Re: [PATCH] netfilter: ipset: fix race condition in ipset swap, destroy and test/add/del

[Pablo Neira Ayuso <pablo@netfilter.org>]

Hi,

This means then that Jozsef's patch is fixing the issue that you
reported, then a Tested-by: tag would be nice to have from you :)

If all is OK, then please, let Jozsef submit his own patch to
netfilter-devel@ so it can follow its trip to the nf.git tree.

Thanks!

On Tue, Oct 17, 2023 at 08:52:56PM +0800, xiaolinkui wrote:
> From: Linkui Xiao <xiaolinkui@kylinos.cn>
> 
> There is a race condition which can be demonstrated by the following
> script:
> 
> ipset create hash_ip1 hash:net family inet hashsize 1024 maxelem 1048576
> ipset add hash_ip1 172.20.0.0/16
> ipset add hash_ip1 192.168.0.0/16
> iptables -A INPUT -m set --match-set hash_ip1 src -j ACCEPT
> while [ 1 ]
> do
>         ipset create hash_ip2 hash:net family inet hashsize 1024 maxelem 1048576
>         ipset add hash_ip2 172.20.0.0/16
>         ipset swap hash_ip1 hash_ip2
>         ipset destroy hash_ip2
>         sleep 0.05
> done
> 
> Swap will exchange the values of ref so destroy will see ref = 0 instead of
> ref = 1. So after running this script for a period of time, the following
> race situations may occur:
>         CPU0:                CPU1:
>         ipt_do_table
>         ->set_match_v4
>         ->ip_set_test
>                         ipset swap hash_ip1 hash_ip2
>                         ipset destroy hash_ip2
>         ->hash_net4_kadt
> 
> CPU0 found ipset through the index, and at this time, hash_ip2 has been
> destroyed by CPU1 through name search. So CPU0 will crash when accessing
> set->data in the function hash_net4_kadt.
> 
> With this fix in place swap will wait for the ongoing operations to be
> finished.
> 
> V1->V2 changes:
> - replace ref_netlink with rcu synchonize_rcu()
> 
> Closes: https://lore.kernel.org/all/69e7963b-e7f8-3ad0-210-7b86eebf7f78@netfilter.org/
> Cc: stable@vger.kernel.org
> Suggested-by: Jozsef Kadlecsik <kadlec@netfilter.org>
> Signed-off-by: Linkui Xiao <xiaolinkui@kylinos.cn>
> 
> ---
>  net/netfilter/ipset/ip_set_core.c | 31 ++++++++++++++++++++++++++-----
>  1 file changed, 26 insertions(+), 5 deletions(-)
> 
> diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
> index 35d2f9c9ada0..62ee4de6ffee 100644
> --- a/net/netfilter/ipset/ip_set_core.c
> +++ b/net/netfilter/ipset/ip_set_core.c
> @@ -712,13 +712,18 @@ ip_set_rcu_get(struct net *net, ip_set_id_t index)
>  	struct ip_set_net *inst = ip_set_pernet(net);
>  
>  	rcu_read_lock();
> -	/* ip_set_list itself needs to be protected */
> +	/* ip_set_list and the set pointer need to be protected */
>  	set = rcu_dereference(inst->ip_set_list)[index];
> -	rcu_read_unlock();
>  
>  	return set;
>  }
>  
> +static inline void
> +ip_set_rcu_put(struct ip_set *set __always_unused)
> +{
> +	rcu_read_unlock();
> +}
> +
>  static inline void
>  ip_set_lock(struct ip_set *set)
>  {
> @@ -744,8 +749,10 @@ ip_set_test(ip_set_id_t index, const struct sk_buff *skb,
>  	pr_debug("set %s, index %u\n", set->name, index);
>  
>  	if (opt->dim < set->type->dimension ||
> -	    !(opt->family == set->family || set->family == NFPROTO_UNSPEC))
> +	    !(opt->family == set->family || set->family == NFPROTO_UNSPEC)) {
> +		ip_set_rcu_put(set);
>  		return 0;
> +	}
>  
>  	ret = set->variant->kadt(set, skb, par, IPSET_TEST, opt);
>  
> @@ -764,6 +771,7 @@ ip_set_test(ip_set_id_t index, const struct sk_buff *skb,
>  			ret = -ret;
>  	}
>  
> +	ip_set_rcu_put(set);
>  	/* Convert error codes to nomatch */
>  	return (ret < 0 ? 0 : ret);
>  }
> @@ -780,12 +788,15 @@ ip_set_add(ip_set_id_t index, const struct sk_buff *skb,
>  	pr_debug("set %s, index %u\n", set->name, index);
>  
>  	if (opt->dim < set->type->dimension ||
> -	    !(opt->family == set->family || set->family == NFPROTO_UNSPEC))
> +	    !(opt->family == set->family || set->family == NFPROTO_UNSPEC)) {
> +		ip_set_rcu_put(set);
>  		return -IPSET_ERR_TYPE_MISMATCH;
> +	}
>  
>  	ip_set_lock(set);
>  	ret = set->variant->kadt(set, skb, par, IPSET_ADD, opt);
>  	ip_set_unlock(set);
> +	ip_set_rcu_put(set);
>  
>  	return ret;
>  }
> @@ -802,12 +813,15 @@ ip_set_del(ip_set_id_t index, const struct sk_buff *skb,
>  	pr_debug("set %s, index %u\n", set->name, index);
>  
>  	if (opt->dim < set->type->dimension ||
> -	    !(opt->family == set->family || set->family == NFPROTO_UNSPEC))
> +	    !(opt->family == set->family || set->family == NFPROTO_UNSPEC)) {
> +		ip_set_rcu_put(set);
>  		return -IPSET_ERR_TYPE_MISMATCH;
> +	}
>  
>  	ip_set_lock(set);
>  	ret = set->variant->kadt(set, skb, par, IPSET_DEL, opt);
>  	ip_set_unlock(set);
> +	ip_set_rcu_put(set);
>  
>  	return ret;
>  }
> @@ -882,6 +896,7 @@ ip_set_name_byindex(struct net *net, ip_set_id_t index, char *name)
>  	read_lock_bh(&ip_set_ref_lock);
>  	strscpy_pad(name, set->name, IPSET_MAXNAMELEN);
>  	read_unlock_bh(&ip_set_ref_lock);
> +	ip_set_rcu_put(set);
>  }
>  EXPORT_SYMBOL_GPL(ip_set_name_byindex);
>  
> @@ -1348,6 +1363,9 @@ static int ip_set_rename(struct sk_buff *skb, const struct nfnl_info *info,
>   * protected by the ip_set_ref_lock. The kernel interfaces
>   * do not hold the mutex but the pointer settings are atomic
>   * so the ip_set_list always contains valid pointers to the sets.
> + * However after swapping, a userspace set destroy command could
> + * remove a set still processed by kernel side add/del/test.
> + * Therefore we need to wait for the ongoing operations to be finished.
>   */
>  
>  static int ip_set_swap(struct sk_buff *skb, const struct nfnl_info *info,
> @@ -1397,6 +1415,9 @@ static int ip_set_swap(struct sk_buff *skb, const struct nfnl_info *info,
>  	ip_set(inst, to_id) = from;
>  	write_unlock_bh(&ip_set_ref_lock);
>  
> +	/* Make sure all readers of the old set pointers are completed. */
> +	synchronize_rcu();
> +
>  	return 0;
>  }
>  
> -- 
> 2.17.1
>