Message-ID: <727b87ec3e93c6cfd9524d3947ca6e272cdf1a38.camel@gmail.com>
Subject: Re: [PATCHv2] fbcon: Check font dimension limits
From:   Miko Larsson <mikoxyzzz@gmail.com>
To:     Samuel Thibault <samuel.thibault@ens-lyon.org>,
        gregkh@linuxfoundation.org, Daniel Vetter <daniel@ffwll.ch>,
        Helge Deller <deller@gmx.de>
Cc:     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>
Date:   Sun, 29 Jan 2023 18:09:03 +0100
In-Reply-To: <20230129151740.x5p7jj2pbuilpzzt@begin>
References: <20230129151740.x5p7jj2pbuilpzzt@begin>
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On Sun, 2023-01-29 at 16:17 +0100, Samuel Thibault wrote:
> blit_x and blit_y are u32, so fbcon currently cannot support fonts
> larger than 32x32.
>=20
> The 32x32 case also needs shifting an unsigned int, to properly set
> bit
> 31, otherwise we get "UBSAN: shift-out-of-bounds in fbcon_set_font",
> as reported on:
>=20
> http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07=
MB9830.namprd07.prod.outlook.com
> Kernel Branch: 6.2.0-rc5-next-20230124
> Kernel config:
> https://drive.google.com/file/d/1F-LszDAizEEH0ZX0HcSR06v5q8FPl2Uv/view?us=
p=3Dsharing
> Reproducer:
> https://drive.google.com/file/d/1mP1jcLBY7vWCNM60OMf-ogw-urQRjNrm/view?us=
p=3Dsharing
>=20
> Reported-by: Sanan Hasanov <sanan.hasanov@Knights.ucf.edu>
> Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
> Fixes: 2d2699d98492 ("fbcon: font setting should check limitation of
> driver")
> Cc: stable@vger.kernel.org
>=20
> ---
> v1 -> v2:
> - Use BIT macro instead of fixing bit test by hand.
> - Add Fixes and Cc: stable headers.
>=20
> Index: linux-6.0/drivers/video/fbdev/core/fbcon.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- 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
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 h > FB=
CON_SWAP(info->var.rotate, info->var.yres, info-
> >var.xres))
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0return -EINVAL;
> =C2=A0
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (font->width > 32 || font->=
height > 32)
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0return -EINVAL;
> +
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0/* Make sure drawing engi=
ne can handle the font */
> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (!(info->pixmap.blit_x & (1=
 << (font->width - 1))) ||
> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 !(info->pix=
map.blit_y & (1 << (font->height - 1))))
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (!(info->pixmap.blit_x & BI=
T(font->width - 1)) ||
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 !(info->pix=
map.blit_y & BIT(font->height - 1)))
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0return -EINVAL;
> =C2=A0
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0/* Make sure driver can h=
andle the font length */

Tested-by: Miko Larsson <mikoxyzzz@gmail.com>
--=20
~miko