linux-kernel - Re: [PATCH] media: rc: fix check on dev->min_timeout for LIRC_GET_MIN

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Message-ID: <20200915171256.GA681@gofer.mess.org>
Date:   Tue, 15 Sep 2020 18:12:56 +0100
From:   Sean Young <sean@...s.org>
To:     Colin King <colin.king@...onical.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Maxim Levitsky <maximlevitsky@...il.com>,
        linux-media@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: rc: fix check on dev->min_timeout for
 LIRC_GET_MIN_TIMEOUT ioctl

On Tue, Sep 15, 2020 at 04:36:08PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently the LIRC_GET_MIN_TIMEOUT is checking for a null dev->max_timeout
> and then accessing dev->min_timeout, hence we may have a potential null
> pointer dereference issue.  This looks like a cut-n-paste typo, fix it
> by checking on dev->min_timeout before accessing it.

max_timeout and min_timeout are both u32, not pointers. So, the commit 
message is wrong: there is no null pointer dereference issue.

Every driver which has max_timeout also has min_timeout set (I've checked
for this). So technically this is not wrong, but maybe it looks wrong?

Thanks,

Sean
> 
> Addresses-Coverity: ("Copy-paste error")
> Fixes: e589333f346b ("V4L/DVB: IR: extend interfaces to support more device settings")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/media/rc/lirc_dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/rc/lirc_dev.c b/drivers/media/rc/lirc_dev.c
> index 220363b9a868..d230c21e1d31 100644
> --- a/drivers/media/rc/lirc_dev.c
> +++ b/drivers/media/rc/lirc_dev.c
> @@ -533,7 +533,7 @@ static long lirc_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>  
>  	/* Generic timeout support */
>  	case LIRC_GET_MIN_TIMEOUT:
> -		if (!dev->max_timeout)
> +		if (!dev->min_timeout)
>  			ret = -ENOTTY;
>  		else
>  			val = dev->min_timeout;
> -- 
> 2.27.0