linux-kernel - Re: [PATCH] fbdev: tgafb: Fix potential divide by zero

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Date:   Thu, 09 Mar 2023 09:53:56 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Helge Deller <deller@....de>, harperchen <harperchen1110@...il.com>
Cc:     linux-fbdev@...r.kernel.org, javierm@...hat.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        wsa+renesas@...g-engineering.com, tzimmermann@...e.de
Subject: Re: [PATCH] fbdev: tgafb: Fix potential divide by zero

On Wed, 08 Mar 2023, Helge Deller <deller@....de> wrote:
> On 3/7/23 14:08, harperchen wrote:
>> fb_set_var would by called when user invokes ioctl with cmd
>> FBIOPUT_VSCREENINFO. User-provided data would finally reach
>> tgafb_check_var. In case var->pixclock is assigned to zero,
>> divide by zero would occur when checking whether reciprocal
>> of var->pixclock is too high.
>>
>> Similar crashes have happened in other fbdev drivers. There
>> is no check and modification on var->pixclock along the call
>> chain to tgafb_check_var. We believe it could also be triggered
>> in driver tgafb from user site.
>>
>> Signed-off-by: harperchen <harperchen1110@...il.com>
>
> Could you provide a real name?
> Otherwise applied to fbdev git tree.

See commit d4563201f33a ("Documentation: simplify and clarify DCO
contribution example language").

BR,
Jani.


>
> Thanks!
> Helge
>
>> ---
>>   drivers/video/fbdev/tgafb.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/video/fbdev/tgafb.c b/drivers/video/fbdev/tgafb.c
>> index 14d37c49633c..b44004880f0d 100644
>> --- a/drivers/video/fbdev/tgafb.c
>> +++ b/drivers/video/fbdev/tgafb.c
>> @@ -173,6 +173,9 @@ tgafb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
>>   {
>>   	struct tga_par *par = (struct tga_par *)info->par;
>>
>> +	if (!var->pixclock)
>> +		return -EINVAL;
>> +
>>   	if (par->tga_type == TGA_TYPE_8PLANE) {
>>   		if (var->bits_per_pixel != 8)
>>   			return -EINVAL;
>

-- 
Jani Nikula, Intel Open Source Graphics Center