linux-kernel - Re: [Keyrings] [PATCH 7/9] KEYS: Permit in-place link replacement in keyring list

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Message-ID: <20120319104432.56fe1e66@redhat.com>
Date:	Mon, 19 Mar 2012 10:44:32 -0400
From:	Jeff Layton <jlayton@...hat.com>
To:	David Howells <dhowells@...hat.com>
Cc:	steved@...hat.com, jmorris@...ei.org,
	linux-security-module@...r.kernel.org, keyrings@...ux-nfs.org,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Keyrings] [PATCH 7/9] KEYS: Permit in-place link replacement
 in keyring list

On Wed, 08 Feb 2012 11:04:00 +0000
David Howells <dhowells@...hat.com> wrote:

> @@ -154,11 +164,10 @@ static void keyring_destroy(struct key *keyring)
>  		write_unlock(&keyring_name_lock);
>  	}
>  
> -	klist = rcu_dereference_check(keyring->payload.subscriptions,
> -				      atomic_read(&keyring->usage) == 0);
> +	klist = rcu_access_pointer(keyring->payload.subscriptions);
>  	if (klist) {
>  		for (loop = klist->nkeys - 1; loop >= 0; loop--)
> -			key_put(klist->keys[loop]);
> +			key_put(rcu_access_pointer(klist->keys[loop]));
>  		kfree(klist);
>  	}
>  }

Why is it safe to use key_put(rcu_access_pointer(...)) ? Clearly that
pointer will end up being dereferenced, right?

-- 
Jeff Layton <jlayton@...hat.com>
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