Luca Landi wrote:
Hello everybody, I think I have found a bug with conntracks created by userspace through netlink. The bug resides in the kernel. Basically, when you create a new conntrack through netlink, you normally do so in advance. That is, before any actual packet of that connection arrives (or goes out). (Sidenote: in fact honestly I can't think of situations where one would want to manually create a conntrack truly after the connection to be tracked was already in progress, and also I guess that that would be anyway impossible as such a conntrack would have been created automatically by the kernel). Anyway, as such manual in-advance creation (through netlink) does not go through the L4 initialization normally done by l4proto->new() (as well as all the other things done by init_conntrack()), this at least in the case of a TCP connection does affect tcp_in_window() in that when it sees the first ever packet for that connection (normally the SYN), tcp_in_window() regardlessly goes through the "i-am-in-the-middle-of-a-connection" codepath, not syncing properly with the window. The outcome is that after some kbytes of data transferred, tcp_in_window() starts rejecting packets. In case of nat-ed connections this also means that packets won't be nat-ed any more. Seen all this happening live myself. I already went through the analysis of the relevant kernel code, spotted what happens exactly at every stage, and found (and tested successfully) a possible fix. Just wondered whether you knew this already and had a good argument for it. I know about the "be-liberal-with-windows" flag, which might be considered as a ready workaround, but I thought we could and should do better for this case. What do you think? PS: I'm using ubuntu 8.04 and working with its official kernel. At a superficial glance at the latest stable from kernel.org it seems to me that the problem is still there. Blame me if I am mistaken.
We're automatically enabling the be-liberal logic for picked up connections nowadays, so you shouldn't get out of window packets. Which kernel does ubuntu 8.04 use? -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
