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Subject: Re: [PATCH net 2/3] can: j1939: j1939_can_recv(): ignore messages
 with invalid source address
To:     Oleksij Rempel <o.rempel@pengutronix.de>
CC:     Robin van der Gracht <robin@protonic.nl>,
        Oleksij Rempel <linux@rempel-privat.de>,
        <kernel@pengutronix.de>, Oliver Hartkopp <socketcan@hartkopp.net>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-can@vger.kernel.org>
References: <1634825057-47915-1-git-send-email-zhangchangzhong@huawei.com>
 <1634825057-47915-3-git-send-email-zhangchangzhong@huawei.com>
 <20211022102306.GB20681@pengutronix.de>
From:   Zhang Changzhong <zhangchangzhong@huawei.com>
Message-ID: <9c636d7f-70df-18c9-66ed-46eb21f4ffbb@huawei.com>
Date:   Mon, 25 Oct 2021 15:30:57 +0800
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On 2021/10/22 18:23, Oleksij Rempel wrote:
> On Thu, Oct 21, 2021 at 10:04:16PM +0800, Zhang Changzhong wrote:
>> According to SAE-J1939-82 2015 (A.3.6 Row 2), a receiver should never
>> send TP.CM_CTS to the global address, so we can add a check in
>> j1939_can_recv() to drop messages with invalid source address.
>>
>> Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
>> Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
> 
> NACK. This will break Address Claiming, where first message is SA == 0xff

I know that 0xfe can be used as a source address, but which message has a source
address of 0xff?

According to SAE-J1939-81 2017 4.2.2.8：

  The network address 255, also known as the Global address, is permitted in the
  Destination Address field of the SAE J1939 message identifier but never in the
  Source Address field.

> 
>> ---
>>  net/can/j1939/main.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/net/can/j1939/main.c b/net/can/j1939/main.c
>> index 08c8606..4f1e4bb 100644
>> --- a/net/can/j1939/main.c
>> +++ b/net/can/j1939/main.c
>> @@ -75,6 +75,10 @@ static void j1939_can_recv(struct sk_buff *iskb, void *data)
>>  	skcb->addr.pgn = (cf->can_id >> 8) & J1939_PGN_MAX;
>>  	/* set default message type */
>>  	skcb->addr.type = J1939_TP;
>> +	if (!j1939_address_is_valid(skcb->addr.sa))
>> +		/* ignore messages whose sa is broadcast address */
>> +		goto done;
>> +
>>  	if (j1939_pgn_is_pdu1(skcb->addr.pgn)) {
>>  		/* Type 1: with destination address */
>>  		skcb->addr.da = skcb->addr.pgn;
>> -- 
>> 2.9.5
>>
>>
>>
>