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Description of problem:
When overlay2 is used as the storage driver for docker any changes made to the permissions of '/' are not taken into account when an image is built.
This is an issue that came up during the investigation of bug 1481808.
Version-Release number of selected component (if applicable):
docker-1.12.6-55.gitc4618fb.el7.x86_64
docker-client-1.12.6-55.gitc4618fb.el7.x86_64
docker-common-1.12.6-55.gitc4618fb.el7.x86_64
How reproducible:
every time
Steps to Reproduce:
1. make sure you are using overlay2 as the storage driver for docker
$ cat /etc/sysconfig/docker-storage
DOCKER_STORAGE_OPTIONS="--storage-driver overlay2 "
2. create a simple dockerfile that changes permissions on '/'
$ cat Dockerfile
FROM rhel7
RUN chmod 0555 /
3. build the image and check the permissions
$ docker build .
$ docker run --rm IMAGEID bash -c "ls -ld /"
drwxr-xr-x. 1 root root 6 Oct 9 10:31
$ docker run --rm IMAGEID bash -c "rpm -V filesystem"
.M....... /
Actual results:
permissions remain unchanged, rpm -V complains
Expected results:
permissions changed to 0555, rpm -V does not complain
Additional info:
Same behaviour when trying to `docker commit` a container that got its permissions on '/' changed.
Seems to be working when 'devicemapper' is used as the storage driver.
I suspect it happens because when overlayfs initializes, for root dentry it takes its certain attrs (uid, gid, mode, ...) from upper directory.
So in this case, after commit, 0555 will be come mode of lower layer. But upper will have some default mode and overlayfs rootfs acquires that.
Not sure what's the intention behind "chmod 555 /". If intention is to not write to layer, anyway it being lower, we never write to it.
If intention is to not allow writes in container rootfs, then I think we need to use that --read-only option of docker.
From my point of view I want the '/' to have 555 just to pass rpm verification of the filesystem package inside the container. The 555 is the default permission it should have and if it does not, rpm complains.
The rpm verification is used as a part of image certifications (and some of our customers run it inside their images) so we should make sure that it passes.
On Fedora 26 I see
[root@localhost test]# rpm -qV filesystem
[root@localhost test]# ls -lZd /
dr-xr-xr-x. 17 root root system_u:object_r:root_t:s0 235 Oct 4 09:44 /
So I guess you are right. I will work on a fix for this.
We have no plans to ship another version of Docker at this time. RHEL7 is in final support stages where only security fixes will get released. Customers should move to use Podman which is available starting in RHEL 7.6.