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manage fcnt (#1003)
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* don't set max to 0 for these cases

That would refuse all future copies of this packet because they exceeded
the multi-buy. We want the rest of the already purchased packets to come
through okay.

* multi buy is primarily done in hpr

don't re-check here, the packet was bought, let's use it

* don't blanket update device fcnt from the packet

This already happens deeper in this call graph when the packet is
accepted and used

* remove 32 bit rollover test

the max 32bit frame count is somewhere in the 4billions.
the highest frame count for a device in use here is ~1,800,000.
136 years has about 4billion seconds.

* return verified_fcnt when finding device for data

The device_worker will be provided with the verified fcnt rather than
the expected fcnt when handling a packet.

* differentiate finding device for join and data

* remove inactive devices that are chosen during routing

* export as helper

* rename, uplink is more easily recognizable over data

* bring back updating the device fcnt

A verified frame count is being provided here rather than a speculative
frame count.
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@michaeldjeffrey
michaeldjeffrey authored Oct 9, 2023
1 parent b74710c commit 9b2baeb
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Showing 4 changed files with 66 additions and 254 deletions.
5 changes: 5 additions & 0 deletions src/device/router_device.erl
View file
Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@
dev_eui/1, dev_eui/2,
keys/1, keys/2,
nwk_s_key/1,
nwk_s_keys/1,
app_s_key/1,
devaddr/1,
devaddrs/1, devaddrs/2,
Expand Down Expand Up @@ -125,6 +126,10 @@ nwk_s_key(#device_v7{keys = []}) ->
nwk_s_key(#device_v7{keys = [{NwkSKey, _AppSKey} | _]}) ->
NwkSKey.

-spec nwk_s_keys(device()) -> list(binary()).
nwk_s_keys(#device_v7{keys = Keys}) ->
[NwkSKey || {NwkSKey, _AppSKey} <- Keys].

-spec app_s_key(device()) -> binary() | undefined.
app_s_key(#device_v7{keys = []}) ->
undefined;
Expand Down
177 changes: 51 additions & 126 deletions src/device/router_device_routing.erl
View file
Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,8 @@
-export([
payload_b0/2,
payload_mic/1,
payload_fcnt_low/1
payload_fcnt_low/1,
get_device_for_payload/2
]).

%% biggest unsigned number in 23 bits
Expand Down Expand Up @@ -302,7 +303,7 @@ get_device_for_payload(Payload, PubKeyBin) ->
end;
<<_MType:3, _MHDRRFU:3, _Major:2, DevAddr:4/binary, _/binary>> ->
MIC = payload_mic(Payload),
case find_device(PubKeyBin, DevAddr, MIC, Payload) of
case find_device_for_uplink(PubKeyBin, DevAddr, MIC, Payload) of
{ok, {Device, _NwkSKey, FCnt}} -> {ok, Device, FCnt};
E2 -> E2
end
Expand Down Expand Up @@ -332,10 +333,7 @@ validate_payload_for_device(Device, Payload, PHash, PubKeyBin, Fcnt) ->
{ok, _} ->
case check_device_preferred_hotspots(Device, PubKeyBin) of
none_preferred ->
case maybe_multi_buy_offer(Device, PHash) of
{ok, _} -> ok;
E -> E
end;
ok;
preferred ->
ok;
not_preferred_hotspot ->
Expand Down Expand Up @@ -769,6 +767,13 @@ check_device_is_active(Device, PubKeyBin) ->
Device,
PubKeyBin
),
spawn(fun() ->
DeviceID = router_device:id(Device),
lager:warning("routing for inactive device ~p, removing", [DeviceID]),
ok = router_ics_skf_worker:remove_device_ids([DeviceID]),
ok = router_ics_eui_worker:remove([DeviceID])
end),

{error, ?DEVICE_INACTIVE};
true ->
ok
Expand Down Expand Up @@ -962,22 +967,22 @@ get_device(DevEUI, AppEUI, Msg, MIC) ->
[] ->
{error, api_not_found};
KeysAndDevices ->
find_device(Msg, MIC, KeysAndDevices)
find_device_for_join(Msg, MIC, KeysAndDevices)
end.

-spec find_device(
-spec find_device_for_join(
Msg :: binary(),
MIC :: binary(),
[{binary(), router_device:device()}]
) -> {ok, Device :: router_device:device(), AppKey :: binary()} | {error, not_found}.
find_device(_Msg, _MIC, []) ->
find_device_for_join(_Msg, _MIC, []) ->
{error, not_found};
find_device(Msg, MIC, [{AppKey, Device} | T]) ->
find_device_for_join(Msg, MIC, [{AppKey, Device} | T]) ->
case crypto:macN(cmac, aes_128_cbc, AppKey, Msg, 4) of
MIC ->
{ok, Device, AppKey};
_ ->
find_device(Msg, MIC, T)
find_device_for_join(Msg, MIC, T)
end.

-spec send_to_device_worker(
Expand Down Expand Up @@ -1007,7 +1012,7 @@ send_to_device_worker(
DeviceInfo =
case Device0 of
undefined ->
case find_device(PubKeyBin, DevAddr, MIC, Payload) of
case find_device_for_uplink(PubKeyBin, DevAddr, MIC, Payload) of
{error, unknown_device} ->
lager:warning(
"unable to find device for packet [devaddr: ~p / ~p] [gateway: ~p]",
Expand Down Expand Up @@ -1102,13 +1107,13 @@ send_to_device_worker_(FCnt, Packet, PacketTime, HoldTime, Pid, PubKeyBin, Regio
end
end.

-spec find_device(
-spec find_device_for_uplink(
PubKeyBin :: libp2p_crypto:pubkey_bin(),
DevAddr :: binary(),
MIC :: binary(),
Payload :: binary()
) -> {ok, {router_device:device(), binary(), non_neg_integer()}} | {error, unknown_device}.
find_device(PubKeyBin, DevAddr, MIC, Payload) ->
find_device_for_uplink(PubKeyBin, DevAddr, MIC, Payload) ->
Devices = get_and_sort_devices(DevAddr, PubKeyBin),
case get_device_by_mic(MIC, Payload, Devices) of
undefined ->
Expand Down Expand Up @@ -1185,80 +1190,66 @@ get_and_sort_devices(DevAddr, PubKeyBin) ->
get_device_by_mic(_MIC, _Payload, []) ->
undefined;
get_device_by_mic(ExpectedMIC, Payload, [Device | Devices]) ->
ExpectedFCnt = expected_fcnt(Device, Payload),
B0 = payload_b0(Payload, ExpectedFCnt),
DeviceID = router_device:id(Device),
case router_device:nwk_s_key(Device) of
undefined ->
case router_device:nwk_s_keys(Device) of
[] ->
lager:warning([{device_id, DeviceID}], "device did not have a nwk_s_key, deleting"),
{ok, DB, [_DefaultCF, CF]} = router_db:get(),
ok = router_device:delete(DB, CF, DeviceID),
ok = router_device_cache:delete(DeviceID),
get_device_by_mic(ExpectedMIC, Payload, Devices);
NwkSKey ->
case key_matches_mic(NwkSKey, B0, ExpectedMIC) of
true ->
lager:debug("device ~p NwkSKey matches FCnt ~b.", [DeviceID, ExpectedFCnt]),
{Device, NwkSKey, ExpectedFCnt};
Keys ->
case find_right_key(ExpectedMIC, Payload, Keys) of
false ->
lager:debug(
"device ~p NwkSKey does not match FCnt ~b. Searching device's other keys.",
[DeviceID, ExpectedFCnt]
),
Keys = router_device:keys(Device),
case find_right_key(B0, ExpectedMIC, Payload, Device, Keys) of
false ->
lager:debug("Device does not match FCnt ~b. Searching next device.", [
ExpectedFCnt
]),
get_device_by_mic(ExpectedMIC, Payload, Devices);
{D, K} ->
lager:debug("Device ~p matches FCnt ~b.", [
router_device:id(D), ExpectedFCnt
]),
{D, K, ExpectedFCnt}
end
lager:debug("Device does not match any FCnt. Searching next device."),
get_device_by_mic(ExpectedMIC, Payload, Devices);
{true, NwkSKey, VerifiedFCnt} ->
lager:debug("Device ~p matches FCnt ~b.", [DeviceID, VerifiedFCnt]),
{Device, NwkSKey, VerifiedFCnt}
end
end.

-spec find_right_key(
B0 :: binary(),
MIC :: binary(),
Payload :: binary(),
Device :: router_device:device(),
Keys :: list({binary() | undefined, binary() | undefined})
) -> false | {error, any()} | {router_device:device(), binary()}.
find_right_key(_B0, _MIC, _Payload, _Device, []) ->
Keys :: list(binary())
) -> false | {true, VerifiedNwkSKey :: binary(), VerifiedFCnt :: non_neg_integer()}.
find_right_key(_MIC, _Payload, []) ->
false;
find_right_key(B0, MIC, Payload, Device, [{undefined, _} | Keys]) ->
find_right_key(B0, MIC, Payload, Device, Keys);
find_right_key(B0, MIC, Payload, Device, [{NwkSKey, _} | Keys]) ->
case key_matches_mic(NwkSKey, B0, MIC) of
true ->
{Device, NwkSKey};
false ->
case key_matches_any_fcnt(NwkSKey, MIC, Payload) of
false -> find_right_key(B0, MIC, Payload, Device, Keys);
true -> {Device, NwkSKey}
end
find_right_key(MIC, Payload, [NwkSKey | Keys]) ->
case key_matches_any_fcnt(NwkSKey, MIC, Payload) of
false -> find_right_key(MIC, Payload, Keys);
{true, FCnt} -> {true, NwkSKey, FCnt}
end.

-spec key_matches_any_fcnt(binary(), binary(), binary()) -> boolean().
-spec key_matches_any_fcnt(binary(), binary(), binary()) ->
false | {true, VerifiedFCnt :: non_neg_integer()}.
key_matches_any_fcnt(NwkSKey, ExpectedMIC, Payload) ->
FCntLow = payload_fcnt_low(Payload),
lists:any(
find_first(
fun(HighBits) ->
FCnt = binary:decode_unsigned(
<<FCntLow:16/integer-unsigned-little, HighBits:16/integer-unsigned-little>>,
little
),
B0 = payload_b0(Payload, FCnt),
ComputedMIC = crypto:macN(cmac, aes_128_cbc, NwkSKey, B0, 4),
ComputedMIC =:= ExpectedMIC
{key_matches_mic(NwkSKey, B0, ExpectedMIC), FCnt}
end,
lists:seq(2#000, 2#111)
).

-spec find_first(
Fn :: fun((T) -> {boolean(), T}),
Els :: list(T)
) -> {true, T} | false.
find_first(_Fn, []) ->
false;
find_first(Fn, [Head | Tail]) ->
case Fn(Head) of
{true, _} = Val -> Val;
_ -> find_first(Fn, Tail)
end.

-spec key_matches_mic(binary(), binary(), binary()) -> boolean().
key_matches_mic(Key, B0, ExpectedMIC) ->
ComputedMIC = crypto:macN(cmac, aes_128_cbc, Key, B0, 4),
Expand All @@ -1270,72 +1261,6 @@ payload_fcnt_low(Payload) ->
_/binary>> = Payload,
FCntLow.

-spec expected_fcnt(
Device :: router_device:device(),
Payload :: binary()
) -> non_neg_integer().
expected_fcnt(Device, Payload) ->
%% This is a heuristic for handling replayed packets and one
%% (arguably incorrect) edge case.

%% We need a 32-bit frame counter in order to compute the MIC.

%% The payload contains only the 16 low-order bits of the the frame counter.

%% If the bits from the payload are slightly less than, equal to,
%% or greater than the low order bits of our device's frame
%% counter, then our device's high bits are /probably/ the same as
%% the ones held by the end device. We will join our high bits to
%% the packets's low bits and hope that is the correct FCntUp.

%% On the other hand, if the bits from the payload are
%% significantly less than the low order bits from the device's
%% frame counter, then there's a good chance the end device's low
%% bits have rolled back to zero. In this case, we're going to
%% increment our internal counter's high bits by one and join them
%% to the packet's low bits.

PayloadFCntLow = payload_fcnt_low(Payload),
{PrevFCntLow, PrevFCntHigh, LowDiff} =
case router_device:fcnt(Device) of
undefined ->
{undefined, undefined, undefined};
I when is_integer(I) ->
<<Low:16/integer-unsigned-little, High:16/integer-unsigned-little>> = <<
I:32/integer-unsigned-little
>>,
{Low, High, abs(Low - PayloadFCntLow)}
end,

if
PrevFCntLow =:= undefined andalso LowDiff =:= undefined ->
%% This is the first frame we've seen, so we're going to
%% assume the upper bits of the frame counter are all 0
%% and we'll take the lower bits as-is; this will be the
%% new FCntUp.
PayloadFCntLow;
PayloadFCntLow >= PrevFCntLow ->
%% The FCnt on this packet is gte the last packet, meaning
%% it hasn't rolled back to 0. We're going to prepend the
%% high bits from our internal counter and assume that is
%% the correct FCntUp.
binary:decode_unsigned(<<PrevFCntHigh:16, PayloadFCntLow:16>>);
PayloadFCntLow < PrevFCntLow andalso LowDiff =< 10 ->
%% The FCnt on this packet appears to be slightly lower
%% than our internal counter. We're going to append the
%% upper bits of our internal counter to the packet's
%% lower bits and take that as the new FCntUp.
binary:decode_unsigned(<<PrevFCntHigh:16, PayloadFCntLow:16>>);
PayloadFCntLow < PrevFCntLow andalso LowDiff > 10 ->
%% The FCnt on this packets is significantly less than our
%% internal counter. We're goint to assume the lower 16
%% bits have rolled back to zero. We'll increment the
%% upper bits and append them to the lower bits and take
%% that as the new FCntUp.
NewHigh = (PrevFCntHigh + 1) rem ?MODULO_16_BITS,
binary:decode_unsigned(<<NewHigh:16, PayloadFCntLow:16>>)
end.

-spec payload_b0(binary(), non_neg_integer()) -> binary().
payload_b0(Payload, ExpectedFCnt) ->
<<MType:3, _:5, DevAddr:4/binary, _:4, FOptsLen:4, _:16, _FOpts:FOptsLen/binary, _/binary>> =
Expand Down
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