linux-kernel - Re: [PATCH] SELinux: Fix possible NULL pointer dereference in selinux_inode

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Message-ID: <20140109221711.GJ10323@ZenIV.linux.org.uk>
Date:	Thu, 9 Jan 2014 22:17:11 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Eric Paris <eparis@...isplace.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	James Morris <james.l.morris@...cle.com>,
	Paul Moore <paul@...l-moore.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	stable <stable@...r.kernel.org>
Subject: Re: [PATCH] SELinux: Fix possible NULL pointer dereference in
 selinux_inode_permission()

On Thu, Jan 09, 2014 at 10:51:14AM -0500, Steven Rostedt wrote:

> diff --git a/fs/inode.c b/fs/inode.c
> index 4bcdad3..a8f3b88 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -252,16 +252,17 @@ EXPORT_SYMBOL(__destroy_inode);
>  static void i_callback(struct rcu_head *head)
>  {
>  	struct inode *inode = container_of(head, struct inode, i_rcu);
> +	__destroy_inode(inode);
>  	kmem_cache_free(inode_cachep, inode);
>  }
>  
>  static void destroy_inode(struct inode *inode)
>  {
>  	BUG_ON(!list_empty(&inode->i_lru));
> -	__destroy_inode(inode);
> -	if (inode->i_sb->s_op->destroy_inode)
> +	if (inode->i_sb->s_op->destroy_inode) {
> +		__destroy_inode(inode);
>  		inode->i_sb->s_op->destroy_inode(inode);
> -	else
> +	} else
>  		call_rcu(&inode->i_rcu, i_callback);
>  }
>  
No go - idiotify and friends grab mutexes from fsnotify_inode_delete().
Can't do that from rcu callbacks.
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