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(). Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for handling handshake requests") Signed-off-by: Scott Mayhew --- net/handshake/request.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/handshake/request.c b/net/handshake/request.c index 274d2c89b6b2..c7b20d167a55 100644 --- a/net/handshake/request.c +++ b/net/handshake/request.c @@ -333,6 +333,10 @@ bool handshake_req_cancel(struct sock *sk) return false; } + /* Duplicate cancellation request */ + trace_handshake_cancel_none(net, req, sk); + return false; + out_true: trace_handshake_cancel(net, req, sk); -- 2.51.0