Date:   Sun, 29 Jan 2023 16:04:33 +0100
From:   Samuel Thibault <samuel.thibault@ens-lyon.org>
To:     Jiri Slaby <jirislaby@kernel.org>
Cc:     gregkh@linuxfoundation.org, Daniel Vetter <daniel@ffwll.ch>,
        Helge Deller <deller@gmx.de>, linux-fbdev@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org,
        Sanan Hasanov <sanan.hasanov@Knights.ucf.edu>
Subject: Re: [PATCH] fbcon: Check font dimension limits
Message-ID: <20230129150433.gmdmger2ah63nsg7@begin>
Mail-Followup-To: Samuel Thibault <samuel.thibault@ens-lyon.org>,
        Jiri Slaby <jirislaby@kernel.org>, gregkh@linuxfoundation.org,
        Daniel Vetter <daniel@ffwll.ch>, Helge Deller <deller@gmx.de>,
        linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Sanan Hasanov <sanan.hasanov@Knights.ucf.edu>
References: <20230126004911.869923511@ens-lyon.org>
 <20230126004921.616264824@ens-lyon.org>
 <3bcd9911-5fdd-2a1a-0a76-55e1b8f7642a@kernel.org>
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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