Linux Kernel up to 6.16-rc3 btrfs btrfs_unlink last_unlink_trans race condition

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Summaryinfo

A vulnerability was found in Linux Kernel up to 6.1.142/6.6.95/6.12.35/6.15.4/6.16-rc3. It has been rated as critical. Affected by this vulnerability is the function btrfs_unlink of the component btrfs. Performing a manipulation of the argument last_unlink_trans results in race condition. This vulnerability is known as CVE-2025-38365. No exploit is available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.1.142/6.6.95/6.12.35/6.15.4/6.16-rc3. It has been classified as critical. This affects the function btrfs_unlink of the component btrfs. The manipulation of the argument last_unlink_trans with an unknown input leads to a race condition vulnerability. CWE is classifying the issue as CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. The impact remains unknown. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix a race between renames and directory logging We have a race between a rename and directory inode logging that if it happens and we crash/power fail before the rename completes, the next time the filesystem is mounted, the log replay code will end up deleting the file that was being renamed. This is best explained following a step by step analysis of an interleaving of steps that lead into this situation. Consider the initial conditions: 1) We are at transaction N; 2) We have directories A and B created in a past transaction (< N); 3) We have inode X corresponding to a file that has 2 hardlinks, one in directory A and the other in directory B, so we'll name them as "A/foo_link1" and "B/foo_link2". Both hard links were persisted in a past transaction (< N); 4) We have inode Y corresponding to a file that as a single hard link and is located in directory A, we'll name it as "A/bar". This file was also persisted in a past transaction (< N). The steps leading to a file loss are the following and for all of them we are under transaction N: 1) Link "A/foo_link1" is removed, so inode's X last_unlink_trans field is updated to N, through btrfs_unlink() -> btrfs_record_unlink_dir(); 2) Task A starts a rename for inode Y, with the goal of renaming from "A/bar" to "A/baz", so we enter btrfs_rename(); 3) Task A inserts the new BTRFS_INODE_REF_KEY for inode Y by calling btrfs_insert_inode_ref(); 4) Because the rename happens in the same directory, we don't set the last_unlink_trans field of directoty A's inode to the current transaction id, that is, we don't cal btrfs_record_unlink_dir(); 5) Task A then removes the entries from directory A (BTRFS_DIR_ITEM_KEY and BTRFS_DIR_INDEX_KEY items) when calling __btrfs_unlink_inode() (actually the dir index item is added as a delayed item, but the effect is the same); 6) Now before task A adds the new entry "A/baz" to directory A by calling btrfs_add_link(), another task, task B is logging inode X; 7) Task B starts a fsync of inode X and after logging inode X, at btrfs_log_inode_parent() it calls btrfs_log_all_parents(), since inode X has a last_unlink_trans value of N, set at in step 1; 8) At btrfs_log_all_parents() we search for all parent directories of inode X using the commit root, so we find directories A and B and log them. Bu when logging direct A, we don't have a dir index item for inode Y anymore, neither the old name "A/bar" nor for the new name "A/baz" since the rename has deleted the old name but has not yet inserted the new name - task A hasn't called yet btrfs_add_link() to do that. Note that logging directory A doesn't fallback to a transaction commit because its last_unlink_trans has a lower value than the current transaction's id (see step 4); 9) Task B finishes logging directories A and B and gets back to btrfs_sync_file() where it calls btrfs_sync_log() to persist the log tree; 10) Task B successfully persisted the log tree, btrfs_sync_log() completed with success, and a power failure happened. We have a log tree without any directory entry for inode Y, so the log replay code deletes the entry for inode Y, name "A/bar", from the subvolume tree since it doesn't exist in the log tree and the log tree is authorative for its index (we logged a BTRFS_DIR_LOG_INDEX_KEY item that covers the index range for the dentry that corresponds to "A/bar"). Since there's no other hard link for inode Y and the log replay code deletes the name "A/bar", the file is lost. The issue wouldn't happen if task B synced the log only after task A called btrfs_log_new_name(), which would update the log with the new name for inode Y ("A/bar"). Fix this by pinning the log root during renames before removing the old directory entry, and unpinning af ---truncated---

The advisory is shared at git.kernel.org. This vulnerability is uniquely identified as CVE-2025-38365 since 04/16/2025. The exploitability is told to be difficult. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 253428 (SUSE SLES15 Security Update : kernel (SUSE-SU-2025:02923-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.1.143, 6.6.96, 6.12.36, 6.15.5 or 6.16-rc4 eliminates this vulnerability. Applying the patch 51bd363c7010d033d3334daf457c824484bf9bf0/aeeae8feeaae4445a86f9815273e81f902dc1f5b/2088895d5903082bb9021770b919e733c57edbc1/8c6874646c21bd820cf475e2874e62c133954023/3ca864de852bc91007b32d2a0d48993724f4abad is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (253428) and CERT Bund (WID-SEC-2025-1653). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

  • Debian Linux
  • Amazon Linux 2
  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • IBM QRadar SIEM
  • SUSE openSUSE
  • RESF Rocky Linux
  • Dell Avamar
  • Open Source Linux Kernel
  • Dell NetWorker
  • Dell Secure Connect Gateway

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 4.6
VulDB Meta Temp Score: 4.6

VulDB Base Score: 4.6
VulDB Temp Score: 4.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 4.7
NVD Vector: 🔒

CVSSv2info

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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Race condition
CWE: CWE-362
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 253428
Nessus Name: SUSE SLES15 Security Update : kernel (SUSE-SU-2025:02923-1)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.1.143/6.6.96/6.12.36/6.15.5/6.16-rc4
Patch: 51bd363c7010d033d3334daf457c824484bf9bf0/aeeae8feeaae4445a86f9815273e81f902dc1f5b/2088895d5903082bb9021770b919e733c57edbc1/8c6874646c21bd820cf475e2874e62c133954023/3ca864de852bc91007b32d2a0d48993724f4abad

Timelineinfo

04/16/2025 CVE reserved
07/25/2025 +100 days Advisory disclosed
07/25/2025 +0 days VulDB entry created
12/23/2025 +151 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-38365 (🔒)
GCVE (CVE): GCVE-0-2025-38365
GCVE (VulDB): GCVE-100-317625
CERT Bund: WID-SEC-2025-1653 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 07/25/2025 15:34
Updated: 12/23/2025 11:46
Changes: 07/25/2025 15:34 (60), 08/18/2025 01:57 (7), 08/19/2025 17:29 (1), 08/24/2025 01:47 (2), 09/14/2025 14:20 (1), 09/15/2025 15:45 (1), 09/28/2025 12:22 (1), 11/02/2025 05:57 (1), 11/16/2025 23:13 (1), 12/16/2025 22:50 (11), 12/23/2025 11:46 (1)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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