Re: [REGRESSION] NFS is creating a hidden port (left over from xs_bind() )

[Trond Myklebust]

On Thu, Jun 11, 2015 at 11:49 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> I recently upgraded my main server to 4.0.4 from 3.19.5 and rkhunter
> started reporting a hidden port on my box.
>
> Running unhide-tcp I see this:
>
> # unhide-tcp
> Unhide-tcp 20121229
> Copyright  2012 Yago Jesus & Patrick Gouin
> License GPLv3+ : GNU GPL version 3 or later
> http://www.unhide-forensics.info
> Used options:
> [*]Starting TCP checking
>
> Found Hidden port that not appears in ss: 946
> [*]Starting UDP checking
>
> This scared the hell out of me as I'm thinking that I have got some kind
> of NSA backdoor hooked into my server and it is monitoring my plans to
> smuggle Kinder Ãberraschung into the USA from Germany. I panicked!
>
> Well, I wasted the day writing modules to first look at all the sockets
> opened by all processes (via their file descriptors) and posted their
> port numbers.
>
>   http://rostedt.homelinux.com/private/tasklist.c
>
> But this port wasn't there either.
>
> Then I decided to look at the ports in tcp_hashinfo.
>
>   http://rostedt.homelinux.com/private/portlist.c
>
> This found the port but no file was connected to it, and worse yet,
> when I first ran it without using probe_kernel_read(), it crashed my
> kernel, because sk->sk_socket pointed to a freed socket!
>
> Note, each boot, the hidden port is different.
>
> Finally, I decided to bring in the big guns, and inserted a
> trace_printk() into the bind logic, to see if I could find the culprit.
> After fiddling with it a few times, I found a suspect:
>
>    kworker/3:1H-123   [003] ..s.    96.696213: inet_bind_hash: add 946
>
> Bah, it's a kernel thread doing it, via a work queue. I then added a
> trace_dump_stack() to find what was calling this, and here it is:
>
>     kworker/3:1H-123   [003] ..s.    96.696222: <stack trace>
>  => inet_csk_get_port
>  => inet_addr_type
>  => inet_bind
>  => xs_bind
>  => sock_setsockopt
>  => __sock_create
>  => xs_create_sock.isra.18
>  => xs_tcp_setup_socket
>  => process_one_work
>  => worker_thread
>  => worker_thread
>  => kthread
>  => kthread
>  => ret_from_fork
>  => kthread
>
> I rebooted, and examined what happens. I see the kworker binding that
> port, and all seems well:
>
> # netstat -tapn |grep 946
> tcp        0      0 192.168.23.9:946        192.168.23.22:55201     ESTABLISHED -
>
> But waiting for a bit, the connection goes into a TIME_WAIT, and then
> it just disappears. But the bind to the port does not get released, and
> that port is from then on, taken.
>
> This never happened with my 3.19 kernels. I would bisect it but this is
> happening on my main server box which I usually only reboot every other
> month doing upgrades. It causes too much disturbance for myself (and my
> family) as when this box is offline, basically the rest of my machines
> are too.
>
> I figured this may be enough information to see if you can fix it.
> Otherwise I can try to do the bisect, but that's not going to happen
> any time soon. I may just go back to 3.19 for now, such that rkhunter
> stops complaining about the hidden port.
>

The only new thing that we're doing with 4.0 is to set SO_REUSEPORT on
the socket before binding the port (commit 4dda9c8a5e34: "SUNRPC: Set
SO_REUSEPORT socket option for TCP connections"). Perhaps there is an
issue with that?

Cheers
  Trond
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