[NETFILTER]: x_tables: add TRACE target

The TRACE target can be used to follow IP and IPv6 packets through
the ruleset.

Signed-off-by: Jozsef Kadlecsik <[e-mail]>
Signed-off-by: Patrick NcHardy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/skbuff.h

···
  *	@mark: Generic packet mark
  *	@nfct: Associated connection, if any
  *	@ipvs_property: skbuff is owned by ipvs
+ *	@nf_trace: netfilter packet trace flag
  *	@nfctinfo: Relationship of this skb to the connection
  *	@nfct_reasm: netfilter conntrack re-assembly pointer
  *	@nf_bridge: Saved data about a bridged frame - see br_netfilter.c
···
 				nfctinfo:3;
 	__u8			pkt_type:3,
 				fclone:2,
-				ipvs_property:1;
+				ipvs_property:1,
+				nf_trace:1;
 	__be16			protocol;
 
 	void			(*destructor)(struct sk_buff *skb);

net/core/skbuff.c

···
 	n->destructor = NULL;
 	C(mark);
 	__nf_copy(n, skb);
+#if defined(CONFIG_NETFILTER_XT_TARGET_TRACE) || \
+    defined(CONFIG_NETFILTER_XT_TARGET_TRACE_MODULE)
+	C(nf_trace);
+#endif
 #ifdef CONFIG_NET_SCHED
 	C(tc_index);
 #ifdef CONFIG_NET_CLS_ACT
···
 	new->destructor = NULL;
 	new->mark	= old->mark;
 	__nf_copy(new, old);
+#if defined(CONFIG_NETFILTER_XT_TARGET_TRACE) || \
+    defined(CONFIG_NETFILTER_XT_TARGET_TRACE_MODULE)
+	new->nf_trace	= old->nf_trace;
+#endif
 #if defined(CONFIG_IP_VS) || defined(CONFIG_IP_VS_MODULE)
 	new->ipvs_property = old->ipvs_property;
 #endif

net/ipv4/ip_output.c

···
 	to->tc_index = from->tc_index;
 #endif
 	nf_copy(to, from);
+#if defined(CONFIG_NETFILTER_XT_TARGET_TRACE) || \
+    defined(CONFIG_NETFILTER_XT_TARGET_TRACE_MODULE)
+	to->nf_trace = from->nf_trace;
+#endif
 #if defined(CONFIG_IP_VS) || defined(CONFIG_IP_VS_MODULE)
 	to->ipvs_property = from->ipvs_property;
 #endif

net/ipv4/netfilter/ip_tables.c

···
 	return (struct ipt_entry *)(base + offset);
 }
 
+/* All zeroes == unconditional rule. */
+static inline int
+unconditional(const struct ipt_ip *ip)
+{
+	unsigned int i;
+
+	for (i = 0; i < sizeof(*ip)/sizeof(__u32); i++)
+		if (((__u32 *)ip)[i])
+			return 0;
+
+	return 1;
+}
+
+#if defined(CONFIG_NETFILTER_XT_TARGET_TRACE) || \
+    defined(CONFIG_NETFILTER_XT_TARGET_TRACE_MODULE)
+static const char *hooknames[] = {
+	[NF_IP_PRE_ROUTING]		= "PREROUTING",
+	[NF_IP_LOCAL_IN]		= "INPUT",
+	[NF_IP_FORWARD]			= "FORWARD",
+	[NF_IP_LOCAL_OUT]		= "OUTPUT",
+	[NF_IP_POST_ROUTING]		= "POSTROUTING",
+};
+
+enum nf_ip_trace_comments {
+	NF_IP_TRACE_COMMENT_RULE,
+	NF_IP_TRACE_COMMENT_RETURN,
+	NF_IP_TRACE_COMMENT_POLICY,
+};
+
+static const char *comments[] = {
+	[NF_IP_TRACE_COMMENT_RULE]	= "rule",
+	[NF_IP_TRACE_COMMENT_RETURN]	= "return",
+	[NF_IP_TRACE_COMMENT_POLICY]	= "policy",
+};
+
+static struct nf_loginfo trace_loginfo = {
+	.type = NF_LOG_TYPE_LOG,
+	.u = {
+		.log = {
+			.level = 4,
+			.logflags = NF_LOG_MASK,
+		},
+	},
+};
+
+static inline int
+get_chainname_rulenum(struct ipt_entry *s, struct ipt_entry *e,
+		      char *hookname, char **chainname,
+		      char **comment, unsigned int *rulenum)
+{
+	struct ipt_standard_target *t = (void *)ipt_get_target(s);
+
+	if (strcmp(t->target.u.kernel.target->name, IPT_ERROR_TARGET) == 0) {
+		/* Head of user chain: ERROR target with chainname */
+		*chainname = t->target.data;
+		(*rulenum) = 0;
+	} else if (s == e) {
+		(*rulenum)++;
+
+		if (s->target_offset == sizeof(struct ipt_entry)
+		   && strcmp(t->target.u.kernel.target->name,
+			     IPT_STANDARD_TARGET) == 0
+		   && t->verdict < 0
+		   && unconditional(&s->ip)) {
+			/* Tail of chains: STANDARD target (return/policy) */
+			*comment = *chainname == hookname
+				? (char *)comments[NF_IP_TRACE_COMMENT_POLICY]
+				: (char *)comments[NF_IP_TRACE_COMMENT_RETURN];
+		}
+		return 1;
+	} else
+		(*rulenum)++;
+
+	return 0;
+}
+
+static void trace_packet(struct sk_buff *skb,
+			 unsigned int hook,
+			 const struct net_device *in,
+			 const struct net_device *out,
+			 char *tablename,
+			 struct xt_table_info *private,
+			 struct ipt_entry *e)
+{
+	void *table_base;
+	struct ipt_entry *root;
+	char *hookname, *chainname, *comment;
+	unsigned int rulenum = 0;
+
+	table_base = (void *)private->entries[smp_processor_id()];
+	root = get_entry(table_base, private->hook_entry[hook]);
+
+	hookname = chainname = (char *)hooknames[hook];
+	comment = (char *)comments[NF_IP_TRACE_COMMENT_RULE];
+
+	IPT_ENTRY_ITERATE(root,
+			  private->size - private->hook_entry[hook],
+			  get_chainname_rulenum,
+			  e, hookname, &chainname, &comment, &rulenum);
+
+	nf_log_packet(AF_INET, hook, skb, in, out, &trace_loginfo,
+		      "TRACE: %s:%s:%s:%u ",
+		      tablename, chainname, comment, rulenum);
+}
+#endif
+
 /* Returns one of the generic firewall policies, like NF_ACCEPT. */
 unsigned int
 ipt_do_table(struct sk_buff **pskb,
···
 
 			t = ipt_get_target(e);
 			IP_NF_ASSERT(t->u.kernel.target);
+
+#if defined(CONFIG_NETFILTER_XT_TARGET_TRACE) || \
+    defined(CONFIG_NETFILTER_XT_TARGET_TRACE_MODULE)
+			/* The packet is traced: log it */
+			if (unlikely((*pskb)->nf_trace))
+				trace_packet(*pskb, hook, in, out,
+					     table->name, private, e);
+#endif
 			/* Standard target? */
 			if (!t->u.kernel.target->target) {
 				int v;
···
 		return NF_DROP;
 	else return verdict;
 #endif
-}
-
-/* All zeroes == unconditional rule. */
-static inline int
-unconditional(const struct ipt_ip *ip)
-{
-	unsigned int i;
-
-	for (i = 0; i < sizeof(*ip)/sizeof(__u32); i++)
-		if (((__u32 *)ip)[i])
-			return 0;
-
-	return 1;
 }
 
 /* Figures out from what hook each rule can be called: returns 0 if

net/ipv6/ip6_output.c

···
 	to->tc_index = from->tc_index;
 #endif
 	nf_copy(to, from);
+#if defined(CONFIG_NETFILTER_XT_TARGET_TRACE) || \
+    defined(CONFIG_NETFILTER_XT_TARGET_TRACE_MODULE)
+	to->nf_trace = from->nf_trace;
+#endif
 	skb_copy_secmark(to, from);
 }
 

net/ipv6/netfilter/ip6_tables.c

···
 	return (struct ip6t_entry *)(base + offset);
 }
 
+/* All zeroes == unconditional rule. */
+static inline int
+unconditional(const struct ip6t_ip6 *ipv6)
+{
+	unsigned int i;
+
+	for (i = 0; i < sizeof(*ipv6); i++)
+		if (((char *)ipv6)[i])
+			break;
+
+	return (i == sizeof(*ipv6));
+}
+
+#if defined(CONFIG_NETFILTER_XT_TARGET_TRACE) || \
+    defined(CONFIG_NETFILTER_XT_TARGET_TRACE_MODULE)
+/* This cries for unification! */
+static const char *hooknames[] = {
+	[NF_IP6_PRE_ROUTING]		= "PREROUTING",
+	[NF_IP6_LOCAL_IN]		= "INPUT",
+	[NF_IP6_FORWARD]		= "FORWARD",
+	[NF_IP6_LOCAL_OUT]		= "OUTPUT",
+	[NF_IP6_POST_ROUTING]		= "POSTROUTING",
+};
+
+enum nf_ip_trace_comments {
+	NF_IP6_TRACE_COMMENT_RULE,
+	NF_IP6_TRACE_COMMENT_RETURN,
+	NF_IP6_TRACE_COMMENT_POLICY,
+};
+
+static const char *comments[] = {
+	[NF_IP6_TRACE_COMMENT_RULE]	= "rule",
+	[NF_IP6_TRACE_COMMENT_RETURN]	= "return",
+	[NF_IP6_TRACE_COMMENT_POLICY]	= "policy",
+};
+
+static struct nf_loginfo trace_loginfo = {
+	.type = NF_LOG_TYPE_LOG,
+	.u = {
+		.log = {
+			.level = 4,
+			.logflags = NF_LOG_MASK,
+		},
+	},
+};
+
+static inline int
+get_chainname_rulenum(struct ip6t_entry *s, struct ip6t_entry *e,
+		      char *hookname, char **chainname,
+		      char **comment, unsigned int *rulenum)
+{
+	struct ip6t_standard_target *t = (void *)ip6t_get_target(s);
+
+	if (strcmp(t->target.u.kernel.target->name, IP6T_ERROR_TARGET) == 0) {
+		/* Head of user chain: ERROR target with chainname */
+		*chainname = t->target.data;
+		(*rulenum) = 0;
+	} else if (s == e) {
+		(*rulenum)++;
+
+		if (s->target_offset == sizeof(struct ip6t_entry)
+		   && strcmp(t->target.u.kernel.target->name,
+			     IP6T_STANDARD_TARGET) == 0
+		   && t->verdict < 0
+		   && unconditional(&s->ipv6)) {
+			/* Tail of chains: STANDARD target (return/policy) */
+			*comment = *chainname == hookname
+				? (char *)comments[NF_IP6_TRACE_COMMENT_POLICY]
+				: (char *)comments[NF_IP6_TRACE_COMMENT_RETURN];
+		}
+		return 1;
+	} else
+		(*rulenum)++;
+
+	return 0;
+}
+
+static void trace_packet(struct sk_buff *skb,
+			 unsigned int hook,
+			 const struct net_device *in,
+			 const struct net_device *out,
+			 char *tablename,
+			 struct xt_table_info *private,
+			 struct ip6t_entry *e)
+{
+	void *table_base;
+	struct ip6t_entry *root;
+	char *hookname, *chainname, *comment;
+	unsigned int rulenum = 0;
+
+	table_base = (void *)private->entries[smp_processor_id()];
+	root = get_entry(table_base, private->hook_entry[hook]);
+
+	hookname = chainname = (char *)hooknames[hook];
+	comment = (char *)comments[NF_IP6_TRACE_COMMENT_RULE];
+
+	IP6T_ENTRY_ITERATE(root,
+			   private->size - private->hook_entry[hook],
+			   get_chainname_rulenum,
+			   e, hookname, &chainname, &comment, &rulenum);
+
+	nf_log_packet(AF_INET6, hook, skb, in, out, &trace_loginfo,
+		      "TRACE: %s:%s:%s:%u ",
+		      tablename, chainname, comment, rulenum);
+}
+#endif
+
 /* Returns one of the generic firewall policies, like NF_ACCEPT. */
 unsigned int
 ip6t_do_table(struct sk_buff **pskb,
···
 
 			t = ip6t_get_target(e);
 			IP_NF_ASSERT(t->u.kernel.target);
+
+#if defined(CONFIG_NETFILTER_XT_TARGET_TRACE) || \
+    defined(CONFIG_NETFILTER_XT_TARGET_TRACE_MODULE)
+			/* The packet is traced: log it */
+			if (unlikely((*pskb)->nf_trace))
+				trace_packet(*pskb, hook, in, out,
+					     table->name, private, e);
+#endif
 			/* Standard target? */
 			if (!t->u.kernel.target->target) {
 				int v;
···
 		return NF_DROP;
 	else return verdict;
 #endif
-}
-
-/* All zeroes == unconditional rule. */
-static inline int
-unconditional(const struct ip6t_ip6 *ipv6)
-{
-	unsigned int i;
-
-	for (i = 0; i < sizeof(*ipv6); i++)
-		if (((char *)ipv6)[i])
-			break;
-
-	return (i == sizeof(*ipv6));
 }
 
 /* Figures out from what hook each rule can be called: returns 0 if

net/netfilter/Kconfig

···
 	  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_TARGET_TRACE
+	tristate  '"TRACE" target support'
+	depends on NETFILTER_XTABLES
+	depends on IP_NF_RAW || IP6_NF_RAW
+	help
+	  The TRACE target allows you to mark packets so that the kernel
+	  will log every rule which match the packets as those traverse
+	  the tables, chains, rules.
+
+	  If you want to compile it as a module, say M here and read
+	  <file:Documentation/modules.txt>.  If unsure, say `N'.
+
 config NETFILTER_XT_TARGET_SECMARK
 	tristate '"SECMARK" target support'
 	depends on NETFILTER_XTABLES && NETWORK_SECMARK

net/netfilter/Makefile

···
 obj-$(CONFIG_NETFILTER_XT_TARGET_NFQUEUE) += xt_NFQUEUE.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_NFLOG) += xt_NFLOG.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_NOTRACK) += xt_NOTRACK.o
+obj-$(CONFIG_NETFILTER_XT_TARGET_TRACE) += xt_TRACE.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_SECMARK) += xt_SECMARK.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_TCPMSS) += xt_TCPMSS.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_CONNSECMARK) += xt_CONNSECMARK.o

net/netfilter/xt_TRACE.c

···
+/* This is a module which is used to mark packets for tracing.
+ */
+#include <linux/module.h>
+#include <linux/skbuff.h>
+
+#include <linux/netfilter/x_tables.h>
+
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ipt_TRACE");
+MODULE_ALIAS("ip6t_TRACE");
+
+static unsigned int
+target(struct sk_buff **pskb,
+       const struct net_device *in,
+       const struct net_device *out,
+       unsigned int hooknum,
+       const struct xt_target *target,
+       const void *targinfo)
+{
+	(*pskb)->nf_trace = 1;
+	return XT_CONTINUE;
+}
+
+static struct xt_target xt_trace_target[] = {
+	{
+		.name		= "TRACE",
+		.family		= AF_INET,
+		.target		= target,
+		.table		= "raw",
+		.me		= THIS_MODULE,
+	},
+	{
+		.name		= "TRACE",
+		.family		= AF_INET6,
+		.target		= target,
+		.table		= "raw",
+		.me		= THIS_MODULE,
+	},
+};
+
+static int __init xt_trace_init(void)
+{
+	return xt_register_targets(xt_trace_target,
+				   ARRAY_SIZE(xt_trace_target));
+}
+
+static void __exit xt_trace_fini(void)
+{
+	xt_unregister_targets(xt_trace_target, ARRAY_SIZE(xt_trace_target));
+}
+
+module_init(xt_trace_init);
+module_exit(xt_trace_fini);