netdev - [PATCH net-next] dissector: do not set invalid PPP protocol

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Date:   Wed, 29 Sep 2021 14:32:23 +0300
From:   Boris Sukholitko <boris.sukholitko@...adcom.com>
To:     netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Vladimir Oltean <olteanv@...il.com>,
        Vadym Kochan <vadym.kochan@...ision.eu>,
        Ilya Lifshits <ilya.lifshits@...adcom.com>,
        Boris Sukholitko <boris.sukholitko@...adcom.com>
Subject: [PATCH net-next] dissector: do not set invalid PPP protocol

The following flower filter fails to match non-PPP_IP{V6} packets
wrapped in PPP_SES protocol:

tc filter add dev eth0 ingress protocol ppp_ses flower \
        action simple sdata hi64

The reason is that proto local variable is being set even when
FLOW_DISSECT_RET_OUT_BAD status is returned.

The fix is to avoid setting proto variable if the PPP protocol is unknown.

Signed-off-by: Boris Sukholitko <boris.sukholitko@...adcom.com>
---
 net/core/flow_dissector.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index bac0184cf3de..7d0a9f84aaf7 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1196,9 +1196,8 @@ bool __skb_flow_dissect(const struct net *net,
 			break;
 		}
 
-		proto = hdr->proto;
 		nhoff += PPPOE_SES_HLEN;
-		switch (proto) {
+		switch (hdr->proto) {
 		case htons(PPP_IP):
 			proto = htons(ETH_P_IP);
 			fdret = FLOW_DISSECT_RET_PROTO_AGAIN;
-- 
2.29.2


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