[PATCH V2] ppdev: Add an error check in register_device

[Huai-Yuan Liu <qq810974084@gmail.com>]

In register_device, the return value of ida_simple_get is unchecked, 
in witch ida_simple_get will use an invalid index value.

To address this issue, index should be checked after ida_simple_get. When
the index value is abnormal, a warning message should be printed, the port
should be dropped, and the value should be recorded, then jump to 'err'.

Fixes: 9a69645dde11 ("ppdev: fix registering same device name")
Signed-off-by: Huai-Yuan Liu <qq810974084@gmail.com>
---
V2:
* In patch V2, we found that parport_find_number implicitly calls 
parport_get_port(). So when dealing with abnormal index values, we should
call parport_put_port() to throw away the reference to the port.
---
 drivers/char/ppdev.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/char/ppdev.c b/drivers/char/ppdev.c
index 4c188e9e477c..ac5a93d39fbd 100644
--- a/drivers/char/ppdev.c
+++ b/drivers/char/ppdev.c
@@ -300,6 +300,13 @@ static int register_device(int minor, struct pp_struct *pp)
 	}
 
 	index = ida_simple_get(&ida_index, 0, 0, GFP_KERNEL);
+	if (index < 0) {
+		pr_warn("%s: failed to get index!\n", name);
+		parport_put_port(port);
+		rc = index;
+		goto err;
+	}
+
 	memset(&ppdev_cb, 0, sizeof(ppdev_cb));
 	ppdev_cb.irq_func = pp_irq;
 	ppdev_cb.flags = (pp->flags & PP_EXCL) ? PARPORT_FLAG_EXCL : 0;
-- 
2.34.1