Paolo points out that mptcp_disconnect is bogus: "lock_sock(sk); looks suspicious (lock should be already held by the caller) And call to: tcp_disconnect(sk, flags); too, sk is not a tcp socket".
->disconnect() gets called from e.g. inet_stream_connect when one tries to disassociate a connected socket again (to re-connect without closing the socket first). MPTCP however uses mptcp_stream_connect, not inet_stream_connect, for the mptcp-socket connect call. inet_stream_connect only gets called indirectly, for the tcp socket, so any ->disconnect() calls end up calling tcp_disconnect for that tcp subflow sk. This also explains why syzkaller has not yet reported a problem here. So for now replace this with a stub that doesn't do anything. Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/14 Acked-by: Paolo Abeni <pab...@redhat.com> Signed-off-by: Florian Westphal <f...@strlen.de> --- net/mptcp/protocol.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index b22a63ba2348..6e0188f5d3f3 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -1316,11 +1316,12 @@ static void mptcp_copy_inaddrs(struct sock *msk, const struct sock *ssk) static int mptcp_disconnect(struct sock *sk, int flags) { - lock_sock(sk); - __mptcp_clear_xmit(sk); - release_sock(sk); - mptcp_cancel_work(sk); - return tcp_disconnect(sk, flags); + /* Should never be called. + * inet_stream_connect() calls ->disconnect, but that + * refers to the subflow socket, not the mptcp one. + */ + WARN_ON_ONCE(1); + return 0; } #if IS_ENABLED(CONFIG_MPTCP_IPV6) -- 2.26.2
