netdev - Re: [PATCH net-next 1/1] tipc: eliminate risk of finding to-be-deleted node instance

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Message-Id: <20160225.170633.2220739017957131099.davem@davemloft.net>
Date:	Thu, 25 Feb 2016 17:06:33 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	jon.maloy@...csson.com
Cc:	netdev@...r.kernel.org, paul.gortmaker@...driver.com,
	parthasarathy.bhuvaragan@...csson.com, richard.alpe@...csson.com,
	ying.xue@...driver.com, maloy@...jonn.com,
	tipc-discussion@...ts.sourceforge.net
Subject: Re: [PATCH net-next 1/1] tipc: eliminate risk of finding
 to-be-deleted node instance

From: Jon Maloy <jon.maloy@...csson.com>
Date: Wed, 24 Feb 2016 11:00:19 -0500

> Although we have never seen it happen, we have identified the
> following problematic scenario when nodes are stopped and deleted:
> 
> CPU0:                            CPU1:
> 
> tipc_node_xxx()                                   //ref == 1
>    tipc_node_put()                                //ref -> 0
>                                  tipc_node_find() // node still in table
>        tipc_node_delete()
>          list_del_rcu(n. list)
>                                  tipc_node_get()  //ref -> 1, bad
>          kfree_rcu()
> 
>                                  tipc_node_put() //ref to 0 again.
>                                  kfree_rcu()     // BOOM!
> 
> We fix this by introducing use of the conditional kref_get_if_not_zero()
> instead of kref_get() in the function tipc_node_find(). This eliminates
> any risk of post-mortem access.
> 
> Reported-by: Zhijiang Hu <huzhijiang@...il.com>
> Acked-by: Ying Xue <ying.xue@...driver.com>
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>

Applied.