Description

In the Linux kernel, the following vulnerability has been resolved:

fix a couple of races in MNT_TREE_BENEATH handling by do_move_mount()

Normally do_lock_mount(path, _) is locking a mountpoint pinned by
*path and at the time when matching unlock_mount() unlocks that
location it is still pinned by the same thing.

Unfortunately, for 'beneath' case it's no longer that simple -
the object being locked is not the one *path points to. It's the
mountpoint of path->mnt. The thing is, without sufficient locking
->mnt_parent may change under us and none of the locks are held
at that point. The rules are
* mount_lock stabilizes m->mnt_parent for any mount m.
* namespace_sem stabilizes m->mnt_parent, provided that
m is mounted.
* if either of the above holds and refcount of m is positive,
we are guaranteed the same for refcount of m->mnt_parent.

namespace_sem nests inside inode_lock(), so do_lock_mount() has
to take inode_lock() before grabbing namespace_sem. It does
recheck that path->mnt is still mounted in the same place after
getting namespace_sem, and it does take care to pin the dentry.
It is needed, since otherwise we might end up with racing mount --move
(or umount) happening while we were getting locks; in that case
dentry would no longer be a mountpoint and could've been evicted
on memory pressure along with its inode - not something you want
when grabbing lock on that inode.

However, pinning a dentry is not enough - the matching mount is
also pinned only by the...

Classification

CVE ID: CVE-2025-37988

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.02% (probability of being exploited)

EPSS Percentile: 4.6% (scored less or equal to compared to others)

EPSS Date: 2025-06-18 (when was this score calculated)

References

https://nvd.nist.gov/vuln/detail/CVE-2025-37988
https://git.kernel.org/stable/c/4f435c1f4c48ff84968e2d9159f6fa41f46cf998
https://git.kernel.org/stable/c/a61afd54826ac24c2c93845c4f441dbc344875b1
https://git.kernel.org/stable/c/d4b21e8cd3d7efa2deb9cff534f0133e84f35086
https://git.kernel.org/stable/c/0d039eac6e5950f9d1ecc9e410c2fd1feaeab3b6

Timeline