Jason Xing <kerneljasonxing@xxxxxxxxx> wrote:
> client_ip:client_port <--> server_ip:b_port
>
> Then, some strange skbs from client or gateway, say, out-of-window
> skbs are sent to the server_ip:a_port (not b_port) due to DNAT
> clearing skb->_nfct value in nf_conntrack_in() function. Why?
> Because the tcp_in_window() considers the incoming skb as an
> invalid skb by returning NFCT_TCP_INVALID.
So far everything is as intended.
> I think, even we have set DNAT policy, it would be better if the
> whole process/behaviour adheres to the original TCP behaviour.
>
> Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
> ---
> net/netfilter/nf_conntrack_proto_tcp.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
> index ae493599a3ef..3f3e620f3969 100644
> --- a/net/netfilter/nf_conntrack_proto_tcp.c
> +++ b/net/netfilter/nf_conntrack_proto_tcp.c
> @@ -1253,13 +1253,11 @@ int nf_conntrack_tcp_packet(struct nf_conn *ct,
> res = tcp_in_window(ct, dir, index,
> skb, dataoff, th, state);
> switch (res) {
> - case NFCT_TCP_IGNORE:
> - spin_unlock_bh(&ct->lock);
> - return NF_ACCEPT;
> case NFCT_TCP_INVALID:
> nf_tcp_handle_invalid(ct, dir, index, skb, state);
> + case NFCT_TCP_IGNORE:
> spin_unlock_bh(&ct->lock);
> - return -NF_ACCEPT;
> + return NF_ACCEPT;
This looks wrong. -NF_ACCEPT means 'pass packet, but its not part
of the connection' (packet will match --ctstate INVALID check).
This change disables most of the tcp_in_window() test, this will
pretend everything is fine even though tcp_in_window says otherwise.
You could:
- drop invalid tcp packets in input hook
- set nf_conntrack_tcp_be_liberal=1
both will avoid this 'rst' issue.
