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, 30 insertions, 18 deletions

diff --git a/lib/diameter/include/diameter_gen.hrl b/lib/diameter/include/diameter_gen.hrl
index 03aa557c2e..1eb1a8e288 100644
--- a/lib/diameter/include/diameter_gen.hrl
+++ b/lib/diameter/include/diameter_gen.hrl
@@ -227,23 +227,20 @@ decode(Name, #diameter_avp{code = Code, vendor_id = Vid} = Avp, Acc) ->
 
 %% decode/4
 
-%% Don't know this AVP: see if it can be packed in an 'AVP' field
-%% undecoded, unless it's mandatory. Need to give Failed-AVP special
-%% treatment since it'll contain any unrecognized mandatory AVP's.
-decode(Name, 'AVP', #diameter_avp{is_mandatory = M} = Avp, {Avps, Acc}) ->
-    {[Avp | Avps], if M, Name /= 'Failed-AVP' ->
-                           unknown(Avp, Acc);
-                      true ->
-                           pack_AVP(Name, Avp, Acc)
-                   end};
-%% Note that the type field is 'undefined' in this case.
-
-%% Or try to decode.
 decode(Name, {AvpName, Type}, Avp, Acc) ->
-    d(Name, Avp#diameter_avp{name = AvpName, type = Type}, Acc).
+    d(Name, Avp#diameter_avp{name = AvpName, type = Type}, Acc);
+
+decode(Name, 'AVP', Avp, Acc) ->
+    decode_AVP(Name, Avp, Acc).
 
 %% d/3
 
+%% Don't try to decode the value of a Failed-AVP component since it
+%% probably won't.
+d('Failed-AVP' = Name, Avp, Acc) ->
+    decode_AVP(Name, Avp, Acc);
+
+%% Or try to decode.
 d(Name, Avp, {Avps, Acc}) ->
     #diameter_avp{name = AvpName,
                   data = Data}
@@ -265,17 +262,32 @@ d(Name, Avp, {Avps, Acc}) ->
                              ?LINE,
                              {Reason, Avp, erlang:get_stacktrace()}),
             {Rec, Failed} = Acc,
-            {[Avp|Avps], {Rec, [{rc(Reason), Avp} | Failed]}}
+            {[Avp|Avps], {Rec, [rc(Reason, Avp) | Failed]}}
     end.
 
+%% decode_AVP/3
+%%
+%% Don't know this AVP: see if it can be packed in an 'AVP' field
+%% undecoded, unless it's mandatory. Need to give Failed-AVP special
+%% treatment since it'll contain any unrecognized mandatory AVP's.
+%% Note that the type field is 'undefined' in this case.
+
+decode_AVP(Name, #diameter_avp{is_mandatory = M} = Avp, {Avps, Acc}) ->
+    {[Avp | Avps], if Name == 'Failed-AVP';
+                      not M ->
+                           pack_AVP(Name, Avp, Acc);
+                      true ->
+                           unknown(Avp, Acc)
+                   end}.
+
 %% rc/1
 
 %% diameter_types will raise an error of this form to communicate
 %% DIAMETER_INVALID_AVP_LENGTH (5014). A module specified to a
 %% @custom_types tag in a spec file can also raise an error of this
 %% form.
-rc({'DIAMETER', RC, _}) ->
-    RC;
+rc({'DIAMETER', 5014 = RC, _}, #diameter_avp{name = AvpName} = Avp) ->
+    {RC, Avp#diameter_avp{data = empty_value(AvpName)}};
 
 %% 3588:
 %%
@@ -283,8 +295,8 @@ rc({'DIAMETER', RC, _}) ->
 %%      The request contained an AVP with an invalid value in its data
 %%      portion.  A Diameter message indicating this error MUST include
 %%      the offending AVPs within a Failed-AVP AVP.
-rc(_) ->
-    5004.
+rc(_, Avp) ->
+    {5004, Avp}.
 
 %% ungroup/2
 %%