netdev - [PATCH net] flow_dissector: do not dissect l4 ports for fragments

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Date:   Fri,  9 Nov 2018 16:53:06 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        배석진 <soukjin.bae@...sung.com>
Subject: [PATCH net] flow_dissector: do not dissect l4 ports for fragments

From: 배석진 <soukjin.bae@...sung.com>

Only first fragment has the sport/dport information,
not the following ones.

If we want consistent hash for all fragments, we need to
ignore ports even for first fragment.

This bug is visible for IPv6 traffic, if incoming fragments
do not have a flow label, since skb_get_hash() will give
different results for first fragment and following ones.

It is also visible if any routing rule wants dissection
and sport or dport.

See commit 5e5d6fed3741 ("ipv6: route: dissect flow
in input path if fib rules need it") for details.

[edumazet] rewrote the changelog completely.

Fixes: 06635a35d13d ("flow_dissect: use programable dissector in skb_flow_dissect and friends")
Signed-off-by: 배석진 <soukjin.bae@...sung.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/flow_dissector.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 676f3ad629f95625422aa55f0f54157001ac477c..588f475019d47c9d6bae8883acebab48aaf63b48 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1166,8 +1166,8 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		break;
 	}
 
-	if (dissector_uses_key(flow_dissector,
-			       FLOW_DISSECTOR_KEY_PORTS)) {
+	if (dissector_uses_key(flow_dissector, FLOW_DISSECTOR_KEY_PORTS) &&
+	    !(key_control->flags & FLOW_DIS_IS_FRAGMENT)) {
 		key_ports = skb_flow_dissector_target(flow_dissector,
 						      FLOW_DISSECTOR_KEY_PORTS,
 						      target_container);
-- 
2.19.1.930.g4563a0d9d0-goog