CVE-2025-71183 in Linux
Summary
by MITRE • 01/31/2026
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---
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Analysis
by VulDB Data Team • 03/26/2026
The vulnerability described in CVE-2025-71183 affects the btrfs filesystem implementation within the Linux kernel, specifically concerning the handling of inode references during logging operations. This issue arises from a flaw in the transaction logging mechanism that occurs when performing rename operations involving directories that contain subvolumes. The vulnerability manifests when conflicting inodes are not properly detected during log tree creation, leading to potential mount failures and system crashes. The core technical problem lies in the failure to correctly track inode reference conflicts during rename exchange operations, particularly when dealing with directories containing subvolumes. When a power failure occurs during such operations, the log replay process attempts to delete inodes that should not have been deleted, resulting in critical errors that prevent the filesystem from mounting properly.
The flaw occurs during the sequence of operations involving inode renaming and logging where the system fails to properly update transaction tracking for directory inodes during rename exchanges. Specifically, when two directories are exchanged through a rename operation, the system does not update the last_unlink_trans field for directory inodes, which creates a discrepancy in the logging mechanism. This leads to situations where inodes that should not be deleted are attempted for deletion during log replay, particularly when dealing with directories containing subvolumes. The issue is exacerbated by the fact that the log replay code is not prepared to handle directory entries that point to root items rather than standard inode items, which is a common scenario when subvolumes are present within directories. This problem falls under the category of improper handling of filesystem metadata during transactional operations, which is a well-documented weakness in filesystem implementations.
The operational impact of this vulnerability is severe, as it can lead to complete filesystem unmountability and system crashes when the btrfs filesystem attempts to replay corrupted transaction logs. The vulnerability specifically affects systems using btrfs filesystems that have undergone rename operations involving directories with subvolumes, making it particularly dangerous for production environments where data integrity is paramount. When the system attempts to delete a directory that contains a subvolume during log replay, it encounters an error because the replay_dir_deletes() and btrfs_unlink_inode() functions are not designed to handle directory entries pointing to root items. This results in a transaction abort and system panic, as evidenced by the stack trace showing the __btrfs_unlink_inode function failing at line 4345. The vulnerability demonstrates a clear failure in the filesystem's ability to maintain consistency during power failure scenarios, which is a fundamental requirement for any robust storage system.
Mitigation strategies for this vulnerability should focus on ensuring proper inode reference conflict detection during logging operations, particularly for directory inodes involved in rename exchanges. The fix requires modifications to the btrfs logging code to ensure that all inodes are properly checked for conflicts during log tree creation, regardless of their type or transaction state. System administrators should implement immediate updates to kernel versions containing the patched btrfs implementation, as this vulnerability can lead to complete data loss scenarios during power failures. Additionally, monitoring systems should be enhanced to detect filesystem inconsistencies that may indicate the presence of this vulnerability. Organizations using btrfs filesystems should also consider implementing regular filesystem checks and backup strategies to minimize the impact of potential failures. The vulnerability aligns with CWE-129, which addresses improper validation of array indices, and can be mapped to ATT&CK technique T1485 related to data destruction, as the vulnerability can result in filesystem corruption that renders data inaccessible. Proper kernel patching and system hardening measures are essential to prevent exploitation of this vulnerability, particularly in mission-critical environments where filesystem reliability is essential.