ipvs: Defer ip_vs_ftp unregister during netns cleanup

[ Upstream commit 134121bfd99a06d44ef5ba15a9beb075297c0821 ]

On the netns cleanup path, __ip_vs_ftp_exit() may unregister ip_vs_ftp
before connections with valid cp->app pointers are flushed, leading to a
use-after-free.

Fix this by introducing a global `exiting_module` flag, set to true in
ip_vs_ftp_exit() before unregistering the pernet subsystem. In
__ip_vs_ftp_exit(), skip ip_vs_ftp unregister if called during netns
cleanup (when exiting_module is false) and defer it to
__ip_vs_cleanup_batch(), which unregisters all apps after all connections
are flushed. If called during module exit, unregister ip_vs_ftp
immediately.

Fixes: 61b1ab4 ("IPVS: netns, add basic init per netns.")
Suggested-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Slavin Liu <slavin452@gmail.com>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Ulrich Hecht <uli@kernel.org>

Author: slavin-ayu

net/netfilter/ipvs/ip_vs_ftp.c

@@ -59,6 +59,7 @@ enum {
 	IP_VS_FTP_EPSV,
 };
 
+static bool exiting_module;
 /*
  * List of ports (up to IP_VS_APP_MAX_PORTS) to be handled by helper
  * First port is set to the default port.
@@ -613,7 +614,7 @@ static void __ip_vs_ftp_exit(struct net *net)
 {
 	struct netns_ipvs *ipvs = net_ipvs(net);
 
-	if (!ipvs)
+	if (!ipvs || !exiting_module)
 		return;
 
 	unregister_ip_vs_app(ipvs, &ip_vs_ftp);
@@ -635,6 +636,7 @@ static int __init ip_vs_ftp_init(void)
  */
 static void __exit ip_vs_ftp_exit(void)
 {
+	exiting_module = true;
 	unregister_pernet_subsys(&ip_vs_ftp_ops);
 	/* rcu_barrier() is called by netns */
 }