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

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Date:	Mon, 19 Mar 2012 15:39:00 +0000
From:	David Howells <dhowells@...hat.com>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	dhowells@...hat.com, 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

Jeff Layton <jlayton@...hat.com> wrote:

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

Simple.  This key_put() is called from within keyring_destroy() and that is
only ever called from the garbage collector - which is non-reentrant.  Add to
that that key_put() never actually destroys a now-unused key, but merely
schedules the gc for a future run, and it's *that* that searches out unused
keys and deletes them.

David
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