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netfilter: ipset: fix race condition between swap/destroy and kernel side add/del/test

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Linkui Xiao reported that there's a race condition when ipset swap and destroy is
called, which can lead to crash in add/del/test element operations. Swap then
destroy are usual operations to replace a set with another one in a production
system. The issue can in some cases be reproduced with the 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
	# ... Ongoing traffic...
        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

In the race case the possible order of the operations are

	CPU0			CPU1
	ip_set_test
				ipset swap hash_ip1 hash_ip2
				ipset destroy hash_ip2
	hash_net_kadt

Swap replaces hash_ip1 with hash_ip2 and then destroy removes hash_ip2 which
is the original hash_ip1. ip_set_test was called on hash_ip1 and because destroy
removed it, hash_net_kadt crashes.

The fix is to force ip_set_swap() to wait for all readers to finish accessing the
old set pointers by calling synchronize_rcu().

The first version of the patch was written by Linkui Xiao <xiaolinkui@kylinos.cn>.

v2: synchronize_rcu() is moved into ip_set_swap() in order not to burden
    ip_set_destroy() unnecessarily when all sets are destroyed.
v3: Florian Westphal pointed out that all netfilter hooks run with rcu_read_lock() held
    and em_ipset.c wraps the entire ip_set_test() in rcu read lock/unlock pair.
    So there's no need to extend the rcu read locked area in ipset itself.

Closes: https://lore.kernel.org/all/69e7963b-e7f8-3ad0-210-7b86eebf7f78@netfilter.org/
Reported by: Linkui Xiao <xiaolinkui@kylinos.cn>
Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Jozsef Kadlecsik 2023-11-13 21:13:23 +01:00 committed by Pablo Neira Ayuso
parent a7d5a955bf
commit 28628fa952
1 changed files with 7 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
net/netfilter/ipset/ip_set_core.c
View File

@ -61,6 +61,8 @@ MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_IPSET);
ip_set_dereference((inst)->ip_set_list)[id]
#define ip_set_ref_netlink(inst,id) \
rcu_dereference_raw((inst)->ip_set_list)[id]
#define ip_set_dereference_nfnl(p) \
rcu_dereference_check(p, lockdep_nfnl_is_held(NFNL_SUBSYS_IPSET))
/* The set types are implemented in modules and registered set types
* can be found in ip_set_type_list. Adding/deleting types is
@ -708,15 +710,10 @@ __ip_set_put_netlink(struct ip_set *set)
static struct ip_set *
ip_set_rcu_get(struct net *net, ip_set_id_t index)
{
struct ip_set *set;
struct ip_set_net *inst = ip_set_pernet(net);
rcu_read_lock();
/* ip_set_list itself needs to be protected */
set = rcu_dereference(inst->ip_set_list)[index];
rcu_read_unlock();
return set;
/* ip_set_list and the set pointer need to be protected */
return ip_set_dereference_nfnl(inst->ip_set_list)[index];
}
static inline void
@ -1397,6 +1394,9 @@ 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;
}