Russell King (Oracle) <linux@xxxxxxxxxxxxxxx> wrote: [..] > Digging through the tcpdump and logs, it seems what is going on is: > > public interface dmz interface > origin -> mailserver SYN origin -> mailserver SYN > mailserver -> origin SYNACK mailserver -> origin SYNACK > origin -> mailserver ACK > mailserver -> origin RST > mailserver -> origin SYNACK mailserver -> origin SYNACK > mailserver -> origin SYNACK mailserver -> origin SYNACK > mailserver -> origin SYNACK mailserver -> origin SYNACK > mailserver -> origin SYNACK mailserver -> origin SYNACK > ... > > Here is an example from the public interface: > > 09:52:36.599398 IP 103.14.225.112.63461 > 78.32.30.218.587: Flags [SEW], seq 3387227814, win 8192, options [mss 1460,nop,wscale 8,nop,nop,sackOK], length 0 > 09:52:36.599893 IP 78.32.30.218.587 > 103.14.225.112.63461: Flags [S.], seq 816385329, ack 3387227815, win 64240, options [mss 1452,nop,nop,sackOK,nop,wscale 7], length 0 > 09:52:36.820464 IP 103.14.225.112.63461 > 78.32.30.218.587: Flags [.], ack 1, win 260, length 0 > 09:52:36.820549 IP 78.32.30.218.587 > 103.14.225.112.63461: Flags [R], seq 816385330, win 0, length 0 > 09:52:37.637548 IP 78.32.30.218.587 > 103.14.225.112.63461: Flags [S.], seq 816385329, ack 3387227815, win 64240, options [mss 1452,nop,nop,sackOK,nop,wscale 7], length 0 > > and the corresponding trace on the mailserver: > 09:52:36.599729 IP 103.14.225.112.63461 > 78.32.30.218.587: Flags [SEW], seq 3387227814, win 8192, options [mss 1452,nop,wscale 8,nop,nop,sackOK], length 0 > 09:52:36.599772 IP 78.32.30.218.587 > 103.14.225.112.63461: Flags [S.], seq 816385329, ack 3387227815, win 64240, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 > 09:52:37.637421 IP 78.32.30.218.587 > 103.14.225.112.63461: Flags [S.], seq 816385329, ack 3387227815, win 64240, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 > > So, my first observation is that conntrack is reacting to the ACK > packet on the public interface, and marking the connection established, > but a firewall rule is rejecting the connection when that ACK packet is > received by sending a TCP reset. It looks like conntrack does not see > this packet, Right, this is silly. I'll see about this; the rst packet bypasses conntrack because nf_send_reset attaches the exising entry of the packet its replying to -- tcp conntrack gets skipped for the generated RST. But this is also the case in 5.16, so no idea why this is surfacing now.
