From: Greg KH <gregkh@linuxfoundation.org>
To: Igor Matheus Andrade Torrente <igormtorrente@gmail.com>
Cc: jirislaby@kernel.org, linux-kernel@vger.kernel.org,
syzbot+858dc7a2f7ef07c2c219@syzkaller.appspotmail.com
Subject: Re: [PATCH v3] tty: Fix out-of-bound vmalloc access in imageblit
Date: Thu, 24 Jun 2021 14:57:39 +0200 [thread overview]
Message-ID: <YNSBQxVidmlZz5YM@kroah.com> (raw)
In-Reply-To: <20210617223720.29378-1-igormtorrente@gmail.com>
On Thu, Jun 17, 2021 at 07:37:20PM -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 made the resize_screen() be called
> even if the screen does not need any resizing, so it will
> "fix and fill" the fb_var_screeninfo independently.
>
> Reported-and-tested-by: syzbot+858dc7a2f7ef07c2c219@syzkaller.appspotmail.com
> Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@gmail.com>
> ---
> v2: It Tries to avoid the problem found by Greg in the previous
> patch.
>
> v3: Add a big comment explaining why this is being done the way
> it is.
> ---
> drivers/tty/vt/vt.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index fa1548d4f94b..a0207525a945 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -1220,7 +1220,20 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
> new_screen_size = new_row_size * new_rows;
>
> if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
> - return 0;
> + /* This function is being called here to cover the case
Please do not use networking style comments, use normal ones:
/*
* This function...
> + * where the userspace calls the FBIOPUT_VSCREENINFO twice,
> + * passing the same fb_var_screeninfo containing only the
> + * fields xres, yres, and bits_per_pixel with yeird(but valid)
"yeird"?
And put a space after that word please.
thanks,
greg k-h
prev parent reply other threads:[~2021-06-24 12:57 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-17 22:37 [PATCH v3] tty: Fix out-of-bound vmalloc access in imageblit Igor Matheus Andrade Torrente
2021-06-24 12:57 ` Greg KH [this message]
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