vt: clear selection before resizing

When resizing a vt its selection may exceed the new size, resulting in
an invalid memory access [1]. Clear the selection before resizing.

[1] http://lkml.kernel.org/r/CACT4Y+acDTwy4umEvf5ROBGiRJNrxHN4Cn5szCXE5Jw-d1B=Xw@mail.gmail.com

Reported-and-tested-by: Dmitry Vyukov <[email protected]>
Signed-off-by: Scot Doyle <[email protected]>
Cc: stable <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Scot Doyle

drivers/tty/vt/vt.c

@@ -876,6 +876,9 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
 	if (!newscreen)
 		return -ENOMEM;
 
+	if (vc == sel_cons)
+		clear_selection();
+
 	old_rows = vc->vc_rows;
 	old_row_size = vc->vc_size_row;