linux-kernel - [PATCH 5.16 0419/1039] mptcp: fix opt size when sending DSS + MP

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Message-Id: <20220124184139.391651474@linuxfoundation.org>
Date:   Mon, 24 Jan 2022 19:36:48 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>,
        Geliang Tang <geliang.tang@...e.com>
Subject: [PATCH 5.16 0419/1039] mptcp: fix opt size when sending DSS + MP_FAIL

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

[ Upstream commit 04fac2cae9422a3401c172571afbcfdd58fa5c7e ]

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>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 fe98e4f475baa..96c6efdd48bcc 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