netfilter: sysctl support of logger choice

This patchs adds support of modification of the used logger via sysctl.
It can be used to change the logger to module that can not use the bind
operation (ipt_LOG and ipt_ULOG). For this purpose, it creates a
directory /proc/sys/net/netfilter/nf_log which contains a file
per-protocol. The content of the file is the name current logger (NONE if
not set) and a logger can be setup by simply echoing its name to the file.
By echoing "NONE" to a /proc/sys/net/netfilter/nf_log/PROTO file, the
logger corresponding to this PROTO is set to NULL.

Signed-off-by: Eric Leblond <eric@inl.fr>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/netfilter/nf_log.c

@@ -14,6 +14,7 @@
    LOG target modules */
 
 #define NF_LOG_PREFIXLEN		128
+#define NFLOGGER_NAME_LEN		64
 
 static const struct nf_logger *nf_loggers[NFPROTO_NUMPROTO] __read_mostly;
 static struct list_head nf_loggers_l[NFPROTO_NUMPROTO] __read_mostly;
@@ -207,18 +208,100 @@ static const struct file_operations nflog_file_ops = {
 	.release = seq_release,
 };
 
+
 #endif /* PROC_FS */
 
+#ifdef CONFIG_SYSCTL
+struct ctl_path nf_log_sysctl_path[] = {
+	{ .procname = "net", .ctl_name = CTL_NET, },
+	{ .procname = "netfilter", .ctl_name = NET_NETFILTER, },
+	{ .procname = "nf_log", .ctl_name = CTL_UNNUMBERED, },
+	{ }
+};
+
+static char nf_log_sysctl_fnames[NFPROTO_NUMPROTO-NFPROTO_UNSPEC][3];
+static struct ctl_table nf_log_sysctl_table[NFPROTO_NUMPROTO+1];
+static struct ctl_table_header *nf_log_dir_header;
+
+static int nf_log_proc_dostring(ctl_table *table, int write, struct file *filp,
+			 void *buffer, size_t *lenp, loff_t *ppos)
+{
+	const struct nf_logger *logger;
+	int r = 0;
+	int tindex = (unsigned long)table->extra1;
+
+	if (write) {
+		if (!strcmp(buffer, "NONE")) {
+			nf_log_unbind_pf(tindex);
+			return 0;
+		}
+		mutex_lock(&nf_log_mutex);
+		logger = __find_logger(tindex, buffer);
+		if (logger == NULL) {
+			mutex_unlock(&nf_log_mutex);
+			return -ENOENT;
+		}
+		rcu_assign_pointer(nf_loggers[tindex], logger);
+		mutex_unlock(&nf_log_mutex);
+	} else {
+		rcu_read_lock();
+		logger = rcu_dereference(nf_loggers[tindex]);
+		if (!logger)
+			table->data = "NONE";
+		else
+			table->data = logger->name;
+		r = proc_dostring(table, write, filp, buffer, lenp, ppos);
+		rcu_read_unlock();
+	}
+
+	return r;
+}
+
+static __init int netfilter_log_sysctl_init(void)
+{
+	int i;
+
+	for (i = NFPROTO_UNSPEC; i < NFPROTO_NUMPROTO; i++) {
+		snprintf(nf_log_sysctl_fnames[i-NFPROTO_UNSPEC], 3, "%d", i);
+		nf_log_sysctl_table[i].ctl_name	= CTL_UNNUMBERED;
+		nf_log_sysctl_table[i].procname	=
+			nf_log_sysctl_fnames[i-NFPROTO_UNSPEC];
+		nf_log_sysctl_table[i].data = NULL;
+		nf_log_sysctl_table[i].maxlen =
+			NFLOGGER_NAME_LEN * sizeof(char);
+		nf_log_sysctl_table[i].mode = 0644;
+		nf_log_sysctl_table[i].proc_handler = nf_log_proc_dostring;
+		nf_log_sysctl_table[i].extra1 = (void *)(unsigned long) i;
+	}
+
+	nf_log_dir_header = register_sysctl_paths(nf_log_sysctl_path,
+				       nf_log_sysctl_table);
+	if (!nf_log_dir_header)
+		return -ENOMEM;
+
+	return 0;
+}
+#else
+static __init int netfilter_log_sysctl_init(void)
+{
+	return 0;
+}
+#endif /* CONFIG_SYSCTL */
 
 int __init netfilter_log_init(void)
 {
-	int i;
+	int i, r;
 #ifdef CONFIG_PROC_FS
 	if (!proc_create("nf_log", S_IRUGO,
 			 proc_net_netfilter, &nflog_file_ops))
 		return -1;
 #endif
 
+	/* Errors will trigger panic, unroll on error is unnecessary. */
+	r = netfilter_log_sysctl_init();
+	if (r < 0)
+		return r;
+
 	for (i = NFPROTO_UNSPEC; i < NFPROTO_NUMPROTO; i++)
 		INIT_LIST_HEAD(&(nf_loggers_l[i]));