Eric Dumazet wrote: > > > On 03/08/2018 02:08 AM, Serhey Popovych wrote: >> We can't use skb_reset_transport_header() together with skb_put() to set >> skb->transport_header field because skb_put() does not touch skb->data. >> >> Do this same way as we did for csum_data in code: substract skb->head >> from tcph. >> >> Signed-off-by: Serhey Popovych <serhe.popovych@xxxxxxxxx> >> --- >> net/ipv4/netfilter/ipt_SYNPROXY.c | 8 ++++---- >> net/ipv6/netfilter/ip6t_SYNPROXY.c | 8 ++++---- >> 2 files changed, 8 insertions(+), 8 deletions(-) >> >> diff --git a/net/ipv4/netfilter/ipt_SYNPROXY.c >> b/net/ipv4/netfilter/ipt_SYNPROXY.c >> index f75fc6b..4953390 100644 >> --- a/net/ipv4/netfilter/ipt_SYNPROXY.c >> +++ b/net/ipv4/netfilter/ipt_SYNPROXY.c >> @@ -90,8 +90,8 @@ >> niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr); >> - skb_reset_transport_header(nskb); >> nth = skb_put(nskb, tcp_hdr_size); >> + nskb->transport_header = (unsigned char *)nth - nskb->head; > > I have no idea why you believe the current code is not correct. > alloc_skb(): skb->head = skb->data = skb_tail_pointer(skb) synproxy_build_ip(): skb_reset_network_header() /* skb_network_header(skb) == skb->data */ skb_put(skb, len); /* skb->tail += len; skb->len += len */ > nth = skb_put() : nth is equal to skb->data Yes it is equal to skb->data, but in my opinion should be set to skb->data + ip_hdrlen(skb) to point to TCP header. > > So skb_reset_transport_header(nskb); does exactly the same thing than > your code, but in a more readable way, without ugly cast. Yes I also not happy with this cast. >
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