linux-kernel - Re: [PATCH] fbcon: Fix a NULL pointer dereference issue in fbcon

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <a57734e8-ffb9-4af1-be02-eb0c99507048@gmx.de>
Date: Tue, 17 Sep 2024 08:25:16 +0200
From: Helge Deller <deller@....de>
To: Qianqiang Liu <qianqiang.liu@....com>, aniel@...ll.ch,
 gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Cc: linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 stable@...r.kernel.org, syzbot+3d613ae53c031502687a@...kaller.appspotmail.com
Subject: Re: [PATCH] fbcon: Fix a NULL pointer dereference issue in
 fbcon_putcs

On 9/16/24 03:10, Qianqiang Liu wrote:
> syzbot has found a NULL pointer dereference bug in fbcon [1].
>
> This issue is caused by ops->putcs being a NULL pointer.
> We need to check the pointer before using it.
>
> [1] https://syzkaller.appspot.com/bug?extid=3d613ae53c031502687a
>
> Cc: stable@...r.kernel.org
> Reported-and-tested-by: syzbot+3d613ae53c031502687a@...kaller.appspotmail.com
> Signed-off-by: Qianqiang Liu <qianqiang.liu@....com>
> ---
>   drivers/video/fbdev/core/fbcon.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index 3f7333dca508..96c1262cc981 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -1284,7 +1284,7 @@ static void fbcon_putcs(struct vc_data *vc, const u16 *s, unsigned int count,
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   	struct fbcon_ops *ops = info->fbcon_par;
>
> -	if (!fbcon_is_inactive(vc, info))
> +	if (!fbcon_is_inactive(vc, info) && ops->putcs)

I think this patch just hides the real problem.
How could putcs have become NULL ?

Helge

>   		ops->putcs(vc, info, s, count, real_y(p, ypos), xpos,
>   			   get_color(vc, info, scr_readw(s), 1),
>   			   get_color(vc, info, scr_readw(s), 0));