abuild: add safety check so we dont scan elfs outside our pkgdir

this is to catch bugs in abuild itself early

abuild.in

@@ -1039,13 +1039,21 @@ find_scanelf_paths() {
 
 scan_shared_objects() {
 	local name="$1" controldir="$2" datadir="$3"
-	local opt=
+	local opt= i=
 
 	# allow spaces in paths
 	IFS=:
 	set -- $(find_scanelf_paths "$datadir")
 	unset IFS
 
+	# sanity check, verify that each path is prefixed with datadir
+	for i; do
+		if [ "${i#$datadir}" = "$i" ]; then
+			error "Internal error in scanelf paths"
+			return 1
+		fi
+	done
+
 	if options_has "ldpath-recursive"; then
 		opt="--recursive"
 	fi