[PATCH] fbcon: Check font dimension limits

[Jiri Slaby]

On 26. 01. 23, 8:43, Greg KH wrote:
>> --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
>> +++ linux-6.0/drivers/video/fbdev/core/fbcon.c
>> @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
>>   	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
>>   		return -EINVAL;
>>   
>> +	if (font->width > 32 || font->height > 32)
>> +		return -EINVAL;
>> +
>>   	/* Make sure drawing engine can handle the font */
>> -	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
>> -	    !(info->pixmap.blit_y & (1 << (font->height - 1))))
>> +	if (!(info->pixmap.blit_x & (1U << (font->width - 1))) ||
>> +	    !(info->pixmap.blit_y & (1U << (font->height - 1))))
> 
> Are you sure this is still needed with the above check added?  If so,
> why?  What is the difference in the compiled code?

For font->{width,height} == 32, definitely. IMO, 1 << 31 is undefined as 
1 << 31 cannot be represented by an (signed) int.

-- 
js
suse labs