linux-kernel - Re: [PATCH 1/2] i2c-dev: don't get i2c adapter via i2c

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Date:	Thu, 7 Jul 2016 15:16:54 +0200
From:	Jean Delvare <jdelvare@...e.de>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Wolfram Sang <wsa@...-dreams.de>, Jean Delvare <jdelvare@...e.com>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, Johan Hovold <johan@...nel.org>,
	Alex Elder <elder@...aro.org>
Subject: Re: [PATCH 1/2] i2c-dev: don't get i2c adapter via i2c_dev

On Tue,  5 Jul 2016 19:57:06 -0700, Viresh Kumar wrote:
> There is no code protecting i2c_dev to be freed after it is returned
> from i2c_dev_get_by_minor() and using it to access the value which we
> already have (minor) isn't safe really.
> 
> Avoid using it and get the adapter directly from 'minor'.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/i2c/i2c-dev.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
> index 6ecfd76270f2..66f323fd3982 100644
> --- a/drivers/i2c/i2c-dev.c
> +++ b/drivers/i2c/i2c-dev.c
> @@ -485,13 +485,8 @@ static int i2cdev_open(struct inode *inode, struct file *file)
>  	unsigned int minor = iminor(inode);
>  	struct i2c_client *client;
>  	struct i2c_adapter *adap;
> -	struct i2c_dev *i2c_dev;
> -
> -	i2c_dev = i2c_dev_get_by_minor(minor);
> -	if (!i2c_dev)
> -		return -ENODEV;
>  
> -	adap = i2c_get_adapter(i2c_dev->adap->nr);
> +	adap = i2c_get_adapter(minor);
>  	if (!adap)
>  		return -ENODEV;
>  

Anyway, this is a good cleanup/optimization on its own, on top of
fixing a race condition, independently of what we decide for the rest
of the problems being discussed in this thread. So:

Reviewed-by: Jean Delvare <jdelvare@...e.de>
Tested-by: Jean Delvare <jdelvare@...e.de>

Thanks,
-- 
Jean Delvare
SUSE L3 Support