netdev - Re: [PATCH net] can: isotp: isotp_rcv

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Date:   Tue, 18 Jan 2022 15:44:13 +0100
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     "Ziyang Xuan (William)" <william.xuanziyang@...wei.com>,
        mkl@...gutronix.de
Cc:     davem@...emloft.net, kuba@...nel.org, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] can: isotp: isotp_rcv_cf(): fix so->rx race problem

On 18.01.22 13:46, Ziyang Xuan (William) wrote:
>> Hi,
>>
>> the referenced syzbot issue has already been fixed in upstream here:
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=5f33a09e769a9da0482f20a6770a342842443776
>>
>> ("can: isotp: convert struct tpcon::{idx,len} to unsigned int")
>>
>> Additionally this fix changes some behaviour that is required by the ISO 16765-2 specification (see below).
>>
>> On 17.01.22 13:01, Ziyang Xuan wrote:
>>> When receive a FF, the current code logic does not consider the real
>>> so->rx.state but set so->rx.state to ISOTP_IDLE directly. That will
>>> make so->rx accessed by multiple receiving processes concurrently.
>>
>> This is intentionally. "multiple receiving processes" are not allowed resp. specified by ISO 15765-2.
> 
> Does it can be a network attack?

Yes. You can see it like this. The ISO 15765-2 protocol is an unreliable 
UDP-like datagram protocol and the session layer takes care about 
timeouts and packet lost.

If you want to disturb that protocol you can also send PDUs with 
out-of-sync packet counters which will make the receiver drop the 
communication attempt.

This is 'CAN-style' ... as usually the bus is very reliable. Security 
and reliable communication is done on top of these protocols.

> It receives packets from network, but unexpected packets order make server panic.

Haha, no :-)

Unexpected packets should not make the server panic but only drop the 
communication process.

In the case pointed out by syzbot the unsigned 32 bit length information 
was stored in a signed 32 bit integer which caused a sanity check to fail.

This is now fixed with the patch from Marc.

Regards,
Oliver