BUG in tty_open when using containers and ptrace

Grzegorz Nosek root at localdomain.pl
Tue Jul 14 03:31:29 PDT 2009

On pon, lip 13, 2009 at 11:49:05 -0700, Sukadev Bhattiprolu wrote:
> Grzegorz Nosek [root at localdomain.pl] wrote:
> | Simply run it as container init. Sometimes it oopses immediately,
> I am trying to reproduce this too and just trying to make sure I get
> your environment correctly.  I have just built/installed libvirt 0.6.5
> on Ubuntu 9.04. 

0.6.4 or 0.6.5, no difference really (tested both). Host distro is
Debian Lenny but Ubuntu is probably close enough. Didn't test distro
kernel, only used hand-built 2.6.30, and 2.6.31-rc2

> The bug does require libvirt+kvm right ?  IOW, does this simple test repro
> if it is run as a container-init with say lxc-start (i.e from liblxc - see
> http://lxc.sourceforge.net/) ? Another simpler way to create container-init
> is the ns_exec program - I assume that won't create the problem ?

Probably, as it requires a "cross-namespace" pty. I didn't yet set up a
lxc config file. Maybe you can help off the top of your head with the
right incantations? BTW, where's the canonical source for ns_exec?

> Also in an earlier mail you mentioned that disabling the 'newinstance'
> mount option to devpts did not help. So does your setup work with older
> kernels like 2.6.28 ?

Well, I failed to build 2.6.28 with NET_NS (even without SYSFS it wasn't
available in menuconfig) but 2.6.29 exhibits very similar behaviour,
i.e. crashes instantly. The difference is that when the pty master
exits, container init receives a SIGHUP. If it chooses to ignore it and
open /dev/console anyway, *boom*. Looking roughly at %eip and the
faulting address, it's the same bug.

Best regards,
 Grzegorz Nosek

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