mptcp: reset 'first' and ack_hint on subflow close

Just like with last_snd, we have to NULL 'first' on subflow close.

ack_hint isn't strictly required (its never dereferenced), but better to
clear this explicitly as well instead of making it an exception.

msk->first is dereferenced unconditionally at accept time, but
at that point the ssk is not on the conn_list yet -- this means
worker can't see it when iterating the conn_list.

Reported-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index a58da04..3dcb564 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2169,6 +2169,12 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
        if (ssk == msk->last_snd)
                msk->last_snd = NULL;
 
+       if (ssk == msk->ack_hint)
+               msk->ack_hint = NULL;
+
+       if (ssk == msk->first)
+               msk->first = NULL;
+
        if (msk->subflow && ssk == msk->subflow->sk)
                mptcp_dispose_initial_subflow(msk);
 }
@@ -3297,6 +3303,9 @@ static int mptcp_stream_accept(struct socket *sock, struct socket *newsock,
                /* PM/worker can now acquire the first subflow socket
                 * lock without racing with listener queue cleanup,
                 * we can notify it, if needed.
+                *
+                * Even if remote has reset the initial subflow by now
+                * the refcnt is still at least one.
                 */
                subflow = mptcp_subflow_ctx(msk->first);
                list_add(&subflow->node, &msk->conn_list);