Fix mismatching src ip address in TCP socket transmissions

src/iface/interface/mod.rs

@@ -574,6 +574,7 @@ impl Interface {
 
         enum EgressError {
             Exhausted,
+            MismatchedSrcIp,
             Dispatch,
         }
 
@@ -589,6 +590,12 @@ impl Interface {
             let mut neighbor_addr = None;
             let mut respond = |inner: &mut InterfaceInner, meta: PacketMeta, response: Packet| {
                 neighbor_addr = Some(response.ip_repr().dst_addr());
+
+                if !inner.has_ip_addr(response.ip_repr().src_addr()) {
+                    net_debug!("failed to transmit IP: mismatched src addr");
+                    return Err(EgressError::MismatchedSrcIp);
+                }
+
                 let t = device.transmit(inner.now).ok_or_else(|| {
                     net_debug!("failed to transmit IP: device exhausted");
                     EgressError::Exhausted
@@ -638,13 +645,20 @@ impl Interface {
                     })
                 }
                 #[cfg(feature = "socket-tcp")]
-                Socket::Tcp(socket) => socket.dispatch(&mut self.inner, |inner, (ip, tcp)| {
+                Socket::Tcp(socket) => match socket.dispatch(&mut self.inner, |inner, (ip, tcp)| {
                     respond(
                         inner,
                         PacketMeta::default(),
                         Packet::new(ip, IpPayload::Tcp(tcp)),
                     )
-                }),
+                }) {
+                    Err(EgressError::MismatchedSrcIp) => {
+                        // FIXME: Should this be `close()` or `abort()`?
+                        socket.reset();
+                        Err(EgressError::MismatchedSrcIp)
+                    }
+                    r => r,
+                },
                 #[cfg(feature = "socket-dhcpv4")]
                 Socket::Dhcpv4(socket) => {
                     socket.dispatch(&mut self.inner, |inner, (ip, udp, dhcp)| {
@@ -677,6 +691,7 @@ impl Interface {
                         neighbor_addr.expect("non-IP response packet"),
                     );
                 }
+                Err(EgressError::MismatchedSrcIp) => {},
                 Ok(()) => {}
             }
         }

src/socket/tcp.rs

@@ -812,7 +812,7 @@ impl<'a> Socket<'a> {
         self.state
     }
 
-    fn reset(&mut self) {
+    pub fn reset(&mut self) {
         let rx_cap_log2 =
             mem::size_of::<usize>() * 8 - self.rx_buffer.capacity().leading_zeros() as usize;