This ended up more complicated then expected. Lets start first with the
problem to show why I am doing this:
Currently we simply execute ps(1) in the container. This has some
drawbacks. First, obviously you need to have ps(1) in the container
image. That is no always the case especially in small images. Second,
even if you do it will often be only busybox's ps which supports far
less options.
Now we also have psgo which is used by default but that only supports a
small subset of ps(1) options. Implementing all options there is way to
much work.
Docker on the other hand executes ps(1) directly on the host and tries
to filter pids with `-q` an option which is not supported by busybox's
ps and conflicts with other ps(1) arguments. That means they fall back
to full ps(1) on the host and then filter based on the pid in the
output. This is kinda ugly and fails short because users can modify the
ps output and it may not even include the pid in the output which causes
an error.
So every solution has a different drawback, but what if we can combine
them somehow?! This commit tries exactly that.
We use ps(1) from the host and execute that in the container's pid
namespace.
There are some security concerns that must be addressed:
- mount the executable paths for ps and podman itself readonly to
prevent the container from overwriting it via /proc/self/exe.
- set NO_NEW_PRIVS, SET_DUMPABLE and PDEATHSIG
- close all non std fds to prevent leaking files in that the caller had
open
- unset all environment variables to not leak any into the contianer
Technically this could be a breaking change if somebody does not
have ps on the host and only in the container but I find that very
unlikely, we still have the exec in container fallback.
Because this can be insecure when the contianer has CAP_SYS_PTRACE we
still only use the podman exec version in that case.
This updates the docs accordingly, note that podman pod top never falls
back to executing ps in the container as this makes no sense with
multiple containers so I fixed the docs there as well.
Fixes#19001
Fixes https://bugzilla.redhat.com/show_bug.cgi?id=2215572
Signed-off-by: Paul Holzinger <pholzing@redhat.com>
597ebeb60f