[PATCH 4.19 08/86] netfilter: nft_payload: do not update layer 4 checksum when mangling fragments

Greg Kroah-Hartman
2022-02-07T11:25:09Z

From: Pablo Neira Ayuso <pablo@netfilter.org>

commit 4e1860a3863707e8177329c006d10f9e37e097a8 upstream.

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@weinreich.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/netfilter/nft_payload.c | 3 +++
1 file changed, 3 insertions(+)

--- a/net/netfilter/nft_payload.c
+++ b/net/netfilter/nft_payload.c
@@ -194,6 +194,9 @@ static int nft_payload_l4csum_offset(con
struct sk_buff *skb,
unsigned int *l4csum_offset)
{
+ if (pkt->xt.fragoff)
+ return -1;
+
switch (pkt->tprot) {
case IPPROTO_TCP:
*l4csum_offset = offsetof(struct tcphdr, check);