inet_connection_sock: clear inet_num out of destroy helper

Clearing the 'inet_num' field is necessary and safe if and
only if the socket is not bound. The MPTCP protocol calls
the destroy helper on bound sockets, as tcp_v{4,6}_syn_recv_sock
completed successfully.

Move the clearing of such field out of the common code, otherwise
the MPTCP MP_JOIN error path will find the wrong 'inet_num' value
on socket disposal, __inet_put_port() will acquire the wrong lock
and bind_node removal could race with other modifiers possibly
corrupting the bind hash table.

Reported-and-tested-by: Christoph Paasch <cpaasch@apple.com>
Fixes: 729cd6436f35 ("mptcp: cope better with MP_JOIN failure")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index f40b1b72f979..afaf582a5aa9 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -902,6 +902,7 @@ void inet_csk_prepare_forced_close(struct sock *sk)
 	bh_unlock_sock(sk);
 	sock_put(sk);
 	inet_csk_prepare_for_destroy_sock(sk);
+	inet_sk(sk)->inet_num = 0;
 }
 EXPORT_SYMBOL(inet_csk_prepare_forced_close);