[PATCH 2/2] netfilter: ipset: fix race condition in ipset swap, destroy and test

[xiaolinkui <xiaolinkui@gmail.com>]

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 not succeed because ip_set_test still has
ref_swapping on the set.

Both destroy and swap will error out if ref_swapping != 0 on the set.

Signed-off-by: Linkui Xiao <xiaolinkui@kylinos.cn>
---
 net/netfilter/ipset/ip_set_core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index e5d25df5c64c..d6bd37010bfb 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -741,11 +741,13 @@ ip_set_test(ip_set_id_t index, const struct sk_buff *skb,
 	int ret = 0;
 
 	BUG_ON(!set);
+
+	__ip_set_get_swapping(set);
 	pr_debug("set %s, index %u\n", set->name, index);
 
 	if (opt->dim < set->type->dimension ||
 	    !(opt->family == set->family || set->family == NFPROTO_UNSPEC))
-		return 0;
+		goto out;
 
 	ret = set->variant->kadt(set, skb, par, IPSET_TEST, opt);
 
@@ -764,6 +766,8 @@ ip_set_test(ip_set_id_t index, const struct sk_buff *skb,
 			ret = -ret;
 	}
 
+out:
+	__ip_set_put_swapping(set);
 	/* Convert error codes to nomatch */
 	return (ret < 0 ? 0 : ret);
 }
-- 
2.17.1