[PATCH 4.9 06/42] vt: Clear selection before changing the font

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Helge Deller <deller@gmx.de>

commit 566f9c9f89337792070b5a6062dff448b3e7977f upstream.

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.

Reported-by: syzbot+14b0e8f3fd1612e35350@syzkaller.appspotmail.com
Cc: stable <stable@kernel.org>
Tested-by: Khalid Masum <khalid.masum.92@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
Link: https://lore.kernel.org/r/YuV9apZGNmGfjcor@p100
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/vt/vt.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -4183,9 +4183,11 @@ static int con_font_set(struct vc_data *
 	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);
@@ -4212,9 +4214,11 @@ static int con_font_default(struct vc_da
 		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) {