linux-kernel - Re: [PATCH] fbcon: Check font dimension limits

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Date:   Sun, 29 Jan 2023 16:04:33 +0100
From:   Samuel Thibault <samuel.thibault@...-lyon.org>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     gregkh@...uxfoundation.org, Daniel Vetter <daniel@...ll.ch>,
        Helge Deller <deller@....de>, linux-fbdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org,
        Sanan Hasanov <sanan.hasanov@...ghts.ucf.edu>
Subject: Re: [PATCH] fbcon: Check font dimension limits

Jiri Slaby, le jeu. 26 janv. 2023 10:02:55 +0100, a ecrit:
> On 26. 01. 23, 1:49, Samuel Thibault wrote:
> > Index: linux-6.0/drivers/video/fbdev/core/fbcon.c
> > ===================================================================
> > --- 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))))
> 
> So use BIT() properly then? That should be used in all these shifts anyway.
> Exactly to avoid UB.

Right, I'll use that in next version.

Samuel