Fix edge cases when specifying the user to run as.

* check the username fits the format expected by adduser;
 * don't allow root;
 * if the user exists, don't try to create it; usually, this is
   harmless, but it fails if the user exists with a UID outside the
   normal range for system users.

Fixes #24.

debian/changelog

@@ -1,3 +1,13 @@
+dump1090-mutability (1.15) UNRELEASED; urgency=medium
+
+  * In development.
+  * Validate that the username given to debconf is syntactically OK and
+    isn't root. (github issue #24)
+  * Don't fail on postinst if the given user exists but is outside
+    the usual system user UID range. (github issue #24)
+
+ -- Oliver Jowett <oliver@mutability.co.uk>  Thu, 19 Feb 2015 22:39:19 +0000
+
 dump1090-mutability (1.14) unstable; urgency=medium
 
   * Position reporting:

debian/dump1090-mutability.config

@@ -69,7 +69,7 @@ db_input_verify() {
   while :
   do
     db_get $KEY
-    if $VERIFY $RET; then return 0; fi
+    if $VERIFY "$RET"; then return 0; fi
     if [ $RESULT -ne 0 ]; then
       # db_input failed, and the existing value does not validate
       if [ $RESULT = 30 ] && [ $ASKED = 0 ]
@@ -161,6 +161,17 @@ is_not_empty() {
   if [ -z "$1" ]; then return 1; else return 0; fi
 }    
 
+# "adduser: To avoid problems, the username should consist only of
+# letters, digits, underscores, full stops, at signs and dashes, and not start with
+# a dash (as defined by IEEE Std 1003.1-2001). For compatibility with Samba
+# machine accounts $ is also supported at the end of the username"
+is_non_root_user() {
+  if [ -z "$1" ]; then return 1;
+  elif [ "$1" = "root" ]; then return 1;
+  elif echo "$1" | grep -Eq '^[a-zA-Z0-9_.@-]+\$?$'; then return 0;
+  else return 1; fi
+}
+
 is_port_number() {
   if is_unsigned_int "$1"; then
     if [ "$1" -eq 0 ]; then return 0; fi
@@ -177,7 +188,7 @@ db_input high $NAME/auto-start || true
 db_go || true; db_get $NAME/auto-start; if [ "$RET" = "true" ]; then
  # all of these are only relevant if the init script is enabled
 
- db_input_verify low $NAME/run-as-user is_not_empty || true
+ db_input_verify low $NAME/run-as-user is_non_root_user || true
  db_input_verify low $NAME/log-file is_not_empty || true
 
  db_input medium $NAME/rtlsdr-device || true

debian/dump1090-mutability.init

@@ -119,7 +119,7 @@ do_start()
             return 2
         fi
 
-	start-stop-daemon --start --quiet --pidfile $PIDFILE --user $DUMP1090_USER --exec $DAEMON --test > /dev/null \
+	start-stop-daemon --start --quiet --pidfile $PIDFILE --user "$DUMP1090_USER" --exec $DAEMON --test > /dev/null \
 		|| return 1
 
         # create JSON_DIR with the appropriate permissions
@@ -130,7 +130,7 @@ do_start()
            fi
         fi
 
-	start-stop-daemon --start $NICELEVEL --quiet --pidfile $PIDFILE --user $DUMP1090_USER --chuid $DUMP1090_USER --make-pidfile --background --no-close --exec $DAEMON -- \
+	start-stop-daemon --start $NICELEVEL --quiet --pidfile $PIDFILE --user "$DUMP1090_USER" --chuid "$DUMP1090_USER" --make-pidfile --background --no-close --exec $DAEMON -- \
 		$ARGS >>$LOGFILE 2>&1 \
 		|| return 2
         sleep 1
@@ -146,7 +146,7 @@ do_stop()
 	#   1 if daemon was already stopped
 	#   2 if daemon could not be stopped
 	#   other if a failure occurred
-	start-stop-daemon --stop --retry=TERM/30/KILL/5 --pidfile $PIDFILE --user $DUMP1090_USER --exec $DAEMON
+	start-stop-daemon --stop --retry=TERM/30/KILL/5 --pidfile $PIDFILE --user "$DUMP1090_USER" --exec $DAEMON
 	RETVAL="$?"
 	[ "$RETVAL" = 2 ] && return 2
         sleep 1

debian/dump1090-mutability.postinst

@@ -97,7 +97,10 @@ case "$1" in
         db_get $NAME/auto-start
         if [ "$RET" = "true" ]; then
           db_get $NAME/run-as-user
-          adduser --system --home /usr/share/$NAME --no-create-home --quiet "$RET"
+          if ! getent passwd "$RET" >/dev/null
+          then
+            adduser --system --home /usr/share/$NAME --no-create-home --quiet "$RET"
+          fi
         fi
 
         # -10 changed the lighttpd config file, but didn't arrange to restart it.

debian/dump1090-mutability.templates

@@ -332,3 +332,7 @@ Type: error
 Template: dump1090-mutability/invalid-is_valid_gain
 Description: Value must be a numeric gain value, or "max", or "agc".
 Type: error
+
+Template: dump1090-mutability/invalid-is_non_root_user
+Description: Value must be a username (without spaces) that isn't root.
+Type: error