Ensure that `--userns=keep-id` sets user in config

One of the side-effects of the `--userns=keep-id` command is
switching the default user of the container to the UID of the
user running Podman (though this can still be overridden by the
`--user` flag). However, it did this by setting the UID and GID
in the OCI spec, and not by informing Libpod of its intention to
switch users via the `WithUser()` option. Because of this, a lot
of the code that should have triggered when the container ran
with a non-root user was not triggering. In the case of the issue
that this fixed, the code to remove capabilities from non-root
users was not triggering. Adjust the keep-id code to properly
inform Libpod of our intention to use a non-root user to fix
this.

Also, fix an annoying race around short-running exec sessions
where Podman would always print a warning that the exec session
had already stopped.

Fixes #9919

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

1 files changed, 10 insertions, 0 deletions

diff --git a/pkg/specgen/generate/namespaces.go b/pkg/specgen/generate/namespaces.go
index 845dfdad7..b52e8d100 100644
--- a/pkg/specgen/generate/namespaces.go
+++ b/pkg/specgen/generate/namespaces.go
@@ -157,6 +157,16 @@ func namespaceOptions(ctx context.Context, s *specgen.SpecGenerator, rt *libpod.
 	case specgen.KeepID:
 		if rootless.IsRootless() {
 			toReturn = append(toReturn, libpod.WithAddCurrentUserPasswdEntry())
+
+			// If user is not overridden, set user in the container
+			// to user running Podman.
+			if s.User == "" {
+				_, uid, gid, err := util.GetKeepIDMapping()
+				if err != nil {
+					return nil, err
+				}
+				toReturn = append(toReturn, libpod.WithUser(fmt.Sprintf("%d:%d", uid, gid)))
+			}
 		} else {
 			// keep-id as root doesn't need a user namespace
 			s.UserNS.NSMode = specgen.Host