linux-kernel - Re: [PATCH v3 16/24] locking/lockdep: Retain the class key and name while freeing a lock class

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Date:   Fri, 7 Dec 2018 11:21:43 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     mingo@...hat.com, tj@...nel.org, longman@...hat.com,
        johannes.berg@...el.com, linux-kernel@...r.kernel.org,
        Johannes Berg <johannes@...solutions.net>
Subject: Re: [PATCH v3 16/24] locking/lockdep: Retain the class key and name
 while freeing a lock class

On Thu, Dec 06, 2018 at 05:11:40PM -0800, Bart Van Assche wrote:
> The next patch in this series uses the class name in code that
> detects calls to lock_acquire() while a class key is being freed. Hence
> retain the class name for lock classes that are being freed.

>From readin the discussion with v2; you meant to say: 'uses the class
name pointer', right? You're not actually ever going to dereference it,
since that would be a UaF.

> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Waiman Long <longman@...hat.com>
> Cc: Johannes Berg <johannes@...solutions.net>
> Signed-off-by: Bart Van Assche <bvanassche@....org>
> ---
>  kernel/locking/lockdep.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index ecd92969674c..92bdb187987f 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -4147,10 +4147,8 @@ static void zap_class(struct lock_class *class)
>  	 * Unhash the class and remove it from the all_lock_classes list:
>  	 */
>  	hlist_del_rcu(&class->hash_entry);
> +	class->hash_entry.pprev = NULL;
>  	list_del(&class->lock_entry);
> -
> -	RCU_INIT_POINTER(class->key, NULL);
> -	RCU_INIT_POINTER(class->name, NULL);
>  }
>  
>  static inline int within(const void *addr, void *start, unsigned long size)
> -- 
> 2.20.0.rc2.403.gdbc3b29805-goog
>