linux-kernel - Re: [PATCH] fbdev: Detect integer underflow at "struct fbcon_ops"->clear

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Message-ID: <a2433659-4f95-d508-11de-8273fd2b6632@i-love.sakura.ne.jp>
Date:   Wed, 15 Jul 2020 09:24:06 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     George Kennedy <george.kennedy@...cle.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-fbdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] fbdev: Detect integer underflow at "struct
 fbcon_ops"->clear_margins.

On 2020/07/15 2:15, George Kennedy wrote:
> Can you try the a.out built from the original Syzkaller modified repro C program? It walks 0-7 through xres and yres of the fb_var_screeninfo struct.

I'm not familiar with exploit code. What do you want to explain via this program?

>   struct fb_var_screeninfo *varp = (struct fb_var_screeninfo *)0x200001c0;
>   struct fb_var_screeninfo *starting_varp = malloc(sizeof(struct fb_var_screeninfo *));

>     memcpy(starting_varp, varp, sizeof(struct fb_var_screeninfo));

>             memcpy(varp, starting_varp, sizeof(struct fb_var_screeninfo));

At least, I suspect there is a memory corruption bug in this program
because of malloc()ing only sizeof(struct fb_var_screeninfo *) bytes.