Re: [PATCH v2] UBSAN: shift-out-of-bounds in set_flicker

From: Greg KH <greg@kroah.com>
To: coolrrsh@gmail.com
Cc: slark_xiao@163.com, linux-kernel@vger.kernel.org,
	syzbot+e27f3dbdab04e43b9f73@syzkaller.appspotmail.com,
	mchehab@kernel.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	linux-media@vger.kernel.org
Subject: Re: [PATCH v2] UBSAN: shift-out-of-bounds in set_flicker
Date: Thu, 24 Aug 2023 09:13:54 +0200	[thread overview]
Message-ID: <2023082425-argue-tartar-4652@gregkh> (raw)
In-Reply-To: <20230824070630.8209-1-coolrrsh@gmail.com>

On Thu, Aug 24, 2023 at 12:36:30PM +0530, coolrrsh@gmail.com wrote:
> From: Rajeshwar R Shinde <coolrrsh@gmail.com>
> 
> Syzkaller reported the following issue:
> 
> UBSAN: shift-out-of-bounds in drivers/media/usb/gspca/cpia1.c:1031:27
> shift exponent 245 is too large for 32-bit type 'int'
> 
> shift-out-of-bounds error was triggered when variable 
> 'sd->params.exposure.gain' is greater than the number of bits of int.
> When the variable 'currentexp' is left shifted beyond 31 bits then
> the error is produced. Therefore added the conditional expression to 
> verify valid range.
> 
> Tested via syzbot.
> 
> Reported-by: syzbot+e27f3dbdab04e43b9f73@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/20230818164522.12806-1-coolrrsh@gmail.com
> 
> Link: https://syzkaller.appspot.com/bug?extid=e27f3dbdab04e43b9f73
> 
> Signed-off-by: Rajeshwar R Shinde <coolrrsh@gmail.com>

Please do not have blank lines beween these tags.

You also have trailing whitespace in your changelog text :(

> ---
> v1->v2
> changed the patch
> changed commit message and tested with checkpatch 
> 
> ---
>  drivers/media/usb/gspca/cpia1.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/media/usb/gspca/cpia1.c b/drivers/media/usb/gspca/cpia1.c
> index 46ed95483e22..dafc522d5e7b 100644
> --- a/drivers/media/usb/gspca/cpia1.c
> +++ b/drivers/media/usb/gspca/cpia1.c
> @@ -1028,6 +1028,8 @@ static int set_flicker(struct gspca_dev *gspca_dev, int on, int apply)
>  			sd->params.exposure.expMode = 2;
>  			sd->exposure_status = EXPOSURE_NORMAL;
>  		}
> +		if (sd->params.exposure.gain > 31)
> +			return -1;

Do not make up error codes, please return a valid one and not a random
negative number.  Unless -1 is a valid value for this function?

thanks,

greg k-h
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