CVE-2025-68775

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

net/handshake: duplicate handshake cancellations leak socket

When a handshake request is cancelled it is removed from the

handshake_net->hn_requests list, but it is still present in the

handshake_rhashtbl until it is destroyed.

If a second cancellation request arrives for the same handshake request,

then remove_pending() will return false... and assuming

HANDSHAKE_F_REQ_COMPLETED isn't set in req->hr_flags, we'll continue

processing through the out_true label, where we put another reference on

the sock and a refcount underflow occurs.

This can happen for example if a handshake times out - particularly if

the SUNRPC client sends the AUTH_TLS probe to the server but doesn't

follow it up with the ClientHello due to a problem with tlshd. When the

timeout is hit on the server, the server will send a FIN, which triggers

a cancellation request via xs_reset_transport(). When the timeout is

hit on the client, another cancellation request happens via

xs_tls_handshake_sync().

Add a test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) in the pending cancel

path so duplicate cancels can be detected.