netfilter: ipset: Fix race between IPSET_CMD_CREATE and IPSET_CMD_SWAP

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@gmail.com>
Closes: https://lore.kernel.org/netfilter-devel/ZPZqetxOmH+w%2Fmyc@westworld/#r
Tested-by: Kyle Zeng <zengyhkyle@gmail.com>
Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index e564b5174261159173bfda0756480ca554243b7d..35d2f9c9ada0252e01af3bee1faa1f63a0c94498 100644 (file)
--- 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);
                        nfnl_unlock(NFNL_SUBSYS_IPSET);
                        cond_resched();
                        nfnl_lock(NFNL_SUBSYS_IPSET);
-                       __ip_set_put(set);
+                       __ip_set_put_netlink(set);
                }
 
                ip_set_lock(set);