Linux Kernel CVE-2025-40105

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.

The affected component is the Linux kernel VFS/exportfs subsystem. No CPE strings or explicit version ranges were provided in the input, and the input CWE is N/A; the eight git.kernel.org stable commit references (e.g., 20863bb7fbb0, 56094ad3eaa2, 620f3b0ede9c, 7e0c8aaf4e28, 8004d4b8cbf1, b5abafd0aa8d, cebfbf40056a, eadc49999fa9) indicate the fix was backported across multiple stable branches, so all maintained kernel lines carrying commit f1ee616214cb up to those fixes are affected. Siemens has also published a downstream advisory at https://cert-portal.siemens.com/productcert/html/ssa-019113.html for its Linux-based products. Exact affected version boundaries should be confirmed against each distribution's kernel changelog since the NVD entries carry no version metadata here.