mptcp: fix NULL pointer dereference on fastopen early fallback

In case of early fallback to TCP, subflow_syn_recv_sock() deletes
the subflow context before returning the newly allocated sock to
the caller.

The fastopen path does not cope with the above unconditionally
dereferencing the subflow context.

Fixes: 36b122baf6a8 ("mptcp: add subflow_v(4,6)_send_synack()")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/fastopen.c b/net/mptcp/fastopen.c
index d237d142171c5a96b13ef459832fc988fa2f5401..bceaab8dd8e460e7a3459e12af6089ab6bb6b2b7 100644 (file)
--- a/net/mptcp/fastopen.c
+++ b/net/mptcp/fastopen.c
@@ -9,11 +9,18 @@
 void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subflow,
                                              struct request_sock *req)
 {
-       struct sock *ssk = subflow->tcp_sock;
-       struct sock *sk = subflow->conn;
+       struct sock *sk, *ssk;
        struct sk_buff *skb;
        struct tcp_sock *tp;
 
+       /* on early fallback the subflow context is deleted by
+        * subflow_syn_recv_sock()
+        */
+       if (!subflow)
+               return;
+
+       ssk = subflow->tcp_sock;
+       sk = subflow->conn;
        tp = tcp_sk(ssk);
 
        subflow->is_mptfo = 1;