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.

Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for handling handshake requests")
Suggested-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://patch.msgid.link/20251209193015.3032058-1-smayhew@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/handshake/request.c b/net/handshake/request.c
index 89435ed755cd0045605d104e71370e4211439ffb..6b7e3e0bf3996effe4af4419cbb6bd8cd0e7a8db 100644 (file)
--- a/net/handshake/request.c
+++ b/net/handshake/request.c
@@ -326,7 +326,11 @@ bool handshake_req_cancel(struct sock *sk)
 
        hn = handshake_pernet(net);
        if (hn && remove_pending(hn, req)) {
-               /* Request hadn't been accepted */
+               /* Request hadn't been accepted - mark cancelled */
+               if (test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED, &req->hr_flags)) {
+                       trace_handshake_cancel_busy(net, req, sk);
+                       return false;
+               }
                goto out_true;
        }
        if (test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED, &req->hr_flags)) {