netdev - Re: Netfilter owner match breakage

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Message-ID: <1377636211.8828.152.camel@edumazet-glaptop>
Date:	Tue, 27 Aug 2013 13:43:31 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Phil Oester <kernel@...uxace.com>
Cc:	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
	edumazet@...gle.com
Subject: Re: Netfilter owner match breakage

On Tue, 2013-08-27 at 13:24 -0700, Phil Oester wrote:
> In commit 90ba9b19 (tcp: tcp_make_synack() can use alloc_skb()), Eric changed
> the call to sock_wmalloc in tcp_make_synack to alloc_skb.  In doing so,
> the netfilter owner match lost its ability to block the SYNACK packet on
> outbound listening sockets.  For example:
> 
> [phil@..._main ~]$ id
> uid=1000(phil) gid=1000(phil) groups=1000(phil)
> 
> [phil@..._main ~]$ sudo iptables -A OUTPUT -p tcp -m owner --uid-owner 1000 -j REJECT
> 

Oh well.

> [phil@..._main ~]$ echo hi | nc -l -p 8888
> 
> Before this commit, attempting to connect to the port 8888 listener generated
> this:
> 
> 10.10.10.1.47457 > 10.10.10.110.8888: Flags [S], seq 1855270582 [...]
> 10.10.10.110 > 10.10.10.110: ICMP 10.10.10.1 tcp port 47457 unreachable, length 68
> 

Hmm... I think TCP stack should send more SYNACK, no ?

It sounds more logical to block the incoming SYN, but whatever.

> After this commit, the session is established but the first packet of the
> session gets rejected:
> 
> 10.10.10.1.47453 > 10.10.10.110.8888: Flags [S], seq 2089355862 [...]
> 10.10.10.110.8888 > 10.10.10.1.47453: Flags [S.], seq 2554257713, ack 2089355863 [...]
> 10.10.10.1.47453 > 10.10.10.110.8888: Flags [.], ack 1, win 115 [...]
> 10.10.10.110 > 10.10.10.110: ICMP 10.10.10.1 tcp port 47453 unreachable, length 63
> 
> Reverting 90ba9b19 (and adjusting for the removal of s_data_desired) fixes the
> problem.  Is there a better way to do this?

Well, a revert seems OK to me, it was not a critical change.


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