netfilter: ipset: Hold module reference while requesting a module

BugLink: https://bugs.launchpad.net/bugs/2095283

[ Upstream commit 456f010bfaefde84d3390c755eedb1b0a5857c3c ]

User space may unload ip_set.ko while it is itself requesting a set type
backend module, leading to a kernel crash. The race condition may be
provoked by inserting an mdelay() right after the nfnl_unlock() call.

Fixes: a7b4f98 ("netfilter: ipset: IP set core support")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Acked-by: Jozsef Kadlecsik <kadlec@netfilter.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
CVE-2024-56637
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>

Author: Phil Sutter

net/netfilter/ipset/ip_set_core.c

@@ -104,14 +104,19 @@ find_set_type(const char *name, u8 family, u8 revision)
 static bool
 load_settype(const char *name)
 {
+	if (!try_module_get(THIS_MODULE))
+		return false;
+
 	nfnl_unlock(NFNL_SUBSYS_IPSET);
 	pr_debug("try to load ip_set_%s\n", name);
 	if (request_module("ip_set_%s", name) < 0) {
 		pr_warn("Can't find ip_set type %s\n", name);
 		nfnl_lock(NFNL_SUBSYS_IPSET);
+		module_put(THIS_MODULE);
 		return false;
 	}
 	nfnl_lock(NFNL_SUBSYS_IPSET);
+	module_put(THIS_MODULE);
 	return true;
 }