[Devel] [PATCH 1/2] vznetstat: Add protection to venet_acct_set_classes()

[Andrey Ryabinin]

On 12/19/2017 03:24 PM, Kirill Tkhai wrote:
> It seems there was no synchronization since the time
> when ioctls in kernel were serialized via single mutex.
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  kernel/ve/vznetstat/vznetstat.c |   11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/ve/vznetstat/vznetstat.c b/kernel/ve/vznetstat/vznetstat.c
> index 3a53ce27bde2..a65e05378ff4 100644
> --- a/kernel/ve/vznetstat/vznetstat.c
> +++ b/kernel/ve/vznetstat/vznetstat.c
> @@ -52,6 +52,7 @@ static struct class_info_set *info_v4 = NULL;
>  #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
>  static struct class_info_set *info_v6 = NULL;
>  #endif
> +static DEFINE_MUTEX(info_mutex);
>  
>  /* v6: flag IPv6 classes or IPv4 */
>  static int venet_acct_set_classes(const void __user *user_info, int length, int v6)
> @@ -88,15 +89,17 @@ static int venet_acct_set_classes(const void __user *user_info, int length, int
>  			goto out_free;
>  	}
>  
> -	rcu_read_lock();
> +	mutex_lock(&info_mutex);
>  	if (v6) {
> -		old = rcu_dereference(info_v6);
> +		old = rcu_dereference_protected(info_v6,
> +						lockdep_is_held(&info_mutex));
>  		rcu_assign_pointer(info_v6, info);
>  	} else {
> -		old = rcu_dereference(info_v4);
> +		old = rcu_dereference_protected(info_v4,
> +						lockdep_is_held(&info_mutex));
>  		rcu_assign_pointer(info_v4, info);

It probably would be easier to simply use xchg() here. Locking wouldn't be needed in that case.
But as I assume this is not performance sensitive code, so mutex should be fine.

Acked-by: Andrey Ryabinin <aryabinin at virtuozzo.com>


>  	}
> -	rcu_read_unlock();
> +	mutex_unlock(&info_mutex);
>  
>  	synchronize_net();
>  	/* IMPORTANT. I think reset of statistics collected should not be
>