inodes when logging inode refs After rename exchanging (either with the rename exchange operation or regular renames in multiple non-atomic steps) two inodes and at least one of them is a directory, we can end up with a log tree that contains only of the inodes and after a power failure that can result in an attempt to delete the other inode when it should not because it was not deleted before the power failure. In some case that delete attempt fails when the target inode is a directory that contains a subvolume inside it, since the log replay code is not prepared to deal with directory entries that point to root items (only inode items). 1) We have directories "dir1" (inode A) and "dir2" (inode B) under the same parent directory; 2) We have a file (inode C) under directory "dir1" (inode A); 3) We have a subvolume inside directory "dir2" (inode B); 4) All these inodes were persisted in a past transaction and we are currently at transaction N; 5) We rename the file (inode C), so at btrfs_log_new_name() we update inode C's last_unlink_trans to N; 6) We get a rename exchange for "dir1" (inode A) and "dir2" (inode B), so after the exchange "dir1" is inode B and "dir2" is inode A. During the rename exchange we call btrfs_log_new_name() for inodes A and B, but because they are directories, we don't update their last_unlink_trans to N; 7) An fsync against the file (inode C) is done, and because its inode has a last_unlink_trans with a value of N we log its parent directory (inode A) (through btrfs_log_all_parents(), called from btrfs_log_inode_parent()). 8) So we end up with inode B not logged, which now has the old name of inode A. At copy_inode_items_to_log(), when logging inode A, we did not check if we had any conflicting inode to log because inode A has a generation lower than the current transaction (created in a past transaction); 9) After a power failure, when replaying the log tree, since we find that inode A has a new name that conflicts with the name of inode B in the fs tree, we attempt to delete inode B... this is wrong since that directory was never deleted before the power failure, and because there is a subvolume inside that directory, attempting to delete it will fail since replay_dir_deletes() and btrfs_unlink_inode() are not prepared to deal with dir items that point to roots instead of inodes. When that happens the mount fails and we get a stack trace like the following: [87.2314] BTRFS info (device dm-0): start tree-log replay [87.2318] BTRFS critical (device dm-0): failed to delete reference to subvol, root 5 inode 256 parent 259 [87.2332] ------------[ cut here ]------------ [87.2338] BTRFS: Transaction aborted (error -2) [87.2346] WARNING: CPU: 1 PID: 638968 at fs/btrfs/inode.c:4345 __btrfs_unlink_inode+0x416/0x440 [btrfs] [87.2368] Modules linked in: btrfs loop dm_thin_pool (...) [87.2470] CPU: 1 UID: 0 PID: 638968 Comm: mount Tainted: G W 6.18.0-rc7-btrfs-next-218+ #2 PREEMPT(full) [87.2489] Tainted: [W]=WARN [87.2494] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014 [87.2514] RIP: 0010:__btrfs_unlink_inode+0x416/0x440 [btrfs] [87.2538] Code: c0 89 04 24 (...) [87.2568] RSP: 0018:ffffc0e741f4b9b8 EFLAGS: 00010286 [87.2574] RAX: 0000000000000000 RBX: ffff9d3ec8a6cf60 RCX: 0000000000000000 [87.2582] RDX: 0000000000000002 RSI: ffffffff84ab45a1 RDI: 00000000ffffffff [87.2591] RBP: ffff9d3ec8a6ef20 R08: 0000000000000000 R09: ffffc0e741f4b840 [87.2599] R10: ffff9d45dc1fffa8 R11: 0000000000000003 R12: ffff9d3ee26d77e0 [87.2608] R13: ffffc0e741f4ba98 R14: ffff9d4458040800 R15: ffff9d44b6b7ca10 [87.2618] FS: 00007f7b9603a840(0000) GS:ffff9d4658982000(0000) knlGS:0000000000000000 [87. ---truncated---

Affected packages

Ecosystem	Package	Introduced	Fixed
Linux	Kernel	4.6.0	6.1.161
openSUSE:Leap 16.0	dtb-aarch64	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-64kb	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-azure	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-default	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-default-base	0	6.12.0-160000.27.1.160000.2.8
openSUSE:Leap 16.0	kernel-docs	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-kvmsmall	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-obs-build	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-obs-qa	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-rt	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-source	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-syms	0	6.12.0-160000.27.1
openSUSE:Leap 16.0	kernel-zfcpdump	0	6.12.0-160000.27.1