Subject: Re: [PATCH net-2.6.25] [IPV6] ADDRLABEL: Fix double free on label deletion.

From: "Paul E. McKenney" <[email-masked]>
Date: Tue, 29 Jan 2008 12:59:13 -0800

On Mon, Jan 28, 2008 at 09:02:22PM +0900, YOSHIFUJI Hideaki / 吉藤英明 wrote:
> If an entry is being deleted because it has only one reference, 
> we immediately delete it and blindly register the rcu handler for it,
> This results in oops by double freeing that object.
> 
> This patch fixes it by consolidating the code paths for the deletion;
> let its rcu handler delete the object if it has no more reference.
> 
> Bug was found by Mitsuru Chinen <[email-masked]>

Good catch!!!

Acked-by: Paul E. McKenney <[email-masked]>

> Signed-off-by: YOSHIFUJI Hideaki <[email-masked]>
> ---
> 
> diff --git a/net/ipv6/addrlabel.c b/net/ipv6/addrlabel.c
> index 6f1ca60..7a706c4 100644
> --- a/net/ipv6/addrlabel.c
> +++ b/net/ipv6/addrlabel.c
> @@ -106,6 +106,11 @@ static inline void ip6addrlbl_free(struct ip6addrlbl_entry *p)
>  	kfree(p);
>  }
> 
> +static void ip6addrlbl_free_rcu(struct rcu_head *h)
> +{
> +	ip6addrlbl_free(container_of(h, struct ip6addrlbl_entry, rcu));
> +}
> +
>  static inline int ip6addrlbl_hold(struct ip6addrlbl_entry *p)
>  {
>  	return atomic_inc_not_zero(&p->refcnt);
> @@ -114,12 +119,7 @@ static inline int ip6addrlbl_hold(struct ip6addrlbl_entry *p)
>  static inline void ip6addrlbl_put(struct ip6addrlbl_entry *p)
>  {
>  	if (atomic_dec_and_test(&p->refcnt))
> -		ip6addrlbl_free(p);
> -}
> -
> -static void ip6addrlbl_free_rcu(struct rcu_head *h)
> -{
> -	ip6addrlbl_free(container_of(h, struct ip6addrlbl_entry, rcu));
> +		call_rcu(&p->rcu, ip6addrlbl_free_rcu);
>  }
> 
>  /* Find label */
> @@ -240,7 +240,6 @@ int __ip6addrlbl_add(struct ip6addrlbl_entry *newp, int replace)
>  				}
>  				hlist_replace_rcu(&p->list, &newp->list);
>  				ip6addrlbl_put(p);
> -				call_rcu(&p->rcu, ip6addrlbl_free_rcu);
>  				goto out;
>  			} else if ((p->prefixlen == newp->prefixlen && !p->ifindex) ||
>  				   (p->prefixlen < newp->prefixlen)) {
> @@ -300,7 +299,6 @@ int __ip6addrlbl_del(const struct in6_addr *prefix, int prefixlen,
>  		    ipv6_addr_equal(&p->prefix, prefix)) {
>  			hlist_del_rcu(&p->list);
>  			ip6addrlbl_put(p);
> -			call_rcu(&p->rcu, ip6addrlbl_free_rcu);
>  			ret = 0;
>  			break;
>  		}
> 
> -- 
> YOSHIFUJI Hideaki @ USAGI Project  <[email-masked]>
> GPG-FP  : 9022 65EB 1ECF 3AD1 0BDF  80D8 4807 F894 E062 0EEA
> --
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