mbuto: UID 0 doesn't mean we're root, check uid_map too

Make mbuto run as expected in a detached user namespace: we'll still
need to use fakeroot(1), change $PATH, and we can't use fusermount(1)
to keep the CPIO archive mounted.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/mbuto b/mbuto
index 7530c72..0609e7e 100755
--- a/mbuto
+++ b/mbuto
@@ -1210,7 +1210,14 @@ usage() {
 
 
 # If we're not running as root, re-run with fakeroot
-if [ "${LD_PRELOAD}" != "libfakeroot-sysv.so" ] && [ "$(id -u)" -ne 0 ]; then
+if [ "$(id -u)" -eq 0 ] && \
+   [ "$(cat /proc/self/uid_map)" = "         0          0 4294967295" ]; then
+	__as_root=1
+else
+	__as_root=0
+fi
+
+if [ "${LD_PRELOAD}" != "libfakeroot-sysv.so" ] && [ ${__as_root} -eq 0 ]; then
 	if ! FAKEROOT="$(command -v fakeroot)"; then
 		__fakeroot_missing="y"
 	else