Re: piping core dump to a program escapes container

[Dongsheng Yang]

On 12/09/2015 10:26 AM, Dongsheng Yang wrote:
> On 10/25/2015 05:54 AM, Shayan Pooya wrote:
> > I noticed the following core_pattern behavior in my linux box while
> > running docker containers. I am not sure if it is bug, but it is
> > inconsistent and not documented.
> >
> > If the core_pattern is set on the host, the containers will observe
> > and use the pattern for dumping cores (there is no per cgroup
> > core_pattern). According to core(5) for setting core_pattern one can:
> >
> > 1. echo "/tmp/cores/core.%e.%p" > /proc/sys/kernel/core_pattern
> > 2. echo "|/bin/custom_core /tmp/cores/ %e %p " >
> > /proc/sys/kernel/core_pattern
> >
> > The former pattern evaluates the /tmp/cores path in the container's
> > filesystem namespace. Which means, the host does not see a core file
> > in /tmp/cores.
> >
> > However, the latter evaluates the /bin/custom_core path in the global
> > filesystem namespace. Moreover, if /bin/core decides to write the core
> > to a path (/tmp/cores in this case as shown by the arg to
> > custom_core), the path will be evaluated in the global filesystem
> > namespace as well.
> >
> > The latter behaviour is counter-intuitive and error-prone as the
> > container can fill up the core-file directory which it does not have
> > direct access to (which means the core is also not accessible for
> > debugging if someone only has access to the container).
>
> Hi Shayan,
>      We found the same problem with what you described here.
> Is there any document for this behaviour? I want to know is
> that intentional or as you said a 'bug'. Maybe that's intentional
> to provide a way for admin to collect core dumps from all containers as
> Richard said. I am interested in it too.
>
> Anyone can help here?

In addition, is that a good idea to make core_pattern to be seperated
in different namespace?

Yang
> Yang
> > Currently, I work around this issue by detecting that the process is
> > crashing from a container (by comparing the namespace pid to the
> > global pid) and refuse to dump the core if it is from a container.
> >
> > Tested on Ubuntu (kernel 3.16) and Fedora (kernel 4.1).
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>
>
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