CVE-2026-89635

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

ksmbd: only rebind the reopened file's own oplock on durable reconnect

ksmbd reopen durable fd() walks the inode's m op list and rebinds every detached oplock to the reconnecting session:

list for each entry rcu(op, &ci->m op list, op entry,
			lockdep is held(&ci->m lock)) {
	if (op->conn)
		continue;
	op->conn = ksmbd conn get(fp->conn);
	op->sess = work->sess;
}

The only key is op->conn == NULL, which every detached durable handle on that inode matches, not just the one owned by fp. When two sessions hold durable handles on the same file and both disconnect, reconnecting one of them adopts the other session's oplock: op->sess is overwritten with the reconnecting session without taking a reference on it, while op->conn pins the connection.

The sibling teardown path, session fd check(), keys on the identity of the connection being torn down (op->conn == conn) rather than on shared state, and so does not have this problem.

Once the adopting session is destroyed, ksmbd session destroy() frees it while the foreign oplock still points at it. The reader in ksmbd close fd app instance id() validates only opinfo->conn, which is still live thanks to the reference taken above, and then dereferences the stale session:

if (!opinfo->conn) {
	up read(&fp->f ci->m lock);
	goto out;
}

ft = &opinfo->sess->file table;
write lock(&ft->lock);

BUG: KASAN: slab-use-after-free in raw write lock+0x74/0xd0 Write of size 4 at addr ffff88810a970528 by task kworker/0:0/9 Workqueue: ksmbd-io handle ksmbd work Call Trace: raw write lock+0x74/0xd0 ksmbd close fd app instance id+0x183/0x410 smb2 open+0x1346/0x4430 handle ksmbd work+0x2bb/0x7b0

Reached from an authenticated session against a share with the default durable-handle and oplock configuration: two sessions open the same file with a durable-v2 handle and an RH lease under distinct AppInstanceIds, both log off, one reconnects with DH2C, and a later durable-v2 create carrying the other AppInstanceId walks into the freed session.

Constrain the loop to the oplock owned by the file being reopened.