netfilter: log: protect nf_log_register against double registering

Currently, despite the comment right before the function,
nf_log_register allows registering two loggers on with the same type and
end up overwriting the previous register.

Not a real issue today as current tree doesn't have two loggers for the
same type but it's better to get this protected.

Also make sure that all of its callers do error checking.

Signed-off-by: Marcelo Ricardo Leitner <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/ipv4/netfilter/nf_log_arp.c

···
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/module.h>
 #include <linux/spinlock.h>
···
 	if (ret < 0)
 		return ret;
 
-	nf_log_register(NFPROTO_ARP, &nf_arp_logger);
+	ret = nf_log_register(NFPROTO_ARP, &nf_arp_logger);
+	if (ret < 0) {
+		pr_err("failed to register logger\n");
+		goto err1;
+	}
+
 	return 0;
+
+err1:
+	unregister_pernet_subsys(&nf_log_arp_net_ops);
+	return ret;
 }
 
 static void __exit nf_log_arp_exit(void)

net/ipv4/netfilter/nf_log_ipv4.c

···
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/module.h>
 #include <linux/spinlock.h>
···
 	if (ret < 0)
 		return ret;
 
-	nf_log_register(NFPROTO_IPV4, &nf_ip_logger);
+	ret = nf_log_register(NFPROTO_IPV4, &nf_ip_logger);
+	if (ret < 0) {
+		pr_err("failed to register logger\n");
+		goto err1;
+	}
+
 	return 0;
+
+err1:
+	unregister_pernet_subsys(&nf_log_ipv4_net_ops);
+	return ret;
 }
 
 static void __exit nf_log_ipv4_exit(void)

net/ipv6/netfilter/nf_log_ipv6.c

···
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/module.h>
 #include <linux/spinlock.h>
···
 	if (ret < 0)
 		return ret;
 
-	nf_log_register(NFPROTO_IPV6, &nf_ip6_logger);
+	ret = nf_log_register(NFPROTO_IPV6, &nf_ip6_logger);
+	if (ret < 0) {
+		pr_err("failed to register logger\n");
+		goto err1;
+	}
+
 	return 0;
+
+err1:
+	unregister_pernet_subsys(&nf_log_ipv6_net_ops);
+	return ret;
 }
 
 static void __exit nf_log_ipv6_exit(void)

net/netfilter/nf_log.c

···
 int nf_log_register(u_int8_t pf, struct nf_logger *logger)
 {
 	int i;
+	int ret = 0;
 
 	if (pf >= ARRAY_SIZE(init_net.nf.nf_loggers))
 		return -EINVAL;
···
 	mutex_lock(&nf_log_mutex);
 
 	if (pf == NFPROTO_UNSPEC) {
+		for (i = NFPROTO_UNSPEC; i < NFPROTO_NUMPROTO; i++) {
+			if (rcu_access_pointer(loggers[i][logger->type])) {
+				ret = -EEXIST;
+				goto unlock;
+			}
+		}
 		for (i = NFPROTO_UNSPEC; i < NFPROTO_NUMPROTO; i++)
 			rcu_assign_pointer(loggers[i][logger->type], logger);
 	} else {
-		/* register at end of list to honor first register win */
+		if (rcu_access_pointer(loggers[pf][logger->type])) {
+			ret = -EEXIST;
+			goto unlock;
+		}
 		rcu_assign_pointer(loggers[pf][logger->type], logger);
 	}
 
+unlock:
 	mutex_unlock(&nf_log_mutex);
-
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL(nf_log_register);