linux-kernel - Re: [PATCH 5/6] IMA: use rbtree instead of radix tree for inode information cache

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Date:	Wed, 20 Oct 2010 10:17:47 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hch@...radead.org, zohar@...ibm.com,
	warthog9@...nel.org, jmorris@...ei.org, kyle@...artin.ca,
	hpa@...or.com, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, mingo@...e.hu,
	viro@...iv.linux.org.uk
Subject: Re: [PATCH 5/6] IMA: use rbtree instead of radix tree for inode
 information cache

On Tue, Oct 19, 2010 at 06:58:39PM -0400, Eric Paris wrote:
> @@ -36,12 +63,11 @@ struct ima_iint_cache *ima_iint_find_get(struct inode *inode)
>  	struct ima_iint_cache *iint;
>  
>  	rcu_read_lock();
> -	iint = radix_tree_lookup(&ima_iint_store, (unsigned long)inode);
> -	if (!iint)
> -		goto out;
> -	kref_get(&iint->refcount);
> -out:
> +	iint = __ima_iint_find(inode);
> +	if (iint)
> +		kref_get(&iint->refcount);
>  	rcu_read_unlock();
> +

This is wrong - the rbtree is protected only by the ima_iint_lock(),
not RCU. Hence you can't do lockless lookups on an rbtree in this
manner as they will race with inserts and deletes.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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