test-volume-permissions.sh

#!/bin/bash

cat > Dockerfile << EOF
FROM debian:jessie

ENV APPDIR=/srv/app
VOLUME \$APPDIR
WORKDIR \$APPDIR

RUN \
  groupadd -g 1000 appgrp &&\
  groupadd -g 1001 secgrp &&\
  useradd -u 1000 -g 1000 -Ms /bin/bash appusr &&\
  useradd -u 1001 -g 1001 -Ms /bin/bash secusr &&\
  true
EOF

docker build -t permtest .

echo ">> Creating a secret file as the secret user"
docker run --rm -it \
  -v `pwd`:/srv/app \
  -u secusr \
  permtest \
  sh -c "echo imsecret > secret.txt && chmod 0600 secret.txt && ls -l secret.txt"

echo ">> Attempting to read the secret file as the unprivileged user"
docker run --rm -it \
  -v `pwd`:/srv/app \
  -u appusr \
  permtest \
  sh -c "ls -l secret.txt && cat secret.txt"