netfilter: quota2: add support to log quota limit reached.

This uses the NETLINK NETLINK_NFLOG family to log a single message
when the quota limit is reached.
It uses the same packet type as ipt_ULOG, but
 - never copies skb data,
 - uses 112 as the event number (ULOG's +1)

It doesn't log if the module param "event_num" is 0.

Change-Id: I6f31736b568bb31a4ff0b9ac2ee58380e6b675ca
Signed-off-by: JP Abgrall <jpa@google.com>

2 files changed, 104 insertions, 0 deletions

diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index ddb7bb507bd..5bd5c612a9b 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -975,6 +975,18 @@ config NETFILTER_XT_MATCH_QUOTA2
 	  If you want to compile it as a module, say M here and read
 	  <file:Documentation/kbuild/modules.txt>.  If unsure, say `N'.
 
+config NETFILTER_XT_MATCH_QUOTA2_LOG
+	bool '"quota2" Netfilter LOG support'
+	depends on NETFILTER_XT_MATCH_QUOTA2
+	depends on IP_NF_TARGET_ULOG=n    # not yes, not module, just no
+	default n
+	help
+	  This option allows `quota2' to log ONCE when a quota limit
+	  is passed. It logs via NETLINK using the NETLINK_NFLOG family.
+	  It logs similarly to how ipt_ULOG would without data.
+
+	  If unsure, say `N'.
+
 config NETFILTER_XT_MATCH_RATEEST
 	tristate '"rateest" match support'
 	depends on NETFILTER_ADVANCED
diff --git a/net/netfilter/xt_quota2.c b/net/netfilter/xt_quota2.c
index 454ce10c8cd..3c72bea2dd6 100644
--- a/net/netfilter/xt_quota2.c
+++ b/net/netfilter/xt_quota2.c
@@ -19,6 +19,9 @@
 
 #include <linux/netfilter/x_tables.h>
 #include <linux/netfilter/xt_quota2.h>
+#ifdef CONFIG_NETFILTER_XT_MATCH_QUOTA2_LOG
+#include <linux/netfilter_ipv4/ipt_ULOG.h>
+#endif
 
 /**
  * @lock:	lock to protect quota writers from each other
@@ -32,6 +35,16 @@ struct xt_quota_counter {
 	struct proc_dir_entry *procfs_entry;
 };
 
+#ifdef CONFIG_NETFILTER_XT_MATCH_QUOTA2_LOG
+/* Harald's favorite number +1 :D From ipt_ULOG.C */
+static int qlog_nl_event = 112;
+module_param_named(event_num, qlog_nl_event, uint, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(event_num,
+		 "Event number for NETLINK_NFLOG message. 0 disables log."
+		 "111 is what ipt_ULOG uses.");
+static struct sock *nflognl;
+#endif
+
 static LIST_HEAD(counter_list);
 static DEFINE_SPINLOCK(counter_list_lock);
 
@@ -43,6 +56,69 @@ module_param_named(perms, quota_list_perms, uint, S_IRUGO | S_IWUSR);
 module_param_named(uid, quota_list_uid, uint, S_IRUGO | S_IWUSR);
 module_param_named(gid, quota_list_gid, uint, S_IRUGO | S_IWUSR);
 
+
+#ifdef CONFIG_NETFILTER_XT_MATCH_QUOTA2_LOG
+static void quota2_log(unsigned int hooknum,
+		       const struct sk_buff *skb,
+		       const struct net_device *in,
+		       const struct net_device *out,
+		       const char *prefix)
+{
+	ulog_packet_msg_t *pm;
+	struct sk_buff *log_skb;
+	size_t size;
+	struct nlmsghdr *nlh;
+
+	if (!qlog_nl_event)
+		return;
+
+	size = NLMSG_SPACE(sizeof(*pm));
+	size = max(size, (size_t)NLMSG_GOODSIZE);
+	log_skb = alloc_skb(size, GFP_ATOMIC);
+	if (!log_skb) {
+		pr_err("xt_quota2: cannot alloc skb for logging\n");
+		return;
+	}
+
+	/* NLMSG_PUT() uses "goto nlmsg_failure" */
+	nlh = NLMSG_PUT(log_skb, /*pid*/0, /*seq*/0, qlog_nl_event,
+			sizeof(*pm));
+	pm = NLMSG_DATA(nlh);
+	if (skb->tstamp.tv64 == 0)
+		__net_timestamp((struct sk_buff *)skb);
+	pm->data_len = 0;
+	pm->hook = hooknum;
+	if (prefix != NULL)
+		strlcpy(pm->prefix, prefix, sizeof(pm->prefix));
+	else
+		*(pm->prefix) = '\0';
+	if (in)
+		strlcpy(pm->indev_name, in->name, sizeof(pm->indev_name));
+	else
+		pm->indev_name[0] = '\0';
+
+	if (out)
+		strlcpy(pm->outdev_name, out->name, sizeof(pm->outdev_name));
+	else
+		pm->outdev_name[0] = '\0';
+
+	NETLINK_CB(log_skb).dst_group = 1;
+	pr_debug("throwing 1 packets to netlink group 1\n");
+	netlink_broadcast(nflognl, log_skb, 0, 1, GFP_ATOMIC);
+
+nlmsg_failure:  /* Used within NLMSG_PUT() */
+	pr_debug("xt_quota2: error during NLMSG_PUT\n");
+}
+#else
+static void quota2_log(unsigned int hooknum,
+		       const struct sk_buff *skb,
+		       const struct net_device *in,
+		       const struct net_device *out,
+		       const char *prefix)
+{
+}
+#endif  /* if+else CONFIG_NETFILTER_XT_MATCH_QUOTA2_LOG */
+
 static int quota_proc_read(char *page, char **start, off_t offset,
                            int count, int *eof, void *data)
 {
@@ -226,6 +302,14 @@ quota_mt2(const struct sk_buff *skb, struct xt_action_param *par)
 				e->quota -= (q->flags & XT_QUOTA_PACKET) ? 1 : skb->len;
 			ret = !ret;
 		} else {
+			/* We are transitioning, log that fact. */
+			if (e->quota) {
+				quota2_log(par->hooknum,
+					   skb,
+					   par->in,
+					   par->out,
+					   q->name);
+			}
 			/* we do not allow even small packets from now on */
 			e->quota = 0;
 		}
@@ -262,6 +346,14 @@ static int __init quota_mt2_init(void)
 	int ret;
 	pr_debug("xt_quota2: init()");
 
+#ifdef CONFIG_NETFILTER_XT_MATCH_QUOTA2_LOG
+	nflognl = netlink_kernel_create(&init_net,
+					NETLINK_NFLOG, 1, NULL,
+					NULL, THIS_MODULE);
+	if (!nflognl)
+		return -ENOMEM;
+#endif
+
 	proc_xt_quota = proc_mkdir("xt_quota", init_net.proc_net);
 	if (proc_xt_quota == NULL)
 		return -EACCES;