[PATCH 5.10.y 1/3] mptcp: hold mptcp socket before calling tcp_done

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

From: Florian Westphal <fw@strlen.de>

commit ab82e996a1fa1b9ae514fa357d9ce8df62321157 upstream.

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.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: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 2b0f561f21b2 ("mptcp: avoid unneeded actions on subflow reset")
[ Conflicts in subflow.c, because commit 3ba14528684f ("mptcp: avoid
  setting TCP_CLOSE state twice") has already been backported and also
  had the same conflict: this commit here should have been backported
  first. Fixed now! ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 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 c9cf0fdbfbdc..77cc4f585cd8 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -279,11 +279,16 @@ 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_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)
-- 
2.55.0