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

[Eric Dumazet]

On Fri, 2015-06-12 at 10:10 -0400, Trond Myklebust wrote:
> 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?

Strange, because the usual way to not have time-wait is to use SO_LINGER
with linger=0

And apparently xs_tcp_finish_connecting() has this :

                sock_reset_flag(sk, SOCK_LINGER);
                tcp_sk(sk)->linger2 = 0;

Are you sure SO_REUSEADDR was not the thing you wanted ?

Steven, have you tried kmemleak ?



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