linux-kernel - Re: [PATCH] vt: Clear selection before changing the font

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Message-ID: <166886f8-eb9e-f779-cf57-1ea353adc446@gmail.com>
Date:   Sun, 31 Jul 2022 17:32:41 +0600
From:   Khalid Masum <khalid.masum.92@...il.com>
To:     Helge Deller <deller@....de>,
        syzbot <syzbot+14b0e8f3fd1612e35350@...kaller.appspotmail.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Subject: Re: [PATCH] vt: Clear selection before changing the font

On 7/31/22 00:50, Helge Deller wrote:
> When changing the console font with ioctl(KDFONTOP) the new font size
> can be bigger than the previous font. A previous selection may thus now
> be outside of the new screen size and thus trigger out-of-bounds
> accesses to graphics memory if the selection is removed in
> vc_do_resize().
> 
> Prevent such out-of-memory accesses by dropping the selection before the
> various con_font_set() console handlers are called.
> 
> Signed-off-by: Helge Deller <deller@....de>

Tested-by: Khalid Masum <khalid.masum.92@...il.com>

> Reported-by: syzbot+14b0e8f3fd1612e35350@...kaller.appspotmail.com
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index dfc1f4b445f3..3f09205185a4 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -4662,9 +4662,11 @@ static int con_font_set(struct vc_data *vc, struct console_font_op *op)
>   	console_lock();
>   	if (vc->vc_mode != KD_TEXT)
>   		rc = -EINVAL;
> -	else if (vc->vc_sw->con_font_set)
> +	else if (vc->vc_sw->con_font_set) {
> +		if (vc_is_sel(vc))
> +			clear_selection();
>   		rc = vc->vc_sw->con_font_set(vc, &font, op->flags);
> -	else
> +	} else
>   		rc = -ENOSYS;
>   	console_unlock();
>   	kfree(font.data);
> @@ -4691,9 +4693,11 @@ static int con_font_default(struct vc_data *vc, struct console_font_op *op)
>   		console_unlock();
>   		return -EINVAL;
>   	}
> -	if (vc->vc_sw->con_font_default)
> +	if (vc->vc_sw->con_font_default) {
> +		if (vc_is_sel(vc))
> +			clear_selection();
>   		rc = vc->vc_sw->con_font_default(vc, &font, s);
> -	else
> +	} else
>   		rc = -ENOSYS;
>   	console_unlock();
>   	if (!rc) {