Re: [Xen-devel] kernel panic in skb_copy_bits

[Joe Jin <joe.jin@xxxxxxxxxx>]

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 <joe.jin@xxxxxxxxxx>
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> ---
>  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:
> 
> 



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