Subject: Re: [PATCH][IPVS] Fix sched registration race when checking for name collision

From: Simon Horman <[email-masked]>
Date: Tue, 4 Dec 2007 10:41:43 +0900

On Mon, Dec 03, 2007 at 01:10:57PM +0300, Pavel Emelyanov wrote:
> The register_ip_vs_scheduler() checks for the scheduler with the
> same name under the read-locked __ip_vs_sched_lock, then drops,
> takes it for writing and puts the scheduler in list.
> 
> This is racy, since we can have a race window between the lock
> being re-locked for writing.
> 
> The fix is to search the scheduler with the given name right under
> the write-locked __ip_vs_sched_lock.

This looks correct to me.

> Signed-off-by: Pavel Emelyanov <[email-masked]>

Acked-by: Simon Horman <[email-masked]>

> ---
> 
> diff --git a/net/ipv4/ipvs/ip_vs_sched.c b/net/ipv4/ipvs/ip_vs_sched.c
> index 1602304..4322358 100644
> --- a/net/ipv4/ipvs/ip_vs_sched.c
> +++ b/net/ipv4/ipvs/ip_vs_sched.c
> @@ -183,19 +183,6 @@ int register_ip_vs_scheduler(struct ip_vs_scheduler *scheduler)
>  	/* increase the module use count */
>  	ip_vs_use_count_inc();
>  
> -	/*
> -	 *  Make sure that the scheduler with this name doesn't exist
> -	 *  in the scheduler list.
> -	 */
> -	sched = ip_vs_sched_getbyname(scheduler->name);
> -	if (sched) {
> -		ip_vs_scheduler_put(sched);
> -		ip_vs_use_count_dec();
> -		IP_VS_ERR("register_ip_vs_scheduler(): [%s] scheduler "
> -			  "already existed in the system\n", scheduler->name);
> -		return -EINVAL;
> -	}
> -
>  	write_lock_bh(&__ip_vs_sched_lock);
>  
>  	if (scheduler->n_list.next != &scheduler->n_list) {
> @@ -207,6 +194,20 @@ int register_ip_vs_scheduler(struct ip_vs_scheduler *scheduler)
>  	}
>  
>  	/*
> +	 *  Make sure that the scheduler with this name doesn't exist
> +	 *  in the scheduler list.
> +	 */
> +	list_for_each_entry(sched, &ip_vs_schedulers, n_list) {
> +		if (strcmp(scheduler->name, sched->name) == 0) {
> +			write_unlock_bh(&__ip_vs_sched_lock);
> +			ip_vs_use_count_dec();
> +			IP_VS_ERR("register_ip_vs_scheduler(): [%s] scheduler "
> +					"already existed in the system\n",
> +					scheduler->name);
> +			return -EINVAL;
> +		}
> +	}
> +	/*
>  	 *	Add it into the d-linked scheduler list
>  	 */
>  	list_add(&scheduler->n_list, &ip_vs_schedulers);

-- 
Horms