Subject: Re: kernel panic in skb_copy_bits

From: Joe Jin <[email-masked]>
Date: Fri, 28 Jun 2013 19:33:03 +0800

Hi Eric,

Thanks for your patch, I'll test it then get back to you.

Regards,
Joe
On 06/28/13 17:37, Eric Dumazet wrote:
> OK please try the following patch
> 
> 
> [PATCH] neighbour: fix a race in neigh_destroy()
> 
> There is a race in neighbour code, because neigh_destroy() uses
> skb_queue_purge(&neigh->arp_queue) without holding neighbour lock,
> while other parts of the code assume neighbour rwlock is what
> protects arp_queue
> 
> Convert all skb_queue_purge() calls to the __skb_queue_purge() variant
> 
> Use __skb_queue_head_init() instead of skb_queue_head_init()
> to make clear we do not use arp_queue.lock
> 
> And hold neigh->lock in neigh_destroy() to close the race.
> 
> Reported-by: Joe Jin <[email-masked]>
> Signed-off-by: Eric Dumazet <[email-masked]>
> ---
>  net/core/neighbour.c |   12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 2569ab2..b7de821 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -231,7 +231,7 @@ static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev)
>  				   we must kill timers etc. and move
>  				   it to safe state.
>  				 */
> -				skb_queue_purge(&n->arp_queue);
> +				__skb_queue_purge(&n->arp_queue);
>  				n->arp_queue_len_bytes = 0;
>  				n->output = neigh_blackhole;
>  				if (n->nud_state & NUD_VALID)
> @@ -286,7 +286,7 @@ static struct neighbour *neigh_alloc(struct neigh_table *tbl, struct net_device
>  	if (!n)
>  		goto out_entries;
>  
> -	skb_queue_head_init(&n->arp_queue);
> +	__skb_queue_head_init(&n->arp_queue);
>  	rwlock_init(&n->lock);
>  	seqlock_init(&n->ha_lock);
>  	n->updated	  = n->used = now;
> @@ -708,7 +708,9 @@ void neigh_destroy(struct neighbour *neigh)
>  	if (neigh_del_timer(neigh))
>  		pr_warn("Impossible event\n");
>  
> -	skb_queue_purge(&neigh->arp_queue);
> +	write_lock_bh(&neigh->lock);
> +	__skb_queue_purge(&neigh->arp_queue);
> +	write_unlock_bh(&neigh->lock);
>  	neigh->arp_queue_len_bytes = 0;
>  
>  	if (dev->netdev_ops->ndo_neigh_destroy)
> @@ -858,7 +860,7 @@ static void neigh_invalidate(struct neighbour *neigh)
>  		neigh->ops->error_report(neigh, skb);
>  		write_lock(&neigh->lock);
>  	}
> -	skb_queue_purge(&neigh->arp_queue);
> +	__skb_queue_purge(&neigh->arp_queue);
>  	neigh->arp_queue_len_bytes = 0;
>  }
>  
> @@ -1210,7 +1212,7 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new,
>  
>  			write_lock_bh(&neigh->lock);
>  		}
> -		skb_queue_purge(&neigh->arp_queue);
> +		__skb_queue_purge(&neigh->arp_queue);
>  		neigh->arp_queue_len_bytes = 0;
>  	}
>  out:
> 
>