[PATCH v2 4/4] fbmem: Catch possible driver bugs regarding too small virtual screen size

[Helge Deller]

On 6/25/22 15:03, Daniel Vetter wrote:
> On Sat, Jun 25, 2022 at 02:25:02PM +0200, Helge Deller wrote:
>> Make sure that we catch, report and fix up fbdev and drm graphic drivers which
>> got the virtual screen resolution smaller than the physical screen resolution.
>>
>> Signed-off-by: Helge Deller <deller at gmx.de>
>> Cc: stable at vger.kernel.org # v5.4+
>
> No cc: stable for this, it's not fixing any bugs just helps validate
> driver code.

Ok.

> Also if you just move the check from the ioctl code to here we don't need
> to duplicate anything (and drivers which don't check their set_var are
> kinda busted no matter what).

See previous mail. We need to decide which way we go, then I'll change it.

Thanks!
Helge

> -Daniel
>
>> ---
>>  drivers/video/fbdev/core/fbmem.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
>> index 50fb66b954d6..6d262e341023 100644
>> --- a/drivers/video/fbdev/core/fbmem.c
>> +++ b/drivers/video/fbdev/core/fbmem.c
>> @@ -1006,6 +1006,12 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
>>  	if (var->xres < 8 || var->yres < 8)
>>  		return -EINVAL;
>>
>> +	/* make sure virtual resolution >= physical resolution */
>> +	if (WARN_ON(var->xres_virtual < var->xres))
>> +		var->xres_virtual = var->xres;
>> +	if (WARN_ON(var->yres_virtual < var->yres))
>> +		var->yres_virtual = var->yres;
>> +
>>  	/* Too huge resolution causes multiplication overflow. */
>>  	if (check_mul_overflow(var->xres, var->yres, &unused) ||
>>  	    check_mul_overflow(var->xres_virtual, var->yres_virtual, &unused))
>> --
>> 2.35.3
>>
>