netdev - [PATCH net 4/4] netfilter: flowtable: fix tcp and udp header checksum update

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Message-Id: <20210205001727.2125-5-pablo@netfilter.org>
Date:   Fri,  5 Feb 2021 01:17:27 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org, kuba@...nel.org
Subject: [PATCH net 4/4] netfilter: flowtable: fix tcp and udp header checksum update

From: Sven Auhagen <sven.auhagen@...eatech.de>

When updating the tcp or udp header checksum on port nat the function
inet_proto_csum_replace2 with the last parameter pseudohdr as true.
This leads to an error in the case that GRO is used and packets are
split up in GSO. The tcp or udp checksum of all packets is incorrect.

The error is probably masked due to the fact the most network driver
implement tcp/udp checksum offloading. It also only happens when GRO is
applied and not on single packets.

The error is most visible when using a pppoe connection which is not
triggering the tcp/udp checksum offload.

Fixes: ac2a66665e23 ("netfilter: add generic flow table infrastructure")
Signed-off-by: Sven Auhagen <sven.auhagen@...eatech.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 net/netfilter/nf_flow_table_core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_flow_table_core.c b/net/netfilter/nf_flow_table_core.c
index 513f78db3cb2..4a4acbba78ff 100644
--- a/net/netfilter/nf_flow_table_core.c
+++ b/net/netfilter/nf_flow_table_core.c
@@ -399,7 +399,7 @@ static int nf_flow_nat_port_tcp(struct sk_buff *skb, unsigned int thoff,
 		return -1;
 
 	tcph = (void *)(skb_network_header(skb) + thoff);
-	inet_proto_csum_replace2(&tcph->check, skb, port, new_port, true);
+	inet_proto_csum_replace2(&tcph->check, skb, port, new_port, false);
 
 	return 0;
 }
@@ -415,7 +415,7 @@ static int nf_flow_nat_port_udp(struct sk_buff *skb, unsigned int thoff,
 	udph = (void *)(skb_network_header(skb) + thoff);
 	if (udph->check || skb->ip_summed == CHECKSUM_PARTIAL) {
 		inet_proto_csum_replace2(&udph->check, skb, port,
-					 new_port, true);
+					 new_port, false);
 		if (!udph->check)
 			udph->check = CSUM_MANGLED_0;
 	}
-- 
2.20.1