linux-kernel - Re: [PATCH v2 2/8] phy: mvebu-cp110-comphy: fix port check in ->xlate()

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Date:   Mon, 3 Dec 2018 14:56:22 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Gregory Clement <gregory.clement@...tlin.com>,
        Jason Cooper <jason@...edaemon.net>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Grzegorz Jaszczyk <jaz@...ihalf.com>,
        linux-kernel@...r.kernel.org,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Nadav Haklai <nadavh@...vell.com>,
        Rob Herring <robh+dt@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/8] phy: mvebu-cp110-comphy: fix port check in
 ->xlate()

Hi Russell,

Russell King - ARM Linux <linux@...linux.org.uk> wrote on Mon, 3 Dec
2018 00:36:23 +0000:

> On Sun, Dec 02, 2018 at 08:35:09PM +0100, Miquel Raynal wrote:
> > Hi Russell,
> > 
> > Russell King - ARM Linux <linux@...linux.org.uk> wrote on Fri, 30 Nov
> > 2018 19:00:31 +0000:
> >   
> > > On Fri, Nov 30, 2018 at 03:47:37PM +0100, Miquel Raynal wrote:  
> > > > So far the PHY ->xlate() callback was checking if the port was
> > > > "invalid" before continuing, meaning that the port has not been used
> > > > yet. This check is not correct as there is no opposite call to    
> > > > ->xlate() once the PHY is released by the user and the port will    
> > > > remain "valid" after the first phy_get()/phy_put() calls. Hence, if
> > > > this driver is built as a module, inserted, removed and inserted
> > > > again, the PHY will appear busy and the second probe will fail.
> > > > 
> > > > To fix this, just drop the faulty check and instead verify that the
> > > > port number is valid (ie. in the possible range).
> > > > 
> > > > Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> > > > ---
> > > >  drivers/phy/marvell/phy-mvebu-cp110-comphy.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/phy/marvell/phy-mvebu-cp110-comphy.c b/drivers/phy/marvell/phy-mvebu-cp110-comphy.c
> > > > index 31b9a1c18345..a40b876ff214 100644
> > > > --- a/drivers/phy/marvell/phy-mvebu-cp110-comphy.c
> > > > +++ b/drivers/phy/marvell/phy-mvebu-cp110-comphy.c
> > > > @@ -567,9 +567,9 @@ static struct phy *mvebu_comphy_xlate(struct device *dev,
> > > >  		return phy;
> > > >  
> > > >  	lane = phy_get_drvdata(phy);
> > > > -	if (lane->port >= 0)
> > > > -		return ERR_PTR(-EBUSY);
> > > >  	lane->port = args->args[0];
> > > > +	if (lane->port >= MVEBU_COMPHY_PORTS)
> > > > +		return ERR_PTR(-EINVAL);    
> > > 
> > > Shouldn't we validate args->args[0] before doing anything?
> > >   
> > 
> > I don't understand your point, there is a check on args->args[0] as
> > we check its value (through lane->port) right after. What do you
> > have in mind?  
> 
> Right, there is already a check on args->args[0] for it being greater
> than MVEBU_COMPHY_PORTS and returning an error (and in fact warning
> if that is the case).  So in that case, what is the use of the above
> additional test you are proposing to add?  The resulting code ends up
> looking like this:
> 
> 	if (WARN_ON(args->args[0] >= MVEBU_COMPHY_PORTS))
> 		return ERR_PTR(-EINVAL);
> ...
> 	lane->port = args->args[0];
> +	if (lane->port >= MVEBU_COMPHY_PORTS)
> +		return ERR_PTR(-EINVAL);  
> 
> which is just silly - the second test can never be evaluated as true,
> and therefore is redundant.
> 
> In any case, my point was that in your patch, where you assign
> lane->port and then validate the lane->port value, this is in
> principle the wrong order - the order should always be: validate
> first, then make use.
> 

You are right, this test is redundant; I forgot about the first
check. I will just drop these additional two lines and just do:

                [...]
                lane->port = args->args[0];

                return 0;
        }

Thanks,
Miquèl