linux-kernel - Re: [PATCH] KEYS: Fix RCU handling in key_gc

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Message-ID: <20100504154601.GA20291@us.ibm.com>
Date:	Tue, 4 May 2010 10:46:01 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	David Howells <dhowells@...hat.com>
Cc:	torvalds@...l.org, akpm@...ux-foundation.org,
	paulmck@...ux.vnet.ibm.com, keyrings@...ux-nfs.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KEYS: Fix RCU handling in key_gc_keyring()

Quoting David Howells (dhowells@...hat.com):
> key_gc_keyring() needs to either hold the RCU read lock or hold the keyring
> semaphore if it's going to scan the keyring's list.  Given that it only needs
> to read the key list, and it's doing so under a spinlock, the RCU read lock is
> the thing to use.
> 
> Furthermore, the RCU check added in e7b0a61b7929632d36cf052d9e2820ef0a9c1bfe is
> incorrect as holding the spinlock on key_serial_lock is not grounds for
> assuming a keyring's pointer list can be read safely.  Instead, a simple
> rcu_dereference() inside of the previously mentioned RCU read lock is what we
> want.
> 
> Reported-by: Serge E. Hallyn <serue@...ibm.com>

You're obviously being far too kind.  In apparent trend for last night
I missed the lack of locking here.

> Signed-off-by: David Howells <dhowells@...hat.com>

Acked-by: Serge Hallyn <serue@...ibm.com>

thanks,
-serge
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