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.or... 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 26613e3731d02..24f81826ed4a5 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 @@ -1407,6 +1404,9 @@ static int ip_set_swap(struct net *net, struct sock *ctnl, struct sk_buff *skb, 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; }