linux-kernel - Re: [PATCH] ata: pata_platform: Fix a NULL pointer dereference in __pata_platform

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Message-ID: <851b0f18-a95d-cfd1-54df-a6902f251a4e@opensource.wdc.com>
Date:   Thu, 27 Jan 2022 10:54:08 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Zhou Qingyang <zhou1615@....edu>
Cc:     kjlu@....edu, Alexander Shiyan <shc_work@...l.ru>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Jens Axboe <axboe@...nel.dk>, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ata: pata_platform: Fix a NULL pointer dereference in
 __pata_platform_probe()

On 1/25/22 01:45, Zhou Qingyang wrote:
> In __pata_platform_probe(), devm_kzalloc() is assigned to ap->ops and
> there is a dereference of it right after that, which could introduce a
> NULL pointer dereference bug.
> 
> Fix this by adding a NULL check of ap->ops.
> 
> This bug was found by a static analyzer.
> 
> Builds with 'make allyesconfig' show no new warnings,
> and our static analyzer no longer warns about this code.
> 
> Fixes: f3d5e4f18dba ("ata: pata_of_platform: Allow to use 16-bit wide data transfer")
> Signed-off-by: Zhou Qingyang <zhou1615@....edu>
> ---
> The analysis employs differential checking to identify inconsistent 
> security operations (e.g., checks or kfrees) between two code paths 
> and confirms that the inconsistent operations are not recovered in the
> current function or the callers, so they constitute bugs. 
> 
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.

See below. Reviewing the fix would be good too :)

> 
>  drivers/ata/pata_platform.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/ata/pata_platform.c b/drivers/ata/pata_platform.c
> index 028329428b75..021ef9cbcbc1 100644
> --- a/drivers/ata/pata_platform.c
> +++ b/drivers/ata/pata_platform.c
> @@ -128,6 +128,8 @@ int __pata_platform_probe(struct device *dev, struct resource *io_res,
>  	ap = host->ports[0];
>  
>  	ap->ops = devm_kzalloc(dev, sizeof(*ap->ops), GFP_KERNEL);
> +	if (ap->ops)

This of course should be "if (!ap->ops)", obviously...
I fixed that when applying.

> +		return -ENOMEM;
>  	ap->ops->inherits = &ata_sff_port_ops;
>  	ap->ops->cable_detect = ata_cable_unknown;
>  	ap->ops->set_mode = pata_platform_set_mode;


-- 
Damien Le Moal
Western Digital Research