icmpv4_socket: correct the IPv4 total_length field

On some OSes (particularly macOS) the IP header returned to userspace has a bogus total length (e.g. 16384). This probably reflects an internal kernel buffer size rather than the on-the-wire size of the original packet. This patch corrects the IPv4 header total length so that the IPv4 parser can parse the result. Previously it would return an Error. Signed-off-by: David Scott <[email protected]>
mirage · Aug 8, 2017 · e08cf5e · e08cf5e
1 parent e7fe08c
commit e08cf5e
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/src/stack-unix/icmpv4_socket.ml b/src/stack-unix/icmpv4_socket.ml
@@ -97,6 +97,12 @@ let listen _t addr fn =
         recvfrom' fd receive_buffer [] >>= fun (len, _sockaddr) ->
         (* trim the buffer to the amount of data actually received *)
         let receive_buffer = Cstruct.set_len receive_buffer len in
+        (* On macOS the IP length field is set to a very large value (16384) which
+           probably reflects some kernel datastructure size rather than the real
+           on-the-wire size. This confuses our IPv4 parser so we correct the size
+           here. *)
+        let len = Ipv4_wire.get_ipv4_len receive_buffer in
+        Ipv4_wire.set_ipv4_len receive_buffer (min len (Cstruct.len receive_buffer));
         Lwt.async (fun () -> fn receive_buffer);
         loop ()
       in