grml-hostname: reject invalid hostnames

The check doesn't fully verify RFC 952, but it catches some
known-problematic situations and it's better than nothing.

Closes: gf-issue127

Thanks: Evgeni Golov for review

diff --git a/usr_sbin/grml-hostname b/usr_sbin/grml-hostname
index b529d17..b7a6eab 100755 (executable)
--- a/usr_sbin/grml-hostname
+++ b/usr_sbin/grml-hostname
@@ -37,6 +37,20 @@ else
   retval=0
 fi
 
+# stupid + simplified checking for valid hostname (according to RFC 952)
+VALIDATE=$(echo "$NEW_HOSTNAME" | tr --delete '[:alnum:]-')
+if [ -n "$VALIDATE" ] ; then
+  if [ -z "$NONINTERACTIVE" ] ; then
+    dialog --title "${PN}" \
+      --msgbox "Error: invalid characters specified in hostname: '$VALIDATE' can not be used inside hostnames." \
+      0 0
+    exec "$0"
+  else
+    echo "Error: invalid characters specified in hostname: '$VALIDATE' can not be used inside hostnames." >&2
+    exit 1
+  fi
+fi
+
 case $retval in
   0)
      echo "$NEW_HOSTNAME" > /etc/hostname