netdev - [PATCH net 3/4] netfilter: nft_payload: do not update layer 4 checksum when mangling fragments

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Message-Id: <20220106215139.170824-4-pablo@netfilter.org>
Date:   Thu,  6 Jan 2022 22:51:38 +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 3/4] netfilter: nft_payload: do not update layer 4 checksum when mangling fragments

IP fragments do not come with the transport header, hence skip bogus
layer 4 checksum updates.

Fixes: 1814096980bb ("netfilter: nft_payload: layer 4 checksum adjustment for pseudoheader fields")
Reported-and-tested-by: Steffen Weinreich <steve@...nreich.org>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 net/netfilter/nft_payload.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
index bd689938a2e0..58e96a0fe0b4 100644
--- a/net/netfilter/nft_payload.c
+++ b/net/netfilter/nft_payload.c
@@ -546,6 +546,9 @@ static int nft_payload_l4csum_offset(const struct nft_pktinfo *pkt,
 				     struct sk_buff *skb,
 				     unsigned int *l4csum_offset)
 {
+	if (pkt->fragoff)
+		return -1;
+
 	switch (pkt->tprot) {
 	case IPPROTO_TCP:
 		*l4csum_offset = offsetof(struct tcphdr, check);
-- 
2.30.2