netfilter: log: nf_log_packet() as real unified interface

Before this patch, the nf_loginfo parameter specified the logging
configuration in case the specified default logger was loaded. This
patch updates the semantics of the nf_loginfo parameter in
nf_log_packet() which now indicates the logger that you explicitly
want to use.

Thus, nf_log_packet() is exposed as an unified interface which
internally routes the log message to the corresponding logger type
by family.

The module dependencies are expressed by the new nf_logger_find_get()
and nf_logger_put() functions which bump the logger module refcount.
Thus, you can not remove logger modules that are used by rules anymore.

Another important effect of this change is that the family specific
module is only loaded when required. Therefore, xt_LOG and nft_log
will just trigger the autoload of the nf_log_{ip,ip6} modules
according to the family.

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

include/net/netfilter/nf_log.h

···
 		   const struct nf_logger *logger);
 void nf_log_unbind_pf(struct net *net, u_int8_t pf);
 
+int nf_logger_find_get(int pf, enum nf_log_type type);
+void nf_logger_put(int pf, enum nf_log_type type);
+
+#define MODULE_ALIAS_NF_LOGGER(family, type) \
+	MODULE_ALIAS("nf-logger-" __stringify(family) "-" __stringify(type))
+
 /* Calls the registered backend logging function */
 __printf(8, 9)
 void nf_log_packet(struct net *net,
···
 struct nf_log_buf *nf_log_buf_open(void);
 __printf(2, 3) int nf_log_buf_add(struct nf_log_buf *m, const char *f, ...);
 void nf_log_buf_close(struct nf_log_buf *m);
-
-void nf_log_ip_packet(struct net *net, u_int8_t pf,
-		      unsigned int hooknum, const struct sk_buff *skb,
-		      const struct net_device *in,
-		      const struct net_device *out,
-		      const struct nf_loginfo *loginfo,
-		      const char *prefix);
-
-void nf_log_ip6_packet(struct net *net, u_int8_t pf,
-		       unsigned int hooknum, const struct sk_buff *skb,
-		       const struct net_device *in,
-		       const struct net_device *out,
-		       const struct nf_loginfo *loginfo,
-		       const char *prefix);
 
 /* common logging functions */
 int nf_log_dump_udp_header(struct nf_log_buf *m, const struct sk_buff *skb,

net/ipv4/netfilter/nf_log_ipv4.c

···
 	nf_log_buf_add(m, " ");
 }
 
-void nf_log_ip_packet(struct net *net, u_int8_t pf,
-		      unsigned int hooknum, const struct sk_buff *skb,
-		      const struct net_device *in,
-		      const struct net_device *out,
-		      const struct nf_loginfo *loginfo,
-		      const char *prefix)
+static void nf_log_ip_packet(struct net *net, u_int8_t pf,
+			     unsigned int hooknum, const struct sk_buff *skb,
+			     const struct net_device *in,
+			     const struct net_device *out,
+			     const struct nf_loginfo *loginfo,
+			     const char *prefix)
 {
 	struct nf_log_buf *m;
 
···
 
 	nf_log_buf_close(m);
 }
-EXPORT_SYMBOL_GPL(nf_log_ip_packet);
 
 static struct nf_logger nf_ip_logger __read_mostly = {
 	.name		= "nf_log_ipv4",
···
 MODULE_AUTHOR("Netfilter Core Team <[e-mail]>");
 MODULE_DESCRIPTION("Netfilter IPv4 packet logging");
 MODULE_LICENSE("GPL");
+MODULE_ALIAS_NF_LOGGER(AF_INET, 0);

net/ipv6/netfilter/nf_log_ipv6.c

···
 	}
 }
 
-void nf_log_ip6_packet(struct net *net, u_int8_t pf,
-		       unsigned int hooknum, const struct sk_buff *skb,
-		       const struct net_device *in,
-		       const struct net_device *out,
-		       const struct nf_loginfo *loginfo,
-		       const char *prefix)
+static void nf_log_ip6_packet(struct net *net, u_int8_t pf,
+			      unsigned int hooknum, const struct sk_buff *skb,
+			      const struct net_device *in,
+			      const struct net_device *out,
+			      const struct nf_loginfo *loginfo,
+			      const char *prefix)
 {
 	struct nf_log_buf *m;
 
···
 
 	nf_log_buf_close(m);
 }
-EXPORT_SYMBOL_GPL(nf_log_ip6_packet);
 
 static struct nf_logger nf_ip6_logger __read_mostly = {
 	.name		= "nf_log_ipv6",
···
 MODULE_AUTHOR("Netfilter Core Team <[e-mail]>");
 MODULE_DESCRIPTION("Netfilter IPv4 packet logging");
 MODULE_LICENSE("GPL");
+MODULE_ALIAS_NF_LOGGER(AF_INET6, 0);

net/netfilter/nf_log.c

···
 }
 EXPORT_SYMBOL(nf_log_unbind_pf);
 
+int nf_logger_find_get(int pf, enum nf_log_type type)
+{
+	struct nf_logger *logger;
+	int ret = -ENOENT;
+
+	logger = loggers[pf][type];
+	if (logger == NULL)
+		request_module("nf-logger-%u-%u", pf, type);
+
+	rcu_read_lock();
+	logger = rcu_dereference(loggers[pf][type]);
+	if (logger == NULL)
+		goto out;
+
+	if (logger && try_module_get(logger->me))
+		ret = 0;
+out:
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL_GPL(nf_logger_find_get);
+
+void nf_logger_put(int pf, enum nf_log_type type)
+{
+	struct nf_logger *logger;
+
+	BUG_ON(loggers[pf][type] == NULL);
+
+	rcu_read_lock();
+	logger = rcu_dereference(loggers[pf][type]);
+	module_put(logger->me);
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(nf_logger_put);
+
 void nf_log_packet(struct net *net,
 		   u_int8_t pf,
 		   unsigned int hooknum,
···
 	const struct nf_logger *logger;
 
 	rcu_read_lock();
-	logger = rcu_dereference(net->nf.nf_loggers[pf]);
+	if (loginfo != NULL)
+		logger = rcu_dereference(loggers[pf][loginfo->type]);
+	else
+		logger = rcu_dereference(net->nf.nf_loggers[pf]);
+
 	if (logger) {
 		va_start(args, fmt);
 		vsnprintf(prefix, sizeof(prefix), fmt, args);

net/netfilter/nfnetlink_log.c

···
 MODULE_AUTHOR("Harald Welte <[e-mail]>");
 MODULE_LICENSE("GPL");
 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_ULOG);
+MODULE_ALIAS_NF_LOGGER(AF_INET, 1);
+MODULE_ALIAS_NF_LOGGER(AF_INET6, 1);
+MODULE_ALIAS_NF_LOGGER(AF_BRIDGE, 1);
 
 module_init(nfnetlink_log_init);
 module_exit(nfnetlink_log_fini);

net/netfilter/xt_LOG.c

···
 	li.u.log.level = loginfo->level;
 	li.u.log.logflags = loginfo->logflags;
 
-	if (par->family == NFPROTO_IPV4)
-		nf_log_ip_packet(net, NFPROTO_IPV4, par->hooknum, skb, par->in,
-			         par->out, &li, loginfo->prefix);
-#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
-	else if (par->family == NFPROTO_IPV6)
-		nf_log_ip6_packet(net, NFPROTO_IPV6, par->hooknum, skb, par->in,
-				  par->out, &li, loginfo->prefix);
-#endif
-	else
-		WARN_ON_ONCE(1);
-
+	nf_log_packet(net, par->family, par->hooknum, skb, par->in, par->out,
+		      &li, loginfo->prefix);
 	return XT_CONTINUE;
 }
 
···
 		return -EINVAL;
 	}
 
-	return 0;
+	return nf_logger_find_get(par->family, NF_LOG_TYPE_LOG);
+}
+
+static void log_tg_destroy(const struct xt_tgdtor_param *par)
+{
+	nf_logger_put(par->family, NF_LOG_TYPE_LOG);
 }
 
 static struct xt_target log_tg_regs[] __read_mostly = {
···
 		.target		= log_tg,
 		.targetsize	= sizeof(struct xt_log_info),
 		.checkentry	= log_tg_check,
+		.destroy	= log_tg_destroy,
 		.me		= THIS_MODULE,
 	},
 #if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
···
 		.target		= log_tg,
 		.targetsize	= sizeof(struct xt_log_info),
 		.checkentry	= log_tg_check,
+		.destroy	= log_tg_destroy,
 		.me		= THIS_MODULE,
 	},
 #endif