linux-kernel - Re: [RFC][PATCH 1/9] klp: Fix obvious RCU fail

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Date:	Mon, 2 Mar 2015 15:07:08 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, rusty@...tcorp.com.au,
	mathieu.desnoyers@...icios.com, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, rostedt@...dmis.org, tglx@...utronix.de,
	Seth Jennings <sjenning@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Miroslav Benes <mbenes@...e.cz>, Petr Mladek <pmladek@...e.cz>,
	Jiri Kosina <jkosina@...e.cz>
Subject: Re: [RFC][PATCH 1/9] klp: Fix obvious RCU fail

On Sat, Feb 28, 2015 at 10:24:48PM +0100, Peter Zijlstra wrote:
> While one must hold RCU-sched (aka. preempt_disable) for find_symbol()
> one must equally hold it over the use of the object returned.
> 
> The moment you release the RCU-sched read lock, the object can be dead
> and gone.
> 
> Cc: Seth Jennings <sjenning@...hat.com>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Miroslav Benes <mbenes@...e.cz>
> Cc: Petr Mladek <pmladek@...e.cz>
> Cc: Jiri Kosina <jkosina@...e.cz>
> Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>

> ---
>  kernel/livepatch/core.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -248,11 +248,12 @@ static int klp_find_external_symbol(stru
>  	/* first, check if it's an exported symbol */
>  	preempt_disable();
>  	sym = find_symbol(name, NULL, NULL, true, true);
> -	preempt_enable();
>  	if (sym) {
>  		*addr = sym->value;
> +		preempt_enable();
>  		return 0;
>  	}
> +	preempt_enable();
>  
>  	/* otherwise check if it's in another .o within the patch module */
>  	return klp_find_object_symbol(pmod->name, name, addr);
> 
> 

-- 
Josh
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