@@ -4,7 +4,7 @@
 #
 
 userprogs := bpfilter_umh
-bpfilter_umh-objs := main.o bflog.o io.o map-common.o context.o match.o target.o
+bpfilter_umh-objs := main.o bflog.o io.o map-common.o context.o match.o target.o rule.o
 userccflags += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi
 
 ifeq ($(CONFIG_BPFILTER_UMH), y)

@@ -0,0 +1,128 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2021 Telegram FZ-LLC
+ */
+
+#define _GNU_SOURCE
+
+#include "rule.h"
+
+#include "../../include/uapi/linux/bpfilter.h"
+
+#include <linux/err.h>
+
+#include <errno.h>
+#include <stdlib.h>
+
+#include "context.h"
+#include "bflog.h"
+
+static const struct bpfilter_ipt_target *
+ipt_entry_target(const struct bpfilter_ipt_entry *ipt_entry)
+{
+	return (const void *)ipt_entry + ipt_entry->target_offset;
+}
+
+static const struct bpfilter_ipt_match *ipt_entry_match(const struct bpfilter_ipt_entry *entry,
+							size_t offset)
+{
+	return (const void *)entry + offset;
+}
+
+static int ipt_entry_num_matches(const struct bpfilter_ipt_entry *ipt_entry)
+{
+	const struct bpfilter_ipt_match *ipt_match;
+	uint32_t offset = sizeof(*ipt_entry);
+	int num_matches = 0;
+
+	while (offset < ipt_entry->target_offset) {
+		ipt_match = ipt_entry_match(ipt_entry, offset);
+
+		if (ipt_entry->target_offset < offset + ipt_match->u.match_size)
+			return -EINVAL;
+
+		++num_matches;
+		offset += ipt_match->u.match_size;
+	}
+
+	if (offset != ipt_entry->target_offset)
+		return -EINVAL;
+
+	return num_matches;
+}
+
+static int check_ipt_entry_ip(struct context *ctx, const struct bpfilter_ipt_ip *ip)
+{
+	if (ip->flags & ~BPFILTER_IPT_F_MASK)
+		return -EINVAL;
+
+	if (ip->invflags & ~BPFILTER_IPT_INV_MASK)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int init_rule_matches(struct context *ctx, const struct bpfilter_ipt_entry *ipt_entry,
+			     struct rule *rule)
+{
+	const struct bpfilter_ipt_match *ipt_match;
+	uint32_t offset = sizeof(*ipt_entry);
+	struct match *match;
+	int err;
+
+	rule->matches = calloc(rule->num_matches, sizeof(rule->matches[0]));
+	if (!rule->matches)
+		return -ENOMEM;
+
+	match = rule->matches;
+	while (offset < ipt_entry->target_offset) {
+		ipt_match = ipt_entry_match(ipt_entry, offset);
+		err = init_match(ctx, ipt_match, match);
+		if (err)
+			return err;
+
+		++match;
+		offset += ipt_match->u.match_size;
+	}
+
+	return 0;
+}
+
+int init_rule(struct context *ctx, const struct bpfilter_ipt_entry *ipt_entry, struct rule *rule)
+{
+	const struct bpfilter_ipt_target *ipt_target;
+	int err;
+
+	err = check_ipt_entry_ip(ctx, &ipt_entry->ip);
+
+	if (ipt_entry->next_offset < ipt_entry->target_offset)
+		return -EINVAL;
+
+	if (ipt_entry->target_offset < sizeof(*ipt_entry))
+		return -EINVAL;
+
+	ipt_target = ipt_entry_target(ipt_entry);
+	if (ipt_target->u.target_size != ipt_entry->next_offset - ipt_entry->target_offset)
+		return -EINVAL;
+
+	err = init_target(ctx, ipt_target, &rule->target);
+	if (err)
+		return err;
+
+	rule->num_matches = ipt_entry_num_matches(ipt_entry);
+	if (rule->num_matches < 0)
+		return rule->num_matches;
+
+	err = init_rule_matches(ctx, ipt_entry, rule);
+	if (err) {
+		free_rule(rule);
+		return err;
+	}
+
+	return 0;
+}
+
+void free_rule(struct rule *rule)
+{
+	free(rule->matches);
+}

@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2021 Telegram FZ-LLC
+ */
+
+#ifndef NET_BPFILTER_RULE_H
+#define NET_BPFILTER_RULE_H
+
+#include <stdint.h>
+
+#include "target.h"
+
+struct bpfilter_ipt_entry;
+struct context;
+struct match;
+
+struct rule {
+	uint32_t offset;
+	uint16_t num_matches;
+	struct match *matches;
+	struct target target;
+};
+
+int init_rule(struct context *ctx, const struct bpfilter_ipt_entry *ipt_entry, struct rule *rule);
+void free_rule(struct rule *rule);
+
+#endif // NET_BPFILTER_RULE_H

@@ -3,3 +3,4 @@ test_io
 test_map
 test_match
 test_target
+test_rule

@@ -12,6 +12,7 @@ TEST_GEN_PROGS += test_io
 TEST_GEN_PROGS += test_map
 TEST_GEN_PROGS += test_match
 TEST_GEN_PROGS += test_target
+TEST_GEN_PROGS += test_rule
 
 KSFT_KHDR_INSTALL := 1
 

@@ -23,3 +24,6 @@ $(OUTPUT)/test_match: test_match.c $(BPFILTERSRCDIR)/match.c $(BPFILTERSRCDIR)/m
 	$(BPFILTERSRCDIR)/context.c $(BPFILTERSRCDIR)/bflog.c $(BPFILTERSRCDIR)/target.c
 $(OUTPUT)/test_target: test_target.c $(BPFILTERSRCDIR)/target.c $(BPFILTERSRCDIR)/map-common.c \
 	$(BPFILTERSRCDIR)/context.c $(BPFILTERSRCDIR)/bflog.c $(BPFILTERSRCDIR)/match.c
+$(OUTPUT)/test_rule: test_rule.c $(BPFILTERSRCDIR)/rule.c $(BPFILTERSRCDIR)/bflog.c 		\
+	$(BPFILTERSRCDIR)/map-common.c $(BPFILTERSRCDIR)/context.c $(BPFILTERSRCDIR)/match.c	\
+	$(BPFILTERSRCDIR)/target.c

@@ -7,6 +7,7 @@
 #include <linux/netfilter/x_tables.h>
 
 #include <stdio.h>
+#include <string.h>
 
 static inline void init_standard_target(struct xt_standard_target *ipt_target, int revision,
 					int verdict)

@@ -28,4 +29,11 @@ static inline void init_error_target(struct xt_error_target *ipt_target, int rev
 	snprintf(ipt_target->errorname, sizeof(ipt_target->errorname), "%s", error_name);
 }
 
+static inline void init_standard_entry(struct ipt_entry *entry, __u16 matches_size)
+{
+	memset(entry, 0, sizeof(*entry));
+	entry->target_offset = sizeof(*entry) + matches_size;
+	entry->next_offset = sizeof(*entry) + matches_size + sizeof(struct xt_standard_target);
+}
+
 #endif // BPFILTER_UTIL_H

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+
+#include "rule.h"
+
+#include <linux/bpfilter.h>
+#include <linux/err.h>
+
+#include <linux/netfilter_ipv4/ip_tables.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "../../kselftest_harness.h"
+
+#include "context.h"
+#include "rule.h"
+
+#include "bpfilter_util.h"
+
+FIXTURE(test_standard_rule)
+{
+	struct context ctx;
+	struct {
+		struct ipt_entry entry;
+		struct xt_standard_target target;
+	} entry;
+	struct rule rule;
+};
+
+FIXTURE_SETUP(test_standard_rule)
+{
+	const int verdict = BPFILTER_NF_ACCEPT;
+
+	ASSERT_EQ(create_context(&self->ctx), 0);
+	self->ctx.log_file = stderr;
+
+	init_standard_entry(&self->entry.entry, 0);
+	init_standard_target(&self->entry.target, 0, -verdict - 1);
+}
+
+FIXTURE_TEARDOWN(test_standard_rule)
+{
+	free_rule(&self->rule);
+	free_context(&self->ctx);
+}
+
+TEST_F(test_standard_rule, init)
+{
+	ASSERT_EQ(0, init_rule(&self->ctx, (const struct bpfilter_ipt_entry *)&self->entry.entry,
+			       &self->rule));
+}
+
+TEST_HARNESS_MAIN