From: Shayan Pooya <shayan@liveve.org>
To: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: piping core dump to a program escapes container
Date: Sat, 24 Oct 2015 14:54:35 -0700 [thread overview]
Message-ID: <CABAubTgj8+xngrvc7sNbYS_Hq+-rGAYCz0y433ByiZ45dZuT0w@mail.gmail.com> (raw)
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).
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).
next reply other threads:[~2015-10-24 21:54 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-24 21:54 Shayan Pooya [this message]
2015-11-01 20:25 ` piping core dump to a program escapes container Richard Weinberger
2015-11-05 4:42 ` Shayan Pooya
2015-12-09 2:26 ` Dongsheng Yang
2015-12-09 2:36 ` Dongsheng Yang
2015-12-09 3:29 ` Eric W. Biederman
2015-12-09 5:53 ` Dongsheng Yang
2015-12-09 6:32 ` Eric W. Biederman
2015-12-09 8:06 ` Dongsheng Yang
2015-12-09 8:34 ` Bruno Prémont
2015-12-10 0:27 ` Dongsheng Yang
2015-12-10 2:58 ` Dongsheng Yang
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