Merge pull request mirage#117 from hannesm/cleanup-ethif

check length of received ethernet frame (to avoid cstruct exceptions)
samoht · Jul 29, 2015 · 50955dd · 50955dd
2 parents 559e0b9 + b9ee12c
commit 50955dd
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Showing 2 changed files with 31 additions and 20 deletions.
diff --git a/lib/ethif.ml b/lib/ethif.ml
@@ -21,7 +21,6 @@ module Make(Netif : V1_LWT.NETWORK) = struct
 
   type 'a io = 'a Lwt.t
   type buffer = Cstruct.t
-  type ipv4addr = Ipaddr.V4.t
   type macaddr = Macaddr.t
   type netif = Netif.t
 
@@ -40,25 +39,19 @@ module Make(Netif : V1_LWT.NETWORK) = struct
 
   let input ~arpv4 ~ipv4 ~ipv6 t frame =
     MProf.Trace.label "ethif.input";
-    let frame_mac = Macaddr.of_bytes (Wire_structs.copy_ethernet_dst frame) in
-    match frame_mac with
-    | None           -> Lwt.return_unit
-    | Some frame_mac ->
-      if Macaddr.compare frame_mac (mac t) = 0
-         || not (Macaddr.is_unicast frame_mac)
-      then match Wire_structs.get_ethernet_ethertype frame with
-        | 0x0806 -> arpv4 frame (* ARP *)
-        | 0x0800 -> (* IPv4 *)
-          let payload = Cstruct.shift frame Wire_structs.sizeof_ethernet in
-          ipv4 payload
-        | 0x86dd ->
-          let payload = Cstruct.shift frame Wire_structs.sizeof_ethernet in
-          ipv6 payload
-        | _etype ->
-          let _payload = Cstruct.shift frame Wire_structs.sizeof_ethernet in
-          (* TODO default etype payload *)
-          Lwt.return_unit
-      else Lwt.return_unit
+    let of_interest dest =
+      Macaddr.compare dest (mac t) = 0 || not (Macaddr.is_unicast dest)
+    in
+    match Wire_structs.parse_ethernet_frame frame with
+    | Some (typ, destination, payload) when of_interest destination ->
+      begin
+        match typ with
+        | Some Wire_structs.ARP -> arpv4 frame
+        | Some Wire_structs.IPv4 -> ipv4 payload
+        | Some Wire_structs.IPv6 -> ipv6 payload
+        | None -> Lwt.return_unit (* TODO: default ethertype payload handler *)
+      end
+    | _ -> Lwt.return_unit
 
   let write t frame =
     MProf.Trace.label "ethif.write";

diff --git a/lib/wire_structs.ml b/lib/wire_structs.ml
@@ -4,6 +4,24 @@ cstruct ethernet {
     uint16_t       ethertype
   } as big_endian
 
+cenum ethertype {
+    ARP  = 0x0806;
+    IPv4 = 0x0800;
+    IPv6 = 0x86dd;
+  } as uint16_t
+
+let parse_ethernet_frame frame =
+  if Cstruct.len frame >= 14 then
+    (* source + destination + type = 14 *)
+    let payload = Cstruct.shift frame sizeof_ethernet
+    and typ = get_ethernet_ethertype frame
+    and dst = Macaddr.of_bytes_exn (copy_ethernet_dst frame)
+    in
+    Some (int_to_ethertype typ, dst, payload)
+  else
+    None
+
+
 cstruct udp {
     uint16_t source_port;
     uint16_t dest_port;