On Wed, Mar 20, 2024 at 10:31:00AM +0100, Sven Auhagen wrote:
> On Wed, Mar 20, 2024 at 10:27:30AM +0100, Pablo Neira Ayuso wrote:
> > On Wed, Mar 20, 2024 at 10:20:29AM +0100, Sven Auhagen wrote:
> > > On Wed, Mar 20, 2024 at 10:07:24AM +0100, Pablo Neira Ayuso wrote:
> > > > On Wed, Mar 20, 2024 at 09:49:49AM +0100, Sven Auhagen wrote:
> > > > > On Wed, Mar 20, 2024 at 09:45:16AM +0100, Pablo Neira Ayuso wrote:
> > > > > > Hi Sven,
> > > > > >
> > > > > > On Wed, Mar 20, 2024 at 09:39:16AM +0100, Sven Auhagen wrote:
> > > > > > > On Mon, Mar 18, 2024 at 10:39:15AM +0100, Pablo Neira Ayuso wrote:
> > > > > > [...]
> > > > > > > > diff --git a/net/netfilter/nf_flow_table_core.c b/net/netfilter/nf_flow_table_core.c
> > > > > > > > index a0571339239c..481fe3d96bbc 100644
> > > > > > > > --- a/net/netfilter/nf_flow_table_core.c
> > > > > > > > +++ b/net/netfilter/nf_flow_table_core.c
> > > > > > > > @@ -165,10 +165,22 @@ void flow_offload_route_init(struct flow_offload *flow,
> > > > > > > > }
> > > > > > > > EXPORT_SYMBOL_GPL(flow_offload_route_init);
> > > > > > > >
> > > > > > > > -static void flow_offload_fixup_tcp(struct ip_ct_tcp *tcp)
> > > > > > > > +static s32 flow_offload_fixup_tcp(struct net *net, struct nf_conn *ct,
> > > > > > > > + enum tcp_conntrack tcp_state)
> > > > > > > > {
> > > > > > > > - tcp->seen[0].td_maxwin = 0;
> > > > > > > > - tcp->seen[1].td_maxwin = 0;
> > > > > > > > + struct nf_tcp_net *tn = nf_tcp_pernet(net);
> > > > > > > > +
> > > > > > > > + ct->proto.tcp.state = tcp_state;
> > > > > > > > + ct->proto.tcp.seen[0].td_maxwin = 0;
> > > > > > > > + ct->proto.tcp.seen[1].td_maxwin = 0;
> > > > > > > > +
> > > > > > > > + /* Similar to mid-connection pickup with loose=1.
> > > > > > > > + * Avoid large ESTABLISHED timeout.
> > > > > > > > + */
> > > > > > > > + if (tcp_state == TCP_CONNTRACK_ESTABLISHED)
> > > > > > > > + return tn->timeouts[TCP_CONNTRACK_UNACK];
> > > > > > >
> > > > > > > Hi Pablo,
> > > > > > >
> > > > > > > I tested the patch but the part that sets the timout to UNACK is not
> > > > > > > very practical.
> > > > > > > For example my long running SSH connections get killed off by the firewall
> > > > > > > regularly now while beeing ESTABLISHED:
> > > > > > >
> > > > > > > [NEW] tcp 6 120 SYN_SENT src=192.168.6.55 dst=192.168.10.22 sport=55582 dport=22 [UNREPLIED] src=192.168.10.22 dst=192.168.6.55 sport=22 dport=55582 mark=16777216
> > > > > > > [UPDATE] tcp 6 60 SYN_RECV src=192.168.6.55 dst=192.168.10.22 sport=55582 dport=22 src=192.168.10.22 dst=192.168.6.55 sport=22 dport=55582 mark=16777216
> > > > > > > [UPDATE] tcp 6 86400 ESTABLISHED src=192.168.6.55 dst=192.168.10.22 sport=55582 dport=22 src=192.168.10.22 dst=192.168.6.55 sport=22 dport=55582 [OFFLOAD] mark=16777216
> > > > > > >
> > > > > > > [DESTROY] tcp 6 ESTABLISHED src=192.168.6.55 dst=192.168.10.22 sport=54941 dport=22 packets=133 bytes=13033 src=192.168.10.22 dst=192.168.6.55 sport=22 dport=54941 packets=95 bytes=15004 [ASSURED] mark=16777216 delta-time=1036
> > > > > > >
> > > > > > > I would remove the if case here.
> > > > > >
> > > > > > OK, I remove it and post a v2. Thanks!
> > > > >
> > > > > Thanks and also the hardcoded TCP_CONNTRACK_ESTABLISHED in flow_offload_fixup_ct
> > > > > should be reverted to the real tcp state ct->proto.tcp.state.
> > > >
> > > > ct->proto.tcp.state contains the state that was observed before
> > > > handling over this flow to the flowtable, in most cases, this should
> > > > be TCP_CONNTRACK_ESTABLISHED.
> > > >
> > > > > This way we always set the current TCP timeout.
> > > >
> > > > I can keep it to ct->proto.tcp.state but I wonder if it is better to
> > > > use a well known state such as TCP_CONNTRACK_ESTABLISHED to pick up from.
> > >
> > > In case of a race condition or if something is off like my TCP_FIN
> > > that is beeing offloaded again setting to to ESTABLISHED hard coded
> > > will make the e.g. FIN or CLOSE a very long state.
> > > It is not guaranteed that we are still in ESTABLISHED when this code
> > > runs. Also for example we could have seen both FIN already before the
> > > flowtable gc runs.
> >
> > OK, I just posted a v2, leave things as is. I agree it is better to
> > only address the issue you are observing at this time, it is possible
> > to revisit later.
> >
> > Thanks!
>
> Thanks, I will give it another try.
> I think for it to be foolproof we need
> to migrate the TCP state as well in flow_offload_teardown_tcp to FIN or CLOSE.
My patch already does it:
+void flow_offload_teardown_tcp(struct flow_offload *flow, bool fin)
+{
+ enum tcp_conntrack tcp_state;
+
+ if (fin)
+ tcp_state = TCP_CONNTRACK_FIN_WAIT;
+ else /* rst */
+ tcp_state = TCP_CONNTRACK_CLOSE;
+
+ flow_offload_fixup_tcp(nf_ct_net(flow->ct), flow->ct, tcp_state);
flow_offload_fixup_tcp() updates the TCP state to FIN / CLOSE state.
> They way thinks are right now we are open to a race condition from the reverse side of the
> connection to reoffload the connection while a FIN or RST is not processed by the netfilter code
> running after the flowtable code.
> The conenction is still in TCP established during that window and another packet can just
> push it back to the flowtable while the FIN or RST is not processed yet.
I don't see how:
static void nft_flow_offload_eval(const struct nft_expr *expr,
...
switch (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.protonum) {
case IPPROTO_TCP:
tcph = skb_header_pointer(pkt->skb, nft_thoff(pkt),
sizeof(_tcph), &_tcph);
if (unlikely(!tcph || tcph->fin || tcph->rst ||
!nf_conntrack_tcp_established(ct)))
goto out;
this would now be either in FIN/CLOSE state.
FIN, RST packet does not trigger re-offload. And ACK packet would find
the entry in !nf_conntrack_tcp_established(ct).
What path could trigger re-offload after my latest patch?
For the flow timeout case (where flow entry is released and packets
goes back to classic conntrack path) re-offload is possible, but that
is a feature.
