netdev - Re: [PATCH net] net: dsa: Discard frames from unused ports

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Message-ID: <9421e733-ed1a-0e2e-b587-4f32dad6d8cb@gmail.com>
Date:   Thu, 5 Apr 2018 15:20:14 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>
Subject: Re: [PATCH net] net: dsa: Discard frames from unused ports

On 04/04/2018 07:17 PM, Andrew Lunn wrote:
> On Wed, Apr 04, 2018 at 05:49:10PM -0700, Florian Fainelli wrote:
>> On 04/04/2018 04:56 PM, Andrew Lunn wrote:
>>> The Marvell switches under some conditions will pass a frame to the
>>> host with the port being the CPU port. Such frames are invalid, and
>>> should be dropped. Not dropping them can result in a crash when
>>> incrementing the receive statistics for an invalid port.
>>>
>>> Reported-by: Chris Healy <cphealy@...il.com>
>>> Fixes: 5f6b4e14cada ("net: dsa: User per-cpu 64-bit statistics")
>>
>> Are you sure this is the commit that introduced the problem?
> 
> Hi Florian
> 
> Well, the problem is it crashes when trying to update the
> statistics. The CPU port is not allocated a p->stats64, only slave
> ports get those. So before this patch, there was no crash and the
> frame would be delivered to the master interface. This in itself is
> probably not correct, but also not fatal. Talking to Chris, it seems
> this behaviour has existing for a long while. I needed to use lldpd to
> trigger the issue, because i assume the Marvell switch sees these as
> special frames and forwards them to the CPU. The other thing is, the
> code got refactored recently. So this fix will not rebase to too many
> earlier versions. It needs a fix per tagging protocol for before the
> common dsa_master_find_slave() was added.

Yes what you are explaining makes sense, but does not that mean we would
just be accessing a garbage memory location before as well? It seems to
me like this problem dates back from long before that particular
changeset, and this changeset just made it more obvious. Would that be
accurate?

> 
>>> -	return ds->ports[port].slave;
>>> +	slave_port = &ds->ports[port];
>>> +
>>> +	if (slave_port->type != DSA_PORT_TYPE_USER)
>>
>> Can we optimize this with an unlikely()?
> 
> Yes, that would make sense.
> 
>      Andrew
> 


-- 
Florian