[PATCH] tty_io: Fix a missing-check bug in drivers/tty/tty_io.c

[Gen Zhang]

In alloc_tty_struct(), tty->dev is assigned by tty_get_device(). And it
calls class_find_device(). And class_find_device() may return NULL.
And tty->dev is dereferenced in the following codes. When 
tty_get_device() returns NULL, dereferencing this tty->dev null pointer
may cause the kernel go wrong. Thus we should check tty->dev.
Further, if tty_get_device() returns NULL, we should free tty and 
return NULL.

Signed-off-by: Gen Zhang <blackgod016574@xxxxxxxxx>

---
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 033ac7e..1444b59 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3008,6 +3008,10 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx)
 	tty->index = idx;
 	tty_line_name(driver, idx, tty->name);
 	tty->dev = tty_get_device(tty);
+	if (!tty->dev) {
+		kfree(tty);
+		return NULL;
+	}
 
 	return tty;
 }