[Bug 1560623] [NEW] ncat: process Stops in State T after some time

[TJ]

Public bug reported:

On 12.04, 15.10 and 16.04 I'm seeing consistent hangs of ncat when left
running for some time.

In the particular scenario it is proxying a TCP connection as a
background job using:

ncat -m 1 -6kl 10006 | ncat -kl 10007 &

When it stops I see (Here it's explicitly called within a sub-shell):

$ jobs
[4]+  Stopped                 bash -c 'ncat -m 1 -6kl 10006 | ncat -kl 10007'

$ ps -efly | grep ncat
T tj       26816 25874  0  80   0  2436  1296 -      17:42 pts/2    00:00:00 bash -c ncat -m 1 -6kl 10006 | ncat -kl 10007
T tj       26817 26816  0  80   0  1308  1166 -      17:42 pts/2    00:00:00 ncat -m 1 -6kl 10006
T tj       26818 26816  0  80   0  1288  1166 -      17:42 pts/2    00:00:00 ncat -kl 10007

$ sudo grep ^SigQ /proc/2781{7,8}/status
SigQ:   1/7982
SigQ:   1/7982

After attaching gdb to the first process it looks like it is stopped due
to a SIGTTIN signal. Not sure why since the process stdin should be
connected to the listening network socket.

** Affects: nmap (Ubuntu)
     Importance: Undecided
         Status: New

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Title:
  ncat: process Stops in State T after some time

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