linux-kernel - [RFC] Input: Remove unsafe device module references

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Date:	Tue,  1 Nov 2011 16:41:40 +0100
From:	David Herrmann <dh.herrmann@...glemail.com>
To:	linux-input@...r.kernel.org
Cc:	dmitry.torokhov@...il.com, gregkh@...e.de,
	linux-kernel@...r.kernel.org,
	David Herrmann <dh.herrmann@...glemail.com>
Subject: [RFC] Input: Remove unsafe device module references

Hi Dmitry and Greg

It doesn't make sense to take a reference to our own module. When we call
module_put(THIS_MODULE) we cannot make sure that our module is still alive when
this function returns. Therefore, module_put() will return to invalid memory and
our input_dev_release() function is no longer available.

It would be interesting if Greg could elaborate what else we could do to replace
this module-refcount as it is definitely needed here. However, "struct device"
doesn't provide an owner field so there is no way for us to let the device core
keep a reference to our module.

I have no clue what to do here but the current implementation is definitely
unsafe so this is marked as RFC. Currently, the device_attributes probably
already keep a reference to our module so applying this patch would probably not
break anything, however, this does not look like something we can trust on.

My bug-thread kind of died (https://lkml.org/lkml/2011/10/29/75) so I now try to
show this with an example here.

Regards
David

Signed-off-by: David Herrmann <dh.herrmann@...glemail.com>
---
 drivers/input/input.c |    4 ----
 1 files changed, 0 insertions(+), 4 deletions(-)

diff --git a/drivers/input/input.c b/drivers/input/input.c
index da38d97..f691502 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c
@@ -1417,8 +1417,6 @@ static void input_dev_release(struct device *device)
 	input_mt_destroy_slots(dev);
 	kfree(dev->absinfo);
 	kfree(dev);
-
-	module_put(THIS_MODULE);
 }

 /*
@@ -1657,8 +1655,6 @@ struct input_dev *input_allocate_device(void)
 		spin_lock_init(&dev->event_lock);
 		INIT_LIST_HEAD(&dev->h_list);
 		INIT_LIST_HEAD(&dev->node);
-
-		__module_get(THIS_MODULE);
 	}

 	return dev;
-- 
1.7.7.1

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