[patch] hiddev: fix incorrect hiddev freeing

[Johannes Weiner]

When hiddev_open() fails for whatever reason, free the just allocated
hiddev_list structure shared hiddev potentially still in use.

The hiddev is freed in device disconnect/last close of the device file
and must not be freed while there are possibly existing references to
it.

This is probably responsible for these

  http://kerneloops.org/oops.php?number=221185
  http://kerneloops.org/oops.php?number=220365

where a reader sleeps on the waitqueue, the device gets disconnected
(exist -> 0) another user tries to open it, fails on the exist check
and frees the hiddev from the table.  The finish_wait() in the reader
will then dereference the hiddev to get to the waitqueue and oopses.

This was introduced by commit 079034073faf974973baa0256b029451f6e768ad
"HID: hiddev cleanup -- handle all error conditions properly".

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Oliver Neukum <oliver@xxxxxxxxxxx>
---

diff --git a/drivers/hid/usbhid/hiddev.c b/drivers/hid/usbhid/hiddev.c
index 4940e4d..00ea1ed 100644
--- a/drivers/hid/usbhid/hiddev.c
+++ b/drivers/hid/usbhid/hiddev.c
@@ -306,7 +306,7 @@ static int hiddev_open(struct inode *inode, struct file *file)
 	return 0;
 bail:
 	file->private_data = NULL;
-	kfree(list->hiddev);
+	kfree(list);
 	return res;
 }
 
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