CVE-2025-40105
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk5th percentile - higher than 5% of all known CVEs
Summary
A vulnerability in the Linux kernel causes a leak of disconnected dentries during filesystem unmount. When open_by_handle_at() creates a disconnected dentry and reconnection fails, flags become inconsistent, preventing immediate memory reclamation. This leads to a "Busy inodes after unmount" error and potential system instability.
Risk Assessment
The risk includes inability to unmount filesystems due to memory leaks, potentially causing system instability, data loss, or forced reboots. A local attacker with appropriate privileges could exploit this to cause a denial of service (DoS).
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit addressing the vulnerability). Monitor official security advisories from your distribution and apply the patch as soon as it becomes available.
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In the Linux kernel XFS filesystem, during AGI repair, the function xrep_iunlink_walk_ondisk_bucket may attempt to use the pointer sc->sa.agi_bp, which can be null if the buffer verifier fails. The fix uses ragi->agi_bp instead, which skips verifier checks, to avoid walking off the end of memory.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: vfs: Don't leak disconnected dentries on umount When user calls open_by_handle_at() on some inode that is not cached, we will create disconnected dentry for it. If such dentry is a directory, exportfs_decode_fh_raw() will then try to connect this dentry to the dentry tree through reconnect_path(). It may happen for various reasons (such as corrupted fs or race with rename) that the call to lookup_one_unlocked() in reconnect_one() will fail to find the dentry we are trying to reconnect and instead create a new dentry under the parent. Now this dentry will not be marked as disconnected although the parent still may well be disconnected (at least in case this inconsistency happened because the fs is corrupted and .. doesn't point to the real parent directory). This creates inconsistency in disconnected flags but AFAICS it was mostly harmless. At least until commit f1ee616214cb ("VFS: don't keep disconnected dentries on d_anon") which removed adding of most disconnected dentries to sb->s_anon list. Thus after this commit cleanup of disconnected dentries implicitely relies on the fact that dput() will immediately reclaim such dentries. However when some leaf dentry isn't marked as disconnected, as in the scenario described above, the reclaim doesn't happen and the dentries are "leaked". Memory reclaim can eventually reclaim them but otherwise they stay in memory and if umount comes first, we hit infamous "Busy inodes after unmount" bug. Make sure all dentries created under a disconnected parent are marked as disconnected as well.