dtls: Correct error handling for fragment reassembling

Author: IngelaAndin

lib/ssl/src/dtls_handshake.erl

@@ -318,24 +318,33 @@ address_to_bin({A,B,C,D,E,F,G,H}, Port) ->
     <<A:16,B:16,C:16,D:16,E:16,F:16,G:16,H:16,Port:16>>.
 
 %%--------------------------------------------------------------------
-
 handle_fragments(Version, FragmentData, Buffers0, Options, Acc) ->
-    Fragments = decode_handshake_fragments(FragmentData),
-    do_handle_fragments(Version, Fragments, Buffers0, Options, Acc).
+    try decode_handshake_fragments(FragmentData) of
+        Fragments ->
+            do_handle_fragments(Version, Fragments, Buffers0, Options, Acc)
+    catch
+        error:_Reason ->
+            throw(?ALERT_REC(?FATAL, ?DECODE_ERROR, malformed_handshake_fragment))
+    end.
 
 do_handle_fragments(_, [], Buffers, _Options, Acc) ->
     {lists:reverse(Acc), Buffers};
-do_handle_fragments(Version, [Fragment | Fragments], Buffers0, #{log_level := LogLevel} = Options, Acc) ->
-    case reassemble(Version, Fragment, Buffers0) of
-	{more_data, Buffers} when Fragments == [] ->
-	    {lists:reverse(Acc), Buffers};
-	{more_data, Buffers} ->
-	    do_handle_fragments(Version, Fragments, Buffers, Options, Acc);
-	{{Handshake, _} = HsPacket, Buffers} ->
+do_handle_fragments(Version, [Fragment | Fragments], Buffers0,
+                    #{log_level := LogLevel} = Options, Acc) ->
+    try reassemble(Version, Fragment, Buffers0) of
+        {more_data, Buffers} when Fragments == [] ->
+            {lists:reverse(Acc), Buffers};
+        {more_data, Buffers} ->
+            do_handle_fragments(Version, Fragments, Buffers, Options, Acc);
+        {{Handshake, _} = HsPacket, Buffers} ->
             ssl_logger:debug(LogLevel, inbound, 'handshake', Handshake),
-	    do_handle_fragments(Version, Fragments, Buffers, Options, [HsPacket | Acc])
+            do_handle_fragments(Version, Fragments, Buffers, Options, [HsPacket | Acc])
+    catch
+        error:_Reason ->
+            throw(?ALERT_REC(?FATAL, ?DECODE_ERROR, malformed_handshake_fragment))
     end.
 
+
 decode_handshake(Version, <<?BYTE(Type), Bin/binary>>) ->
     decode_handshake(Version, Type, Bin).
 
@@ -379,7 +388,7 @@ decode_tls_handshake(Version, Tag, Msg) ->
     ssl_handshake:decode_handshake(TLSVersion, Tag, Msg).
 
 decode_handshake_fragments(<<>>) ->
-    [<<>>];
+    [];
 decode_handshake_fragments(<<?BYTE(Type), ?UINT24(Length),
 			     ?UINT16(MessageSeq),
 			     ?UINT24(FragmentOffset), ?UINT24(FragmentLength),