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From:   "Gix, Brian" <brian.gix@intel.com>
To:     Michal Lowas-Rzechonek <michal.lowas-rzechonek@silvair.com>,
        "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>
Subject: RE: [PATCH BlueZ v3 2/2] mesh: Use current IV Index when relaying
Thread-Topic: [PATCH BlueZ v3 2/2] mesh: Use current IV Index when relaying
Thread-Index: AQHVLLum3Lk9ZQv0r0GsXMB/v28S/qavoLnQ
Date:   Thu, 27 Jun 2019 15:38:17 +0000
Message-ID: <DEBB0CAA2616974FAE35E4B560B9A4376CBB1464@ORSMSX103.amr.corp.intel.com>
References: <20190627074043.22891-1-michal.lowas-rzechonek@silvair.com>
 <20190627074043.22891-3-michal.lowas-rzechonek@silvair.com>
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Hi Michal,

> -----Original Message-----
> From: linux-bluetooth-owner@vger.kernel.org [mailto:linux-bluetooth-
> owner@vger.kernel.org] On Behalf Of Michal Lowas-Rzechonek
> Sent: Thursday, June 27, 2019 12:41 AM
> To: linux-bluetooth@vger.kernel.org
> Cc: Gix, Brian <brian.gix@intel.com>
> Subject: [PATCH BlueZ v3 2/2] mesh: Use current IV Index when relaying
> 
> If we are in IV Update state, packets shall be transmitted using IV Index - 1,
> including relayed packets.
> ---
>  mesh/net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mesh/net.c b/mesh/net.c
> index a5693f154..0a6ff8eac 100644
> --- a/mesh/net.c
> +++ b/mesh/net.c
> @@ -2512,7 +2512,7 @@ static void net_rx(void *net_ptr, void *user_data)
>  	relay_advice = packet_received(net, key_id, iv_index,
>  							out, out_size, rssi);
>  	if (relay_advice > data->relay_advice) {
> -		data->iv_index = iv_index;
> +		data->iv_index = mesh_net_get_iv_index(net);

I don't think this is correct.  *relayed* packets must preserve the originators IV_Index...

At most, two different IV_Index values are considered valid at any time in the mesh.  Each node has it's own sense as to what the *Network* IV_Index is, and it shall accept that IV_Index, and 1 less...  With this difference reflected in the IVI bit of the first octet.

When acting as a relay, incoming messages must be one of these two settings to be recognized, but after decrementing TTL and re-encrypting, the IV_Index of the original sender must be preserved.  The iv_index is part of both the Network nonce and the Access layer nonce.  If a relay uses a different nonce than the originator (SRC), then the receiving DST device will be unable to decrypt the Access layer using the same nonce as the repackaged Network layer.


>  		data->relay_advice = relay_advice;
>  		data->key_id = key_id;
>  		data->net = net;
> --
> 2.19.1