3.5 KiB
CVE-2025-22077
Description
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 afterrmmod") is intended to fix a null-ptr-deref in LOCKDEP, which ismentioned 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 realissue by reviving the kernel TCP socket.When a reconnect happens for a CIFS connection, the socket statetransitions 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_1forever, 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 abortsthe 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 onour side in that case, meaning we must not use a kernel socket forTCP whose sk->sk_net_refcnt is 0.The kernel socket does not have a reference to its netns to make itpossible to tear down netns without cleaning up every resource in it.For example, tunnel devices use a UDP socket internally, but we candestroy netns without removing such devices and let it completeduring exit. Otherwise, netns would be leaked when the last applicationdied.However, this is problematic for TCP sockets because TCP has timers toclose the connection gracefully even after the socket is close()d. Thelifetime of the socket and its netns is different from the lifetime ofthe underlying connection.If the socket user does not maintain the netns lifetime, the timer couldbe fired after the socket is close()d and its netns is freed up, resultingin use-after-free.Actually, we have seen so many similar issues and converted such socketsto have a reference to netns.That's why I converted the CIFS client socket to have a reference tonetns (sk->sk_net_refcnt == 1), which is somehow mentioned as out-of-scopeof CIFS and technically wrong in e9f2517a3e18, but is in-scope and rightfix.Regarding the LOCKDEP issue, we can prevent the module unload bybumping the module refcount when switching the LOCKDDEP key insock_lock_init_class_and_name(). [2]For a while, let's revert the bogus fix.Note that now we can use sk_net_refcnt_upgrade() for the socketconversion, but I'll do so later separately to make backport easy.
POC
Reference
No PoCs from references.