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Verify byte counts when handling queries
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Handle lost and duplicate DNS queries.
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@msantos
msantos committed Nov 4, 2010
1 parent 596a84d commit 36d582c
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Showing 2 changed files with 101 additions and 81 deletions.
6 changes: 3 additions & 3 deletions seds/src/seds.erl
View file
Original file line number Diff line number Diff line change
Expand Up @@ -89,11 +89,11 @@ init(Port, Opt) ->


handle_call({send, {IP, Port, #dns_rec{} = Rec,
#seds{type = Type, data = Data} = Query}}, _From,
State) ->
#seds{type = Type, sum = Sum, data = Data} = Query}},
_From, State) ->
Session = seds_protocol:session(Query, map(State)),
{Proxy, Proxies} = proxy(Session, State),
ok = seds_proxy:send(Proxy, IP, Port, Rec, {Type, Data}),
ok = seds_proxy:send(Proxy, IP, Port, Rec, {Type, Sum, Data}),
{reply, ok, State#state{p = Proxies}};

handle_call(Request, _From, State) ->
Expand Down
176 changes: 98 additions & 78 deletions seds/src/seds_proxy.erl
View file
Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,7 @@

sum_up = 0, % number of bytes sent to server
sum_down = 0, % number of bytes received from server
buf = [], % last packet sent (for resend)
data = [<<>>] % list of binaries: data returned by proxied server
}).

Expand All @@ -62,10 +63,10 @@
%%--------------------------------------------------------------------
%%% Interface
%%--------------------------------------------------------------------
send(Pid, IP, Port, #dns_rec{} = Query, {up, Data}) when is_pid(Pid) ->
gen_fsm:send_event(Pid, {up, IP, Port, Query, Data});
send(Pid, IP, Port, #dns_rec{} = Query, {down, _}) when is_pid(Pid) ->
gen_fsm:send_event(Pid, {down, IP, Port, Query}).
send(Pid, IP, Port, #dns_rec{} = Query, {up, Sum, Data}) when is_pid(Pid) ->
gen_fsm:send_event(Pid, {up, IP, Port, Query, Sum, Data});
send(Pid, IP, Port, #dns_rec{} = Query, {down, Sum, _}) when is_pid(Pid) ->
gen_fsm:send_event(Pid, {down, IP, Port, Query, Sum}).

%%--------------------------------------------------------------------
%%% Behaviours
Expand Down Expand Up @@ -148,14 +149,7 @@ connect(timeout, #state{ip = IP, port = Port} = State) ->
%%

% client sent data to be forwarded to server
proxy({up, IP, Port,
#dns_rec{
header = Header,
qdlist = [#dns_query{
domain = Domain,
type = Type
}|_]
} = Rec, Data},
proxy({up, IP, Port, Rec, ClientSum, Data},
#state{
sum_up = Sum,
dnsfd = DNSSocket,
Expand All @@ -165,75 +159,60 @@ proxy({up, IP, Port,
Payload = base32:decode(string:to_upper(Data)),
Sum1 = Sum + length(Payload),

ok = gen_tcp:send(Socket, Payload),

Packet = inet_dns:encode(
Rec#dns_rec{
header = Header#dns_header{
qr = true,
ra = true
},
anlist = [#dns_rr{
domain = Domain,
type = Type,
data = seq(Sum1)
}]
}),

error_logger:info_report([
{direction, up},
{dns_query, Rec}
]),

ok = gen_udp:send(DNSSocket, IP, Port, Packet),
{next_state, proxy, State#state{sum_up = Sum1},
?PROXY_TIMEOUT};

% client requested any pending data from server
case response(up, ClientSum, Sum, Rec) of
error ->
{stop, {up, out_of_sync}, State};
duplicate ->
error_logger:info_report([{dropping, {IP, Port}}]),
{next_state, proxy, State, ?PROXY_TIMEOUT};
Packet ->
error_logger:info_report([
{direction, up},
{dns_query, Packet}
]),
ok = gen_tcp:send(Socket, Payload),
ok = gen_udp:send(DNSSocket, IP, Port, Packet),
{next_state, proxy, State#state{sum_up = Sum1},
?PROXY_TIMEOUT}
end;

% client requested pending data from server
proxy({down, IP, Port,
#dns_rec{
header = Header,
qdlist = [#dns_query{
domain = Domain,
type = Type
}|_]} = Rec},
}|_]} = Rec, ClientSum},
#state{
sum_down = Sum,
dnsfd = DNSSocket,
s = Socket,
data = Data
data = Data,
buf = Buf
} = State) ->

% Client polled, allow more data from server
ok = inet:setopts(Socket, [{active, once}]),

{Payload, Rest} = data(Type, Data),
Sum1 = Sum + length(Payload),

Response = Rec#dns_rec{
header = Header#dns_header{
qr = true,
ra = true
},
anlist = [#dns_rr{
domain = Domain,
type = Type,
data = Payload
}]},
{Payload, Size, Rest} = data(Type, Data),

case response({down, Payload}, ClientSum, Sum, Rec) of
error ->
{stop, {down, out_of_sync}, State};
duplicate ->
error_logger:info_report([{resending, {IP, Port, Sum}}]),
ok = resend(DNSSocket, IP, Port, Type, Buf, Rec),
{next_state, proxy, State#state{sum_down = Sum},
?PROXY_TIMEOUT};
Packet ->
error_logger:info_report([
{direction, down},
{dns_query, Rec}
]),
ok = inet:setopts(Socket, [{active, once}]),
ok = gen_udp:send(DNSSocket, IP, Port, Packet),
{next_state, proxy, State#state{
sum_down = Sum + Size,
data = [Rest],
buf = Data}, ?PROXY_TIMEOUT}
end;

Packet = inet_dns:encode(Response),

error_logger:info_report([
{direction, down},
{dns_query, Rec}
]),

ok = gen_udp:send(DNSSocket, IP, Port, Packet),

{next_state, proxy, State#state{
sum_down = Sum1,
data = [Rest]
}, ?PROXY_TIMEOUT};
proxy(timeout, State) ->
{stop, timeout, State}.

Expand All @@ -245,35 +224,76 @@ seq(N) when is_integer(N) ->
{I1,I2,I3,I4}.


%% Encode the data returned by the server as a DNS record
data(_, [<<>>]) ->
{[],<<>>};
{[],0,<<>>};
data(Type, Data) when is_list(Data) ->
data(Type, list_to_binary(lists:reverse(Data)));

% TXT records
data(txt, <<D1:?MAXDATA/bytes, D2:?MAXDATA/bytes, Rest/binary>>) ->
{[base64:encode_to_string(D1), base64:encode_to_string(D2)], Rest};
{[base64:encode_to_string(D1), base64:encode_to_string(D2)], 2*?MAXDATA, Rest};
data(txt, <<D1:?MAXDATA/bytes, Rest/binary>>) ->
{[base64:encode_to_string(D1)], Rest};
{[base64:encode_to_string(D1)], ?MAXDATA, Rest};
data(txt, Data) ->
{[base64:encode_to_string(Data)], <<>>};
{[base64:encode_to_string(Data)], byte_size(Data), <<>>};

% NULL records
data(null, <<D1:(?MAXDATA*2)/bytes, Rest/binary>>) ->
{base64:encode(D1), Rest};
{base64:encode(D1), ?MAXDATA*2, Rest};
data(null, Data) ->
{base64:encode(Data), <<>>};
{base64:encode(Data), byte_size(Data), <<>>};

% CNAME records
data(cname, <<D1:?MAXDATA/bytes, Rest/binary>>) ->
{label(base32:encode(D1)), Rest};
{label(base32:encode(D1)), ?MAXDATA, Rest};
data(cname, Data) ->
{label(base32:encode(Data)), <<>>}.
{label(base32:encode(Data)), byte_size(Data), <<>>}.


%% Each component (or label) of a CNAME can have a
%% max length of 63 bytes. A "." divides the labels.
label(String) when byte_size(String) < ?MAXLABEL ->
String;
label(String) ->
re:replace(String, ".{63}", "&.", [global, {return, list}]).


%% Packet sum checks
response(up, Sum, Sum, Rec) ->
encode(seq(Sum), Rec);
response({down, Payload}, Sum, Sum, Rec) ->
encode(Payload, Rec);
response(_, Sum1, Sum2, _) when Sum1 < Sum2 ->
duplicate;
response(_, Sum1, Sum2, _) when Sum1 > Sum2 ->
error.


%% Encode the DNS response to the client
encode(Data, #dns_rec{
header = Header,
qdlist = [#dns_query{
domain = Domain,
type = Type
}|_]} = Rec) ->
inet_dns:encode(Rec#dns_rec{
header = Header#dns_header{
qr = true,
ra = true
},
anlist = [#dns_rr{
domain = Domain,
type = Type,
data = Data
}]}).


% Resend a lost packet
resend(_Socket, _IP, _Port, _Type, [], _Rec) ->
ok;
resend(Socket, IP, Port, Type, Data, Rec) ->
{Payload, _, _} = data(Type, Data),
gen_udp:send(Socket, IP, Port, encode(Payload, Rec)).


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