linux-kernel - Re: [PATCH v4 08/23] ata: libahci_platform: Sanity check the DT child nodes number

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Date:   Wed, 15 Jun 2022 23:53:28 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Hans de Goede <hdegoede@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.de>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Rob Herring <robh+dt@...nel.org>, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 08/23] ata: libahci_platform: Sanity check the DT
 child nodes number

On Tue, Jun 14, 2022 at 05:23:33PM +0900, Damien Le Moal wrote:
> On 6/10/22 17:17, Serge Semin wrote:
> > Having greater than AHCI_MAX_PORTS (32) ports detected isn't that critical
> > from the further AHCI-platform initialization point of view since
> > exceeding the ports upper limit will cause allocating more resources than
> > will be used afterwards. But detecting too many child DT-nodes doesn't
> > seem right since it's very unlikely to have it on an ordinary platform. In
> > accordance with the AHCI specification there can't be more than 32 ports
> > implemented at least due to having the CAP.NP field of 5 bits wide and the
> > PI register of dword size. Thus if such situation is found the DTB must
> > have been corrupted and the data read from it shouldn't be reliable. Let's
> > consider that as an erroneous situation and halt further resources
> > allocation.
> > 
> > Note it's logically more correct to have the nports set only after the
> > initialization value is checked for being sane. So while at it let's make
> > sure nports is assigned with a correct value.
> > 
> > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > Reviewed-by: Hannes Reinecke <hare@...e.de>
> > 
> > ---
> > 
> > Changelog v2:
> > - Drop the else word from the child_nodes value checking if-else-if
> >   statement (@Damien) and convert the after-else part into the ternary
> >   operator-based statement.
> > 
> > Changelog v4:
> > - Fix some logical mistakes in the patch log. (@Sergei Shtylyov)
> > ---
> >  drivers/ata/libahci_platform.c | 13 ++++++++++---
> >  1 file changed, 10 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/ata/libahci_platform.c b/drivers/ata/libahci_platform.c
> > index 814804582d1d..8aed7b29c7ab 100644
> > --- a/drivers/ata/libahci_platform.c
> > +++ b/drivers/ata/libahci_platform.c
> > @@ -451,15 +451,22 @@ struct ahci_host_priv *ahci_platform_get_resources(struct platform_device *pdev,
> >  		}
> >  	}
> >  
> > -	hpriv->nports = child_nodes = of_get_child_count(dev->of_node);
> > +	/*
> > +	 * Too many sub-nodes most likely means having something wrong with
> > +	 * the firmware.
> > +	 */
> > +	child_nodes = of_get_child_count(dev->of_node);
> > +	if (child_nodes > AHCI_MAX_PORTS) {
> > +		rc = -EINVAL;
> > +		goto err_out;
> > +	}
> >  
> >  	/*
> >  	 * If no sub-node was found, we still need to set nports to
> >  	 * one in order to be able to use the
> >  	 * ahci_platform_[en|dis]able_[phys|regulators] functions.
> >  	 */
> > -	if (!child_nodes)
> > -		hpriv->nports = 1;
> > +	hpriv->nports = child_nodes ?: 1;
> 

> This change is not necessary and makes the code far less easy to read.

elaborate please. What change? What part of this change makes the code
less easy to read?

-Sergey

> 
> >  
> >  	hpriv->phys = devm_kcalloc(dev, hpriv->nports, sizeof(*hpriv->phys), GFP_KERNEL);
> >  	if (!hpriv->phys) {
> 
> 
> -- 
> Damien Le Moal
> Western Digital Research