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@gmx.de>
Reported-by: syzbot+14b0e8f3fd1612e35350@syzkaller.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) {

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@gmx.de>

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

> Reported-by: syzbot+14b0e8f3fd1612e35350@syzkaller.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) {