netdev - Re: [PATCH net-next 2/4] net: mvpp2: add mvpp2_phylink_to

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Message-ID: <20201221104757.2cd8d68c@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 21 Dec 2020 10:47:57 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        stable@...r.kernel.org
Cc:     Marcin Wojtas <mw@...ihalf.com>, Sasha Levin <sashal@...nel.org>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Gabor Samu <samu_gabor@...oo.ca>,
        Jon Nettleton <jon@...id-run.com>,
        Andrew Elwell <andrew.elwell@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH net-next 2/4] net: mvpp2: add mvpp2_phylink_to_port()
 helper

On Mon, 21 Dec 2020 18:30:32 +0000 Russell King - ARM Linux admin wrote:
> On Mon, Dec 21, 2020 at 10:25:39AM -0800, Jakub Kicinski wrote:
> > We need to work with stable maintainers on this, let's see..
> > 
> > Greg asked for a clear description of what happens, from your 
> > previous response it sounds like a null-deref in mvpp2_mac_config(). 
> > Is the netdev -> config -> netdev linking not ready by the time
> > mvpp2_mac_config() is called?  
> 
> We are going round in circles, so nothing is going to happen.
> 
> I stated in detail in one of my emails on the 10th December why the
> problem occurs. So, Greg has the description already. There is no
> need to repeat it.
> 
> Can we please move forward with this?

Well, the fact it wasn't quoted in Marcin's reply and that I didn't
spot it when scanning the 30 email thread should be a clear enough
indication whether pinging threads is a good strategy..

A clear, fresh backport request would had been much more successful 
and easier for Greg to process. If you still don't see a reply in
2 weeks, please just do that.

In case Greg is in fact reading this:

Greg, can we backport: 

6c2b49eb9671 ("net: mvpp2: add mvpp2_phylink_to_port() helper")

to 5.4? Quoting Russell:

The problem is that mvpp2_acpi_start() passes an un-initialised
(zeroed) port->phylink_config, as phylink is not used in ACPI setups.

Crash occurs because port->phylink_config.dev (which is a NULL pointer
in this instance) is passed to to_net_dev():

#define to_net_dev(d) container_of(d, struct net_device, dev)

Which then means netdev_priv(dev) attempts to dereference a not-quite
NULL pointer, leading to an oops.

Folks here are willing to provide a more cut down fix if necessary.

Thanks!