netdev - Re: [RFC PATCH net-next 1/2] devlink: Hold a reference on parent device

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Message-ID: <ZJPqS0Di6Cg9JT3D@nanopsycho>
Date: Thu, 22 Jun 2023 08:29:31 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Ido Schimmel <idosch@...dia.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
	pabeni@...hat.com, edumazet@...gle.com, petrm@...dia.com
Subject: Re: [RFC PATCH net-next 1/2] devlink: Hold a reference on parent
 device

Wed, Jun 21, 2023 at 05:35:15PM CEST, idosch@...dia.com wrote:
>On Wed, Jun 21, 2023 at 01:48:36PM +0200, Jiri Pirko wrote:
>> Mon, Jun 19, 2023 at 02:50:14PM CEST, idosch@...dia.com wrote:
>> >@@ -91,6 +92,7 @@ static void devlink_release(struct work_struct *work)
>> > 
>> > 	mutex_destroy(&devlink->lock);
>> > 	lockdep_unregister_key(&devlink->lock_key);
>> >+	put_device(devlink->dev);
>> 
>> In this case I think you have to make sure this is called before
>> devlink_free() ends. After the caller of devlink_free() returns (most
>> probably .remove callback), nothing stops module from being removed.
>> 
>> I don't see other way. Utilize complete() here and wait_for_completion()
>> at the end of devlink_free().
>
>I might be missing something, but how can I do something like
>wait_for_completion(&devlink->comp) at the end of devlink_free()? After
>I call devlink_put() the devlink instance can be freed and the
>wait_for_completion() call will result in a UAF.

You have to move the free() to devlink_free()
Basically, all the things done in devlink_put that are symmetrical to
the initialization done in devlink_alloc() should be moved there.


>
>> 
>> If the completion in devlink_put() area rings a bell for you, let me save
>> you the trouble looking it up:
>> 9053637e0da7 ("devlink: remove the registration guarantee of references")
>> This commit removed that. But it is a different usage.
>> 
>> 
>> 
>> > 	kfree(devlink);
>> > }
>> > 
>> >@@ -204,6 +206,7 @@ struct devlink *devlink_alloc_ns(const struct devlink_ops *ops,
>> > 	if (ret < 0)
>> > 		goto err_xa_alloc;
>> > 
>> >+	get_device(dev);
>> > 	devlink->dev = dev;
>> > 	devlink->ops = ops;
>> > 	xa_init_flags(&devlink->ports, XA_FLAGS_ALLOC);
>> >-- 
>> >2.40.1
>> >