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Netfilter owner match breakage

DISCUSSION Phil Oester 2 participants 2 messages Aug 27, 2013

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#0 lore raw

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@f19_main ~]$ id
uid=1000(phil) gid=1000(phil) groups=1000(phil)

[phil@f19_main ~]$ sudo iptables -A OUTPUT -p tcp -m owner --uid-owner 1000 -j REJECT

[phil@f19_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

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?

Phil

#1 lore raw
Quoted 10 lines · Phil Oester

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@f19_main ~]$ id
uid=1000(phil) gid=1000(phil) groups=1000(phil)

[phil@f19_main ~]$ sudo iptables -A OUTPUT -p tcp -m owner --uid-owner 1000 -j REJECT

Oh well.

Quoted 8 lines

[phil@f19_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.

Quoted 10 lines

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.