netdev - Re: [PATCH 1/6] property: add fwnode_property_read_string

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Message-ID: <YjhUHjeqL2UpB0Gm@smile.fi.intel.com>
Date:   Mon, 21 Mar 2022 12:31:58 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Clément Léger <clement.leger@...tlin.com>
Cc:     Daniel Scally <djrscally@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "'Rafael J . Wysocki '" <rafael@...nel.org>,
        Wolfram Sang <wsa@...nel.org>, Peter Rosin <peda@...ntia.se>,
        Russell King <linux@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Allan Nielsen <allan.nielsen@...rochip.com>,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-i2c@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 1/6] property: add fwnode_property_read_string_index()

On Mon, Mar 21, 2022 at 08:49:21AM +0100, Clément Léger wrote:
> Le Fri, 18 Mar 2022 20:09:37 +0200,
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> a écrit :
> > On Fri, Mar 18, 2022 at 05:49:12PM +0100, Clément Léger wrote:
> > > Le Fri, 18 Mar 2022 18:26:00 +0200,
> > > Andy Shevchenko <andriy.shevchenko@...ux.intel.com> a écrit :  
> > > > On Fri, Mar 18, 2022 at 05:00:47PM +0100, Clément Léger wrote:  

...

> > > > > +	values = kcalloc(nval, sizeof(*values), GFP_KERNEL);
> > > > > +	if (!values)
> > > > > +		return -ENOMEM;
> > > > > +
> > > > > +	ret = fwnode_property_read_string_array(fwnode, propname, values, nval);
> > > > > +	if (ret < 0)
> > > > > +		goto out;
> > > > > +
> > > > > +	*string = values[index];
> > > > > +out:
> > > > > +	kfree(values);    
> > > > 
> > > > Here is UAF (use after free). How is it supposed to work?  
> > > 
> > > values is an array of pointers. I'm only retrieving a pointer out of
> > > it.  
> > 
> > I see, thanks for pointing out.
> > 
> > Nevertheless, I don't like the idea of allocating memory in this case.
> > Can we rather add a new callback that will provide us the necessary
> > property directly?
> > 
> 
> IMHO, it would indeed be better. However,
> fwnode_property_match_string() also allocates memory to do the same
> kind of operation. Would you also like a callback for this one ?

But matching string will need all of them to cover all possible cases.
So, it doesn't rely on the certain index and needs allocation anyway.

-- 
With Best Regards,
Andy Shevchenko