[PATCH net-next 5/9] mptcp: hold mptcp socket before calling tcp_done

[Mat Martineau]

From: Florian Westphal <f...@strlen.de>

When processing options from tcp reset path its possible that
tcp_done(ssk) drops the last reference on the mptcp socket which
results in use-after-free.

Reviewed-by: Matthieu Baerts <matthieu.bae...@tessares.net>
Signed-off-by: Florian Westphal <f...@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martin...@linux.intel.com>
---
 net/mptcp/subflow.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index bf808f1fabe5..73e66a406d99 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -313,12 +313,17 @@ void mptcp_subflow_reset(struct sock *ssk)
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        struct sock *sk = subflow->conn;
 
+       /* must hold: tcp_done() could drop last reference on parent */
+       sock_hold(sk);
+
        tcp_set_state(ssk, TCP_CLOSE);
        tcp_send_active_reset(ssk, GFP_ATOMIC);
        tcp_done(ssk);
        if (!test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &mptcp_sk(sk)->flags) &&
            schedule_work(&mptcp_sk(sk)->work))
-               sock_hold(sk);
+               return; /* worker will put sk for us */
+
+       sock_put(sk);
 }
 
 static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
-- 
2.29.2