vxlan: fix port-range attribute marshalling

Since we were not updating the `buffer` variable when writing to it, the "max"
part of the range was over-writing the "min", which caused the netlink message
to be considered invalid.

By adjusting the buffer to where we write, the netlink add message was
properly processed, and the link successfully created.

Unit tests were added to assert the expected behavior.

Signed-off-by: Miguel Duarte Barroso <[email protected]>

src/rtnl/link/nlas/link_infos.rs

@@ -782,7 +782,7 @@ impl Nla for InfoVxlan {
             Port(ref value) => BigEndian::write_u16(buffer, *value),
             PortRange(ref range) => {
                 BigEndian::write_u16(buffer, range.0);
-                BigEndian::write_u16(buffer, range.1)
+                BigEndian::write_u16(&mut buffer[2..], range.1)
             }
         }
     }
@@ -2498,4 +2498,52 @@ mod tests {
         nlas.as_slice().emit(&mut vec);
         assert_eq!(&vec[..], &VXLAN[..]);
     }
+
+    lazy_static! {
+        static ref VXLAN_INFO_WITH_PORT_RANGE: Vec<InfoVxlan> =
+            vec![InfoVxlan::Id(10), InfoVxlan::PortRange((9000, 9050)),];
+    }
+
+    #[rustfmt::skip]
+    static VXLAN_WITH_PORT_RANGE: [u8; 32] = [
+        0x0a, 0x00, // length = 10
+        0x01, 0x00, // type = 1 = IFLA_INFO_KIND
+            0x76, 0x78, 0x6C, 0x61, 0x6E, // V = "vxlan\0"
+            0x00, 0x00, 0x00, // padding
+        0x14, 0x00, // length = 20
+        0x02, 0x00, // type = 2 = IFLA_INFO_DATA
+            0x08, 0x00, // length - 8
+            0x01, 0x00, // type = 1 = IFLA_VXLAN_ID
+                0x0A, 0x00, // id = 0x0A = 10
+                0x00, 0x00, // padding
+            0x08, 0x00, // length = 6
+            0x0A, 0x00, // type = 10 = IFLA_VXLAN_PORT_RANGE
+                0x23, 0x28, // min port: 9000
+                0x23, 0x5a  // max port: 9050
+    ];
+
+    #[test]
+    fn emit_info_vxlan_with_port_range() {
+        let nlas = vec![
+            Info::Kind(InfoKind::Vxlan),
+            Info::Data(InfoData::Vxlan(VXLAN_INFO_WITH_PORT_RANGE.clone())),
+        ];
+
+        assert_eq!(nlas.as_slice().buffer_len(), VXLAN_WITH_PORT_RANGE.len());
+
+        let mut vec = vec![0xff; VXLAN_WITH_PORT_RANGE.len()];
+        nlas.as_slice().emit(&mut vec);
+        assert_eq!(&vec[..], &VXLAN_WITH_PORT_RANGE[..]);
+    }
+
+    #[test]
+    fn parse_info_vxlan_with_port_range() {
+        let nla = NlaBuffer::new_checked(&VXLAN_WITH_PORT_RANGE[..]).unwrap();
+        let parsed = VecInfo::parse(&nla).unwrap().0;
+        let expected = vec![
+            Info::Kind(InfoKind::Vxlan),
+            Info::Data(InfoData::Vxlan(VXLAN_INFO_WITH_PORT_RANGE.clone())),
+        ];
+        assert_eq!(expected, parsed);
+    }
 }