netdev - [PATCH net] mptcp: fix data

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Date:   Wed, 22 Apr 2020 18:24:56 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, mptcp@...ts.01.org
Subject: [PATCH net] mptcp: fix data_fin handing in RX path

The data fin flag is set only via a DSS option, but
mptcp_incoming_options() copies it unconditionally from the
provided RX options.

Since we do not clear all the mptcp sock RX options in a
socket free/alloc cycle, we can end-up with a stray data_fin
value while parsing e.g. MPC packets.

That would lead to mapping data corruption and will trigger
a few WARN_ON() in the RX path.

Instead of adding a costly memset(), fetch the data_fin flag
only for DSS packets - when we always explicitly initialize
such bit at option parsing time.

Fixes: 648ef4b88673 ("mptcp: Implement MPTCP receive path")
Reviewed-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 net/mptcp/options.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index faf57585b892..4a7c467b99db 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -876,12 +876,11 @@ void mptcp_incoming_options(struct sock *sk, struct sk_buff *skb,
 			mpext->data_seq = mp_opt->data_seq;
 			mpext->subflow_seq = mp_opt->subflow_seq;
 			mpext->dsn64 = mp_opt->dsn64;
+			mpext->data_fin = mp_opt->data_fin;
 		}
 		mpext->data_len = mp_opt->data_len;
 		mpext->use_map = 1;
 	}
-
-	mpext->data_fin = mp_opt->data_fin;
 }

 void mptcp_write_options(__be32 *ptr, struct mptcp_out_options *opts)
-- 
2.21.1