`kubectl cp` relies on tar to extract the copied file/directory in the
container, tar by default attempts to chown/chmod the extracted file
after extraction if the user is the "superuser"(root)
```
--same-owner
try extracting files with the same ownership as exists in the archive
(default for superuser)
-p, --preserve-permissions, --same-permissions
extract information about file permissions (default for superuser)
```
This fails in environment where the container runs as root but is not
granted the OWNER or CHOWN capability.
Before this patch below was the behavior of `kubectl cp`
```
kubectl cp README.md foo-67b6fcbd4c-qjlt6:/tmp
tar: README.md: Cannot change ownership to uid 1000, gid 1000: Operation
not permitted
tar: Exiting with failure status due to previous errors
command terminated with exit code 2
kubectl exec -it foo-67b6fcbd4c-qjlt6 -- ls -l /tmp/README.md
-rw------- 1 1000 1000 3179 Oct 7 22:00 /tmp/README.md
```
After this patch
```
kubectl cp -x a foo-67b6fcbd4c-qjlt6:/
kubectl exec -it foo-67b6fcbd4c-qjlt6 -- ls -l /tmp/README.md
-rw-r--r-- 1 root root 3179 Oct 7 22:00 /tmp/README.md
```
Adds an extra check condition for "." in stripPathShortcuts
so that an empty string is returned, and the correct prefix
index is used untarAll when generating path names.
Resolves: #69804.
