On Fri, Jan 15, 2016 at 8:21 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> From: Eric Dumazet <edumazet@xxxxxxxxxx>
>
> In case MSS option is added in TCP options, skb length increases by 4.
> IPv6 needs to update skb->csum if skb has CHECKSUM_COMPLETE,
> otherwise kernel complains loudly in netdev_rx_csum_fault() with a
> stack dump.
>
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> ---
> net/netfilter/xt_TCPMSS.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
> index b7c43def0dc6..e118397254af 100644
> --- a/net/netfilter/xt_TCPMSS.c
> +++ b/net/netfilter/xt_TCPMSS.c
> @@ -228,7 +228,7 @@ tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
> {
> struct ipv6hdr *ipv6h = ipv6_hdr(skb);
> u8 nexthdr;
> - __be16 frag_off;
> + __be16 frag_off, oldlen, newlen;
> int tcphoff;
> int ret;
>
> @@ -244,7 +244,12 @@ tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
> return NF_DROP;
> if (ret > 0) {
> ipv6h = ipv6_hdr(skb);
> - ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret);
> + oldlen = ipv6h->payload_len;
> + newlen = htons(ntohs(oldlen) + ret);
> + if (skb->ip_summed == CHECKSUM_COMPLETE)
> + skb->csum = csum_add(csum_sub(skb->csum, oldlen),
> + newlen);
> + ipv6h->payload_len = newlen;
Probably should have a utility function do this. Maybe something like
update_hdr_field(skb, old, new)? Could return new value so above could
just be:
ipv6h->payload_len = update_hdr_field(skb, ipv6h->payload_len,
htons(ntohs(oldlen) + ret);
> }
> return XT_CONTINUE;
> }
>
>
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