linux-kernel - Re: KMSAN: uninit-value in can

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Date:   Wed, 20 Nov 2019 21:10:24 +0100
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        syzbot <syzbot+b02ff0707a97e4e79ebb@...kaller.appspotmail.com>,
        davem@...emloft.net, glider@...gle.com, linux-can@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: KMSAN: uninit-value in can_receive

On 19/11/2019 22.09, Eric Dumazet wrote:
> On 11/19/19 12:24 PM, Oliver Hartkopp wrote:
>> Please check commit d3b58c47d330d ("can: replace timestamp as unique skb attribute").
> 
> Oh well... This notion of 'unique skb attribute' is interesting...

Yes. The problem is that the joined filter needs to detect the identical 
skb which is delivered several times to raw_rcv() to process filters 
that are logical ANDed.

>> can_skb_prv(skb)->skbcnt is set to 0 at skb creation time when sending CAN frames from local host or receiving CAN frames from a real CAN interface.
> 
> We can not enforce this to happen with a virtual interface.

You are right. I just discovered that I'm not able to send CAN frames 
via PF_PACKET sockets anymore.

Receiving with a simple test program and Wireshark is fine - but sending 
does not work. PF_PACKET is not creating the same kind of skbs as e.g. 
the CAN_RAW socket does.

So the KMSAN detection was right at the end :-(

I'll take a closer look to enable PF_PACKET to send CAN frames again 
which will fix up the entire  problem.

Thanks for your feedback!

Best,
Oliver