Fix recognition of 5014 (INVALID_AVP_LENGTH) errors

Invalid lengths come in two flavours: ones that correctly point at the
end of an AVP's payload but don't agree with its type, and ones that
point elsewhere. The former are relatively harmless but the latter leave
no way to recover AVP boundaries, which typically results in failure to
decode subsequent AVP's in the message in question.

In the case that AVP Length points past the end of the message, diameter
incorrectly regarded the error as 5009, INVALID_AVP_BITS: not right
since the error has nothing to do with AVP Flags. Ditto if the length
was less than 8, a minimal header length. Only in the remaining case was
the detected error 5014, INVALID_AVP_LENGTH. However, in this case it
slavishly followed RFC 3588 in suggesting the undecodable AVP as
Failed-AVP, thereby passing the woeful payload back to the sender to
have equal difficulty decoding. Now follow RFC 6733 and suggest an AVP
with a zero-filled payload.

1 files changed, 5 insertions, 6 deletions

diff --git a/lib/diameter/src/base/diameter_traffic.erl b/lib/diameter/src/base/diameter_traffic.erl
index 1ba5cf0b3e..4733b67131 100644
--- a/lib/diameter/src/base/diameter_traffic.erl
+++ b/lib/diameter/src/base/diameter_traffic.erl
@@ -226,10 +226,10 @@ recv_R(false = No, _, _, _, _) ->  %% transport has gone down
 
 collect_avps(Pkt) ->
     case diameter_codec:collect_avps(Pkt) of
-        {_Bs, As} ->
-            As;
-        As ->
-            As
+        {_Error, Avps} ->
+            Avps;
+        Avps ->
+            Avps
     end.
 
 %% recv_R/6
@@ -300,7 +300,7 @@ errors(_, #diameter_packet{header = #diameter_header{version = V},
 %%      AVP's definition.
 
 errors(_, #diameter_packet{errors = [Bs | Es]} = Pkt)
-  when is_bitstring(Bs) ->
+  when is_bitstring(Bs) ->  %% from old code
     Pkt#diameter_packet{errors = [3009 | Es]};
 
 %%   DIAMETER_COMMAND_UNSUPPORTED       3001
@@ -595,7 +595,6 @@ reply([Msg], Dict, TPid, Dict0, Fs, ReqPkt)
        is_tuple(Msg) ->
     reply(Msg, Dict, TPid, Dict0, Fs, ReqPkt#diameter_packet{errors = []});
 
-%% No errors or a diameter_header/avp list.
 reply(Msg, Dict, TPid, Dict0, Fs, ReqPkt) ->
     Pkt = encode(Dict, reset(make_answer_packet(Msg, ReqPkt), Dict), Fs),
     incr(send, Pkt, Dict, TPid, Dict0),  %% count outgoing result codes