Re: nf_ct_ftp: dropping packet: partial matching of `227 '

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Cc'ing netfilter@ too
Thread: https://lists.fedoraproject.org/archives/list/kernel@xxxxxxxxxxxxxxxxxxxxxxx/thread/CLNQ6O6OGNEJAFFSNV56KU6P2JAPM5YU/

Em 16-04-2016 10:52, Reindl Harald escreveu:

Am 15.04.2016 um 10:16 schrieb Reindl Harald:
Am 14.04.2016 um 23:53 schrieb Marcelo Ricardo Leitner:
Otherwise it won't be able to expect the new connection

sounds reasonable, on the other side the client yesterday had troubles
to make passive ftp connections with "connection refused" as far as the
admin was able to tell on the phone

It could be that the drop happened and an auxiliary connection was
attempted before the retransmission of the 227 reply, so your firewall
didn't know about it and actively blocked the connection. If it had
silently dropped the new connection request, the client probably would
retransmit the SYN after a bit.

Now why the cameras are triggering it, good question

not the cameras - a ordinary client with filezilla, that one with 227 in
his IP address, the cameras blow their images without any problem on the
FTP server

maybe i made it not clear enough:

there is no "my firewall" between that is just iptables directly on the
machine running pure-ftpd and so it's killing outgoing localhost traffic
- that is very weird

Okay but expected :) because even if conntrack is running on the system itself that is running the service, it ignores that fact and still acts like just a man-in-the-middle.

So you can still reproduce it? If so, I don't see another way to debug this but to unload nf_conntrack_ftp and take a traffic capture without limiting the packet size (don't use -s option), because I'm afraid that otherwise conntrack will drop the packet and we won't even see it in the capture. Look for a packet containing a "227 " in the beginning of TCP payload. That should be our guy.
Feel free to send it only to my email if you prefer.

Unfortunately the pr_debug()s available on that area aren't much helpful for this problem.

And which kernel is this?

  Marcelo
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