ksmbd: remove stale channels from all sessions on teardown

Overview

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

ksmbd: remove stale channels from all sessions on teardown

ksmbd_sessions_deregister() removes a connection's channels from other sessions' channel lists only while conn->binding is still set:

if (conn->binding) {
	hash_for_each_safe(sessions_table, ...)
		ksmbd_chann_del(conn, sess);
}

conn->binding is a transient flag: it is cleared once a binding SESSION_SETUP completes, and also by a subsequent non-binding SESSION_SETUP on the same connection (a reauthentication on a bound channel, or a new SessionId==0 setup). A connection that has bound a channel into another session's ksmbd_chann_list and then clears conn->binding leaves that channel behind when it disconnects: the channel, whose chann->conn points at the now freed struct ksmbd_conn, stays on the owner session's list.

When the owning connection later tears down, the second loop dereferences the stale channel:

xa_for_each(&sess->ksmbd_chann_list, chann_id, chann)
	if (chann->conn != conn)
		ksmbd_conn_set_exiting(chann->conn);   /* freed */

which is a use-after-free write into the freed ksmbd_conn (the same stale channel is also walked by show_proc_session() through /proc). The session is leaked as well, because its channel list never empties.

Remove the conn->binding gate so a connection always removes its channels from every session on teardown.

Affected

• Linux >= b1b6ed903a6e2b3505a48706bcd499b447ef9e44 < f8200bb4994e65a2e5c5b314789eeae39078619d
• Linux >= 47b018dba6ec7ebf403fd2d1e713bc7acc9bbb23 < 9cd6d714d3ca0cff296542dc989696884e41970f
• Linux >= 9ef4dfd5edbd02f4bf10cd420a30896093d98a67 < b145f9b56c87f9c23ad5464ab0844dbc1de12b36
• Linux >= 5a5b0b7a01fe19b383b3c046546b5ae30c1a7d71 < a15cae16f4432a5ad919ee633e31b07178492955
• Linux >= faf8578c77f3d846aca9cd882c293e03eafcc6df < b10665730fbf6b5e45fe422badcbbc3f0df96ef5
• Linux e632f21a8bc0c59abc4960482836ac3782db93c0
• Linux >= 5.15.222 < 5.16
• Linux

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.