[lxc-users] Possible race condition in kernel, capset() fails randomly

[Vladimir Pouzanov]

Docker starts lxc in the following way:

lxc-start -n
97a0813ce28954250aaa807567c9053e3e443a8651791e9c591572b0850095af
/.dockerinit -driver lxc -g 172.17.42.1 -i 172.17.0.2/16 -mtu 1500 --
/bin/true

strace of lxc-start: https://gist.github.com/farcaller/6fd5b23952675aed894d

it doesn't seem to run ./dockerinit in case of failure.


On Tue, Jun 3, 2014 at 8:14 PM, Serge Hallyn <serge.hallyn at ubuntu.com>
wrote:

> Quoting Vladimir Pouzanov (farcaller at gmail.com):
> > This bug happens with docker, but I don't see any traction on my issue
> over
> > there so trying to escalate further. The original bug report is here:
> > https://github.com/dotcloud/docker/issues/4556, here are all the
> > interesting details.
> >
> > I'm running an armv7 box (wandboard) with 3.14.4-1-ARCH kernel. I cannot
> > reliably use docker (with lxc driver, or with native driver) as it
> crashes
> > often (on the last docker/lxc/kernel combo I get 41 out of 100 failures
> > with native docker and 23 out of 100 with lxc).
> >
> > The lxc version is 1.0.3, docker is 0.11.1.
> >
> > From docker side the error looks like:
> > finalize namespace drop capabilities operation not permitted
> >
> > (generated by docker capabilities module,
> >
> https://github.com/dotcloud/docker/blob/master/pkg/libcontainer/security/capabilities/capabilities.go#L32
> > )
> >
> > lxc-start just silently returns 1 and I didn't manage to get any
> reasonable
> > log output from it.
>
> How did you use lxc-start exactly?
>
> > I managed to look a bit deeper into kernel side of things on what is
> > failing exactly, and the offending syscall seems to be:
> >
> > https://github.com/torvalds/linux/blob/master/kernel/capability.c#L240
> >
> > where pid is always 1 and task_pid_vnr(current) is 7, sometimes 6,
> rarely 1
> > (the good case).
>
> You'll probably want to get init to run under strace so you can figure out
> why current is pid 7 instead of 1.  What binary is it actually that's doing
> the capset?
>
> > Any ideas on what could be going wrong? What other info can I provide to
> > track this bug down?
> >
> > --
> > Sincerely,
> > Vladimir "Farcaller" Pouzanov
> > http://farcaller.net/
>
> > _______________________________________________
> > lxc-users mailing list
> > lxc-users at lists.linuxcontainers.org
> > http://lists.linuxcontainers.org/listinfo/lxc-users
>
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-- 
Sincerely,
Vladimir "Farcaller" Pouzanov
http://farcaller.net/
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