libcap binaries missing (obeone#3)

* alpine version cappimg + fixing missing libcap bin

* Improved method to check SYS_ADMIN capability

Author: obeone

Dockerfile

@@ -1,9 +1,8 @@
-ARG BUILD_FROM=alpine:latest
+ARG BUILD_FROM=alpine:3.17
 
 FROM $BUILD_FROM
 
-RUN apk --update --no-cache add bash nfs-utils && \
-                                                  \
+RUN apk --update --no-cache add bash nfs-utils libcap-utils && \
     # remove the default config files
     rm -v /etc/idmapd.conf /etc/exports
 

entrypoint.sh

@@ -277,7 +277,7 @@ is_kernel_module_loaded() {
 
 is_granted_linux_capability() {
 
-  if capsh --print | grep -Eq "^Current: = .*,?${1}(,|$)"; then
+  if capsh --decode=$(grep CapBnd /proc/$$/status|cut -f2) | grep cap_sys_admin > /dev/null; then
     return 0
   fi