linux-kernel - Re: [PATCH 07/21] ata: libahci_platform: Sanity check the DT child nodes number

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Message-ID: <ab7f2a2e-0ca9-ed97-e4ed-bf8ef0ed69a5@opensource.wdc.com>
Date:   Thu, 24 Mar 2022 10:40:40 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Hans de Goede <hdegoede@...hat.com>,
        Jens Axboe <axboe@...nel.dk>
Cc:     Serge Semin <fancer.lancer@...il.com>,
        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 07/21] ata: libahci_platform: Sanity check the DT child
 nodes number

On 3/24/22 09:16, 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 4 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>
> ---
>  drivers/ata/libahci_platform.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/ata/libahci_platform.c b/drivers/ata/libahci_platform.c
> index 4fb9629c03ab..845042295b97 100644
> --- a/drivers/ata/libahci_platform.c
> +++ b/drivers/ata/libahci_platform.c
> @@ -470,15 +470,21 @@ struct ahci_host_priv *ahci_platform_get_resources(struct platform_device *pdev,
>  		}
>  	}
>  
> -	hpriv->nports = child_nodes = of_get_child_count(dev->of_node);
> -
>  	/*
> -	 * If no sub-node was found, we still need to set nports to
> -	 * one in order to be able to use the
> +	 * Too many sub-nodes most likely means having something wrong with
> +	 * firmware. 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)
> +	child_nodes = of_get_child_count(dev->of_node);
> +	if (child_nodes > AHCI_MAX_PORTS) {
> +		rc = -EINVAL;
> +		goto err_out;
> +	} else if (!child_nodes) {

No need for "else" after a return.

>  		hpriv->nports = 1;
> +	} else {
> +		hpriv->nports = child_nodes;
> +	}
>  
>  	hpriv->phys = devm_kcalloc(dev, hpriv->nports, sizeof(*hpriv->phys), GFP_KERNEL);
>  	if (!hpriv->phys) {


-- 
Damien Le Moal
Western Digital Research