Re: [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.

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