Affected: Linux

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

Revert "smb: client: fix TCP timers deadlock after rmmod"

This reverts commit e9f2517a3e18a54a3943c098d2226b245d488801.

Commit e9f2517a3e18 ("smb: client: fix TCP timers deadlock after rmmod") is intended to fix a null-ptr-deref in LOCKDEP, which is mentioned as CVE-2024-54680, but is actually did not fix anything; The issue can be reproduced on top of it. [0]

Also, it reverted the change by commit ef7134c7fc48 ("smb: client: Fix use-after-free of network namespace.") and introduced a real issue by reviving the kernel TCP socket.

When a reconnect happens for a CIFS connection, the socket state transitions to FIN_WAIT_1. Then, inet_csk_clear_xmit_timers_sync() in tcp_close() stops all timers for the socket.

If an incoming FIN packet is lost, the socket will stay at FIN_WAIT_1 forever, and such sockets could be leaked up to net.ipv4.tcp_max_orphans.

Usually, FIN can be retransmitted by the peer, but if the peer aborts the connection, the issue comes into reality.

I warned about this privately by pointing out the exact report [1], but the bogus fix was finally merged.

So, we should not stop the timers to finally kill the connection on our side in that case, meaning we must not use a kernel socket for TCP whose sk->sk_net_refcnt is 0.

The kernel socket does not have a reference to its netns to make it possible to tear down netns without cleaning up every resource in it.

For example, tunnel devices us…