[PATCH AUTOSEL 6.5 05/15] netfilter: ipset: fix race condition between swap/destroy and kernel side add/del/test

Sasha Levin
2023-11-22T15:36:01Z

From: Jozsef Kadlecsik <kadlec@netfilter.org>

[ Upstream commit 28628fa952fefc7f2072ce6e8016968cc452b1ba ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/ipset/ip_set_core.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index 58608460cf6df..809b9b1a88afc 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -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;
}

--
2.42.0