Re: [PATCH 4.19.y] netfilter: nft_payload: do not update layer 4 checksum when mangling fragments

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Fri, Jan 28, 2022 at 12:38:21PM +0100, Florian Westphal wrote:
> 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>
> ---
>  This is already in the 5.y branches but 4.19 needs a minor
>  tweak as ->fragoff member resides in xt sub-struct.

Thanks for taking care of this -stable submission.

>  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 b1a9f330a51f..fd87216bc0a9 100644
> --- a/net/netfilter/nft_payload.c
> +++ b/net/netfilter/nft_payload.c
> @@ -194,6 +194,9 @@ static int nft_payload_l4csum_offset(const struct nft_pktinfo *pkt,
>  				     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);
> -- 
> 2.34.1
>