Re: Possible conntrack/kernel bug - not catching certain ICMP packets

[Ed W <lists@wildgooses.com>]

Please, could someone take a look at this possible conntrack issue?
Even just acknowledging that it's reproducible on a selection of recent
kernels or architectures would help?

Thanks

Ed W


>> Essentially we have a reproducible situation where conntrack is
>> (apparently) relating a packet to a connection, but not incrementing the
>> connection counters?
>>
>> Thanks for any help figuring out a fix?
>>
>> Ed W
>>
>>
>> On 15/07/2011 12:45, Ed W wrote:
>>> Hi, This is related to a previous thread, but more complete problem
>>> statement below:
>>>
>>> I notice that I can get an ICMP packet to bypass parts of conntrack
>>> under the following conditions
>>>
>>> - Send a UDP packet that triggers some kind of UDP reply
>>> - Close the listening UDP socket before that reply arrives
>>> - Kernel generates an ICMP unreachable response which does not appear to
>>> be tracked (as expected) by conntrack
>>>
>>> Tested with kernel 2.6.38.4 + iptables 1.4.11.1
>>>
>>> Reproduce this easily like so:
>>>
>>>     nslookup www.yahoo.co.uk 8.8.8.8 & sleep 0.001 && killall nslookup
>>>
>>>     (where the sleep obviously needs to be smaller than your DNS RTT
>>> lookup time. Obviously substitute nslookup/dig as appropriate...)
>>>
>>> My results
>>>
>>> # conntrack -E
>>>
>>>     [NEW] udp      17 30 src=10.141.86.7 dst=8.8.8.8 sport=60721
>>> dport=53 [UNREPLIED] src=8.8.8.8 dst=10.141.86.7 sport=53 dport=60721
>>>  [UPDATE] udp      17 29 src=10.141.86.7 dst=8.8.8.8 sport=60721
>>> dport=53 src=8.8.8.8 dst=10.141.86.7 sport=53 dport=60721
>>> [DESTROY] udp      17 src=10.141.86.7 dst=8.8.8.8 sport=60721 dport=53
>>> packets=1 bytes=66 src=8.8.8.8 dst=10.141.86.7 sport=53 dport=60721
>>> packets=1 bytes=110
>>>
>>> # tcpdump
>>>
>>> 11:26:35.072564 IP 10.141.86.7.60721 > 8.8.8.8.domain: 2+ PTR?
>>> 8.8.8.8.in-addr.arpa. (38)
>>> 11:26:35.351804 IP 8.8.8.8.domain > 10.141.86.7.60721: 2 1/0/0 PTR
>>> google-public-dns-a.google.com. (82)
>>> 11:26:35.352110 IP 10.141.86.7 > 8.8.8.8: ICMP 10.141.86.7 udp port
>>> 60721 unreachable, length 118
>>>
>>>
>>> # iptables -A OUTPUT -j LOGMARK
>>> # iptables -A OUTPUT -j LOG
>>>
>>> Jul 15 11:26:35 localhost kern.warn kernel: [ 6676.964396] iif=0
>>> hook=OUTPUT nfmark=0x0 secmark=0x0 classify=0x0 ctdir=ORIGINAL
>>> ct=0xcf3d5060 ctmark=0x0 ctstate=NEW ctstatus= lifetime=6346s
>>> Jul 15 11:26:35 localhost kern.warn kernel: [ 6676.964396] IN= OUT=ppp1
>>> SRC=10.141.86.7 DST=8.8.8.8 LEN=66 TOS=0x00 PREC=0x00 TTL=64 ID=19971 DF
>>> PROTO=UDP SPT=60721 DPT=53 LEN=46
>>> Jul 15 11:26:35 localhost kern.warn kernel: [ 6677.249312] iif=0
>>> hook=OUTPUT nfmark=0x0 secmark=0x0 classify=0x0 ctdir=ORIGINAL
>>> ct=0xcf3d5060 ctmark=0x0 ctstate=RELATED ctstatus=SEEN_REPLY,CONFIRMED
>>> lifetime=4294937s
>>> Jul 15 11:26:35 localhost kern.warn kernel: [ 6677.249426] IN= OUT=ppp1
>>> SRC=10.141.86.7 DST=8.8.8.8 LEN=138 TOS=0x00 PREC=0xC0 TTL=64 ID=18412
>>> PROTO=ICMP TYPE=3 CODE=3 [SRC=8.8.8.8 DST=10.141.86.7 LEN=110 TOS=0x00
>>> PREC=0x00 TTL=46 ID=3897 PROTO=UDP SPT=53 DPT=60721 LEN=90
>>>
>>>
>>> Notice that logmark seems to show that the ctstatus on the ICMP packet 
>>> is SEEN_REPLY, but conntrack -E shows only packets=1?  tcpdump shows
>>> that the ICMP packet did indeed go out
>>>
>>> Could someone with more knowledge of conntrack please investigate further? 
>>>
>>> Thanks
>>>
>>> Ed W
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe netfilter" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe netfilter" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
> 
> --
> To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html