rust/ftp: validate port components in passive reponse

Make sure they are valid 8 bit integers before combining the
two parts into a u16 to prevent an overflow of the u16
return value.

Add unit tests to check parsing of invalid ports.

Redmine issue:
https://redmine.openinfosecfoundation.org/issues/2904

rust/src/ftp/mod.rs

@@ -46,9 +46,9 @@ named!(pub ftp_pasv_response<u16>,
             take_until_and_consume!("(") >>
             digit >> tag!(",") >> digit >> tag!(",") >>
             digit >> tag!(",") >> digit >> tag!(",") >>
-            part1: getu16 >>
+            part1: verify!(getu16, |v| v <= std::u8::MAX as u16) >>
             tag!(",") >>
-            part2: getu16 >>
+            part2: verify!(getu16, |v| v <= std::u8::MAX as u16) >>
             alt! (tag!(").") | tag!(")")) >>
             (
                 part1 * 256 + part2
@@ -108,3 +108,24 @@ pub extern "C" fn rs_ftp_epsv_response(input: *const libc::uint8_t, len: libc::u
     }
     return 0;
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_pasv_response_valid() {
+        let port = ftp_pasv_response("227 Entering Passive Mode (212,27,32,66,221,243).".as_bytes());
+        assert_eq!(port, Ok((&b""[..], 56819)));
+    }
+
+    // A port that is too large for a u16.
+    #[test]
+    fn test_pasv_response_too_large() {
+        let port = ftp_pasv_response("227 Entering Passive Mode (212,27,32,66,257,243).".as_bytes());
+        assert!(port.is_err());
+
+        let port = ftp_pasv_response("227 Entering Passive Mode (212,27,32,66,255,65535).".as_bytes());
+        assert!(port.is_err());
+    }
+}