[PATCH v4 3/5] tty: skip cdev_del() when no cdev is registered

[Karl Mehltretter <kmehltretter@gmail.com>]

TTY device registration can fail before a cdev is allocated.
Serial core keeps the port so setserial can still use it, and later
removal passes the NULL cdev slot to cdev_del(), causing a NULL-pointer
dereference.

Only delete the cdev when the slot is not NULL.

Fixes: a3a10ce3429e ("Avoid usb reset crashes by making tty_io cdevs truly dynamic")
Fixes: da4c279942b0 ("serial: enable serdev support")
Assisted-by: Claude:claude-fable-5
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
---
 drivers/tty/tty_io.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 6b283fd03ff8..e742bf9d8631 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3305,7 +3305,7 @@ EXPORT_SYMBOL_GPL(tty_register_device_attr);
 void tty_unregister_device(struct tty_driver *driver, unsigned index)
 {
 	device_destroy(&tty_class, MKDEV(driver->major, driver->minor_start) + index);
-	if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
+	if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC) && driver->cdevs[index]) {
 		cdev_del(driver->cdevs[index]);
 		driver->cdevs[index] = NULL;
 	}
-- 
2.53.0