netdev - [PATCH net 1/3] mptcp: fix opt size when sending DSS + MP

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Date:   Thu,  6 Jan 2022 14:06:36 -0800
From:   Mat Martineau <mathew.j.martineau@...ux.intel.com>
To:     netdev@...r.kernel.org
Cc:     Matthieu Baerts <matthieu.baerts@...sares.net>,
        davem@...emloft.net, kuba@...nel.org, mptcp@...ts.linux.dev,
        pabeni@...hat.com, geliang.tang@...e.com,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>
Subject: [PATCH net 1/3] mptcp: fix opt size when sending DSS + MP_FAIL

From: Matthieu Baerts <matthieu.baerts@...sares.net>

When these two options had to be sent -- which is not common -- the DSS
size was not being taken into account in the remaining size.

Additionally in this situation, the reported size was only the one of
the MP_FAIL which can cause issue if at the end, we need to write more
in the TCP options than previously said.

Here we use a dedicated variable for MP_FAIL size to keep the
WARN_ON_ONCE() just after.

Fixes: c25aeb4e0953 ("mptcp: MP_FAIL suboption sending")
Acked-and-tested-by: Geliang Tang <geliang.tang@...e.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@...sares.net>
Signed-off-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>
---
 net/mptcp/options.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index fe98e4f475ba..96c6efdd48bc 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -821,10 +821,13 @@ bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 	if (mptcp_established_options_mp(sk, skb, snd_data_fin, &opt_size, remaining, opts))
 		ret = true;
 	else if (mptcp_established_options_dss(sk, skb, snd_data_fin, &opt_size, remaining, opts)) {
+		unsigned int mp_fail_size;
+
 		ret = true;
-		if (mptcp_established_options_mp_fail(sk, &opt_size, remaining, opts)) {
-			*size += opt_size;
-			remaining -= opt_size;
+		if (mptcp_established_options_mp_fail(sk, &mp_fail_size,
+						      remaining - opt_size, opts)) {
+			*size += opt_size + mp_fail_size;
+			remaining -= opt_size - mp_fail_size;
 			return true;
 		}
 	}
-- 
2.34.1