packet-solutions: extract solutions to separate files

In order to split solutions for different lessons we move XDP code to
individual files.  This commit creates files containing solutions for the
packet03-redirecting and packet02-rewriting lessons.

In particular, add a solution for the first assignment of the packet-02 lesson:
rewrite UDP and TCP ports for incoming packets.

The packet01-parsing is pretty simple and examples of using parsing functions
can be found in all consequent examples.

Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>

Author: aspsk

common/parsing_helpers.h

@@ -26,6 +26,8 @@
 #include <linux/ipv6.h>
 #include <linux/icmp.h>
 #include <linux/icmpv6.h>
+#include <linux/udp.h>
+#include <linux/tcp.h>
 
 /* Header cursor to keep track of current parsing position */
 struct hdr_cursor {
@@ -185,4 +187,50 @@ static __always_inline int parse_icmphdr_common(struct hdr_cursor *nh,
 	return h->type;
 }
 
+/*
+ * parse_tcphdr: parse the udp header and return the length of the udp payload
+ */
+static __always_inline int parse_udphdr(struct hdr_cursor *nh,
+					void *data_end,
+					struct udphdr **udphdr)
+{
+	int len;
+	struct udphdr *h = nh->pos;
+
+	if (h + 1 > data_end)
+		return -1;
+
+	nh->pos  = h + 1;
+	*udphdr = h;
+
+	len = bpf_ntohs(h->len) - sizeof(struct udphdr);
+	if (len < 0)
+		return -1;
+
+	return len;
+}
+
+/*
+ * parse_tcphdr: parse and return the length of the tcp header
+ */
+static __always_inline int parse_tcphdr(struct hdr_cursor *nh,
+					void *data_end,
+					struct tcphdr **tcphdr)
+{
+	int len;
+	struct tcphdr *h = nh->pos;
+
+	if (h + 1 > data_end)
+		return -1;
+
+	len = h->doff * 4;
+	if ((void *) h + len > data_end)
+		return -1;
+
+	nh->pos  = h + 1;
+	*tcphdr = h;
+
+	return len;
+}
+
 #endif /* __PARSING_HELPERS_H */

packet-solutions/Makefile

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
 
-XDP_TARGETS  := xdp_prog_kern
+XDP_TARGETS  := xdp_prog_kern_02 xdp_prog_kern_03
 USER_TARGETS := xdp_prog_user
 
 LIBBPF_DIR = ../libbpf/src/

packet-solutions/xdp_prog_kern_02.c

@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/bpf.h>
+#include <linux/in.h>
+#include "bpf_helpers.h"
+#include "bpf_endian.h"
+
+// The parsing helper functions from the packet01 lesson have moved here
+#include "../common/parsing_helpers.h"
+#include "../common/rewrite_helpers.h"
+
+/* Defines xdp_stats_map */
+#include "../common/xdp_stats_kern_user.h"
+#include "../common/xdp_stats_kern.h"
+
+/*
+ * Solution to the assignment 1 in lesson packet02
+ */
+SEC("xdp_patch_ports")
+int xdp_patch_ports_func(struct xdp_md *ctx)
+{
+	int action = XDP_PASS;
+	int eth_type, ip_type;
+	struct ethhdr *eth;
+	struct iphdr *iphdr;
+	struct ipv6hdr *ipv6hdr;
+	struct udphdr *udphdr;
+	struct tcphdr *tcphdr;
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	struct hdr_cursor nh = { .pos = data };
+
+	eth_type = parse_ethhdr(&nh, data_end, &eth);
+	if (eth_type < 0) {
+		action = XDP_ABORTED;
+		goto out;
+	}
+
+	if (eth_type == ETH_P_IP) {
+		ip_type = parse_iphdr(&nh, data_end, &iphdr);
+	} else if (eth_type == ETH_P_IPV6) {
+		ip_type = parse_ip6hdr(&nh, data_end, &ipv6hdr);
+	} else {
+		goto out;
+	}
+
+	if (ip_type == IPPROTO_UDP) {
+		if (parse_udphdr(&nh, data_end, &udphdr) < 0) {
+			action = XDP_ABORTED;
+			goto out;
+		}
+		udphdr->dest = bpf_htons(bpf_ntohs(udphdr->dest) - 1);
+	} else if (ip_type == IPPROTO_TCP) {
+		if (parse_tcphdr(&nh, data_end, &tcphdr) < 0) {
+			action = XDP_ABORTED;
+			goto out;
+		}
+		tcphdr->dest = bpf_htons(bpf_ntohs(tcphdr->dest) - 1);
+	}
+
+out:
+	return xdp_stats_record_action(ctx, action);
+}
+
+/*
+ * Solution to the assignments 2 and 3 in lesson packet02: Will pop outermost
+ * VLAN tag if it exists, otherwise push a new one with ID 1
+ */
+SEC("xdp_vlan_swap")
+int xdp_vlan_swap_func(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+
+	/* These keep track of the next header type and iterator pointer */
+	struct hdr_cursor nh;
+	int nh_type;
+	nh.pos = data;
+
+	struct ethhdr *eth;
+	nh_type = parse_ethhdr(&nh, data_end, &eth);
+	if (nh_type < 0)
+		return XDP_PASS;
+
+	if (proto_is_vlan(eth->h_proto))
+		vlan_tag_pop(ctx, eth);
+	else
+		vlan_tag_push(ctx, eth, 1);
+
+	return XDP_PASS;
+}
+
+SEC("xdp_pass")
+int xdp_pass_func(struct xdp_md *ctx)
+{
+	return XDP_PASS;
+}
+
+char _license[] SEC("license") = "GPL";

packet-solutions/xdp_prog_kern.c renamed to packet-solutions/xdp_prog_kern_03.c

@@ -30,33 +30,6 @@ struct bpf_map_def SEC("maps") redirect_params = {
 	.max_entries = 1,
 };
 
-/* Solution to the assignments in lesson packet02: Will pop outermost VLAN tag
- * if it exists, otherwise push a new one with ID 1
- */
-SEC("xdp_vlan_swap")
-int xdp_vlan_swap_func(struct xdp_md *ctx)
-{
-	void *data_end = (void *)(long)ctx->data_end;
-	void *data = (void *)(long)ctx->data;
-
-        /* These keep track of the next header type and iterator pointer */
-	struct hdr_cursor nh;
-	int nh_type;
-        nh.pos = data;
-
-	struct ethhdr *eth;
-	nh_type = parse_ethhdr(&nh, data_end, &eth);
-        if (nh_type < 0)
-                return XDP_PASS;
-
-        if (proto_is_vlan(eth->h_proto))
-                vlan_tag_pop(ctx, eth);
-        else
-                vlan_tag_push(ctx, eth, 1);
-
-        return XDP_PASS;
-}
-
 static __always_inline __u16 csum_fold_helper(__u32 csum)
 {
 	return ~((csum & 0xffff) + (csum >> 16));
@@ -172,7 +145,7 @@ int xdp_icmp_echo_func(struct xdp_md *ctx)
 	return xdp_stats_record_action(ctx, action);
 }
 
-/* Assignment 2 */
+/* Solution to packet03/assignment-2 */
 SEC("xdp_redirect")
 int xdp_redirect_func(struct xdp_md *ctx)
 {
@@ -201,7 +174,7 @@ int xdp_redirect_func(struct xdp_md *ctx)
 	return xdp_stats_record_action(ctx, action);
 }
 
-/* Assignment 3 */
+/* Solution to packet03/assignment-3 */
 SEC("xdp_redirect_map")
 int xdp_redirect_map_func(struct xdp_md *ctx)
 {