[PATCH] fbdev: tgafb: Fix potential divide by zero

[PATCH] fbdev: tgafb: Fix potential divide by zero

[harperchen]

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@gmail.com>
---
 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;
-- 
2.25.1

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

[Helge Deller]

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@gmail.com>

Could you provide a real name?
Otherwise applied to fbdev git tree.

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;

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

[Wei Chen]

Dear Helge,

Thank you for the kind words. My real name is Wei Chen.

Please apply this patch to fbdev git tree if it is correct.

Best,
Wei

On Thu, 9 Mar 2023 at 06:05, Helge Deller <deller@gmx.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@gmail.com>
>
> Could you provide a real name?
> Otherwise applied to fbdev git tree.
>
> 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;
>

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

[Jani Nikula]

On Wed, 08 Mar 2023, Helge Deller <deller@gmx.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@gmail.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

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

[Helge Deller]

On 3/9/23 08:53, Jani Nikula wrote:
> On Wed, 08 Mar 2023, Helge Deller <deller@gmx.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@gmail.com>
>>
>> Could you provide a real name?
>> Otherwise applied to fbdev git tree.
>
> See commit d4563201f33a ("Documentation: simplify and clarify DCO
> contribution example language").

Nice. Thanks for that link!
Btw, I did applied that patch yesterday to my tree with just the nickname,
but of course I do prefer real names which is why I asked.

Helge