handle PPP opts with broken sub-options encoding

Protocol options are optional and 3GPP TS 29.060 says that optional,
invalid IEs should be silently ignored. Do just that.

src/gtp_packet.erl

@@ -444,7 +444,10 @@ decode_protocol_opts(<<Id:16, Length:8, Data:Length/bytes, Next/binary>>, Protoc
     Opt = decode_protocol_ppp_opt(Id, Data),
     decode_protocol_opts(Next, Protocol, [Opt | Opts]);
 decode_protocol_opts(<<Id:16, Length:8, Data:Length/bytes, Next/binary>>, Protocol, Opts) ->
-    decode_protocol_opts(Next, Protocol, [{Id, Data} | Opts]).
+    decode_protocol_opts(Next, Protocol, [{Id, Data} | Opts]);
+decode_protocol_opts(<<_Id:16, Length:8, Data/binary>> = Raw, Protocol, Opts)
+  when Length > byte_size(Data) ->
+    decode_protocol_opts(<<>>, Protocol, [{raw, Raw} | Opts]).
 
 decode_array_of_seq_no(Array) ->
     [X || <<X:16/integer>> <= Array].
@@ -801,6 +804,8 @@ encode_protocol_config_opts({Protocol, Opts}) ->
 
 encode_protocol_opts(_Protocol, [], Opts) ->
     Opts;
+encode_protocol_opts(Protocol, [{raw, Raw} | T], Opts) ->
+    encode_protocol_opts(Protocol, T, <<Opts/binary, Raw/binary>>);
 encode_protocol_opts(Protocol, [{Id, Data} | T], Opts)
   when Id < 16#8000; Id >= 16#FF00 ->
     encode_protocol_opts(Protocol, T, <<Opts/binary, Id:16, (size(Data)):8, Data/binary>>);

test/gtp_SUITE.erl

@@ -120,6 +120,14 @@ test_messages() ->
                  "00850004ac1410a8850004ac1410a9870004000b921f")},
      {{v1, pco_rel97},
       hexstr2bin("3215000A0003A8F4696E0000018084000100")},
+     {{v1, broken_protocol_opts},
+      hexstr2bin("3210009e000000009c3d00000225053590694975f40337f020fffeff0eb20ffc"
+                 "1003591521110359151f1405800002f12183000403746e3184001d80c0230601"
+                 "000006000080c7d7566a4e82b050d1cee3780ed5431c000085000442c9bffe85"
+                 "000442c9bffe860008915689051092544787000f0213921f7396fefe742affff"
+                 "008e0094000160970001019800080137f0204e30409a99000269009a00085389"
+                 "758054936010")},
+
      {{v2, echo_request},
       hexstr2bin("40010009006a50000300010073")},