Bug 2111275

@dguthrie can I ask for a few more details please?  At first blush, it looks like you may have not volume mounted /mycache.  Can you please let us know:

1)  Were you running this a root or a rootless user
2)  What was the buildah command that you used?

Hi @tsweeney and @arajan 

The initial command was this:

$ buildah build --layers=true  -t localhost/testlayers:v1 .

I had to used --cap-add to have it allow strace. I did try it with setenforce 0 and 1. There are no messages that show up in the selinux logs.

$ buildah build --layers=true  -t localhost/testlayers:v1 --cap-add SYS_PTRACE .

Okay, it does work if I set use both ",z" and set the user to root

~~~
FROM ubi8/ubi

ARG UID=0
ARG GID=0

USER ${UID}:${GID}
RUN --mount=type=cache,uid=${UID},gid=${GID},target=/mycache,z touch /mycache/test.txt
RUN --mount=type=cache,uid=${UID},gid=${GID},target=/mycache,z mkdir -p /mycache/foo/bar
~~~

If I change the user ID to something else, like 1000, it fails.

Hi @arajan,

One thing I did notice is that if I run it once with the 'z' flag, then I can thereafter take the z flag off and it will still work with that same cached path. It seems to be reusing the same cached pat, but remembering the how it was created (i.e. z) rather than treating the path with the 'z' and different than the one without.

What I mean is

RUN --mount=type=cache,uid=${UID},gid=${GID},target=/mycache touch /mycache/test.txt

-- Permission denied

RUN --mount=type=cache,uid=${UID},gid=${GID},target=/mycache,z touch /mycache/test.txt

-- Success

RUN --mount=type=cache,uid=${UID},gid=${GID},target=/mycache touch /mycache/test.txt

-- Success

Where the UID is 0, of course.