[PATCH v2 1/3] vt: fix check for system/busy console drivers when unregistering them

[Imre Deak]

System console drivers (without the CON_DRIVER_FLAG_MODULE flag) and
busy drivers bound to a console (as reported by con_is_bound())
shouldn't be unregistered. The current code checks for the
CON_DRIVER_FLAG_INIT flag but this doesn't really correspond to either
of the above two conditions. CON_DRIVER_FLAG_INIT is set whenever its
associated console's con_startup() function is called, which first
happens when the console driver is registered (so before the console
gets bound) and gets cleared when the console gets unbound. The
purpose of this flag is to show if we need to call con_startup() on a
console before we use it.

Based on the above, do_unregister_con_driver() in its current form will
incorrectly allow unregistering a console driver only if it was never
bound, but will refuse to unregister one that was bound and later
unbound. It will also allow unregistering a system console driver.

Fix this by checking for CON_DRIVER_FLAG_MODULE to allow non-system
console drivers to unregister and prevent system console drivers from
unregistering. Rely on the existing con_is_bound() check earlier in the
function to refuse unregistering a busy console driver.

v2:
- reword the third paragraph to clarify how the fix works (Peter Hurley)

Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
---
 drivers/tty/vt/vt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index b33b00b..1862e89 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -3660,7 +3660,7 @@ int do_unregister_con_driver(const struct consw *csw)
 		struct con_driver *con_driver = &registered_con_driver[i];
 
 		if (con_driver->con == csw &&
-		    con_driver->flag & CON_DRIVER_FLAG_INIT) {
+		    con_driver->flag & CON_DRIVER_FLAG_MODULE) {
 			vtconsole_deinit_device(con_driver);
 			device_destroy(vtconsole_class,
 				       MKDEV(0, con_driver->node));
-- 
1.8.4

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