linux-kernel - Re: [PATCH RFC] tty: Fix out-of-bound vmalloc access in imageblit

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Date:   Mon, 31 May 2021 15:18:07 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Igor Matheus Andrade Torrente <igormtorrente@...il.com>
Cc:     jirislaby@...nel.org, linux-kernel@...r.kernel.org,
        syzbot+858dc7a2f7ef07c2c219@...kaller.appspotmail.com
Subject: Re: [PATCH RFC] tty: Fix out-of-bound vmalloc access in imageblit

On Mon, May 31, 2021 at 09:47:13AM -0300, Igor Matheus Andrade Torrente wrote:
> This issue happens when a userspace program does an ioctl
> FBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct
> containing only the fields xres, yres, and bits_per_pixel
> with values.
> 
> If this struct is the same as the previous ioctl, the
> vc_resize() detects it and doesn't call the resize_screen(),
> leaving the fb_var_screeninfo incomplete. And this leads to
> the updatescrollmode() calculates a wrong value to
> fbcon_display->vrows, which makes the real_y() return a
> wrong value of y, and that value, eventually, causes
> the imageblit to access an out-of-bound address value.
> 
> To solve this issue I brougth the resize_screen() the
> beginning of vc_do_resize(), so it will "fix and fill"
> the fb_var_screeninfo even if the screen does not need any
> resizing.
> 
> Reported-and-tested-by: syzbot+858dc7a2f7ef07c2c219@...kaller.appspotmail.com
> Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@...il.com>
> ---
>  drivers/tty/vt/vt.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)

Why is this "RFC"?