[PATCH 1/1] netfilter: ipset: Fix race between IPSET_CMD_CREATE and IPSET_CMD_SWAP

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Kyle Zeng reported that there is a race between IPSET_CMD_ADD and IPSET_CMD_SWAP
in netfilter/ip_set, which can lead to the invocation of `__ip_set_put` on a wrong
`set`, triggering the `BUG_ON(set->ref == 0);` check in it.

The race is caused by using the wrong reference counter, i.e. the ref counter instead
of ref_netlink.

Fixes: 24e227896bbf ("netfilter: ipset: Add schedule point in call_ad().")
Reported-by: Kyle Zeng <zengyhkyle@xxxxxxxxx>
Tested-by: Kyle Zeng <zengyhkyle@xxxxxxxxx>
Signed-off-by: Jozsef Kadlecsik <kadlec@xxxxxxxxxxxxx>
 net/netfilter/ipset/ip_set_core.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index e564b5174261..35d2f9c9ada0 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -682,6 +682,14 @@ __ip_set_put(struct ip_set *set)
 /* set->ref can be swapped out by ip_set_swap, netlink events (like dump) need
  * a separate reference counter
+static void
+__ip_set_get_netlink(struct ip_set *set)
+	write_lock_bh(&ip_set_ref_lock);
+	set->ref_netlink++;
+	write_unlock_bh(&ip_set_ref_lock);
 static void
 __ip_set_put_netlink(struct ip_set *set)
@@ -1693,11 +1701,11 @@ call_ad(struct net *net, struct sock *ctnl, struct sk_buff *skb,
 	do {
 		if (retried) {
-			__ip_set_get(set);
+			__ip_set_get_netlink(set);
-			__ip_set_put(set);
+			__ip_set_put_netlink(set);

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