From 05e59e5fb0064c97a1c10921ecd549f2d4a58565 Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Wed, 09 Oct 2024 06:14:40 +0000
Subject: [PATCH] add REDIRECT
---
kernel/samples/bpf/xdp_fwd_kern.c | 50 +++++++++++++++++++++++++++++++++++---------------
1 files changed, 35 insertions(+), 15 deletions(-)
diff --git a/kernel/samples/bpf/xdp_fwd_kern.c b/kernel/samples/bpf/xdp_fwd_kern.c
index a7e94e7..54c099c 100644
--- a/kernel/samples/bpf/xdp_fwd_kern.c
+++ b/kernel/samples/bpf/xdp_fwd_kern.c
@@ -19,16 +19,16 @@
#include <linux/ip.h>
#include <linux/ipv6.h>
-#include "bpf_helpers.h"
+#include <bpf/bpf_helpers.h>
#define IPV6_FLOWINFO_MASK cpu_to_be32(0x0FFFFFFF)
-struct bpf_map_def SEC("maps") tx_port = {
- .type = BPF_MAP_TYPE_DEVMAP,
- .key_size = sizeof(int),
- .value_size = sizeof(int),
- .max_entries = 64,
-};
+struct {
+ __uint(type, BPF_MAP_TYPE_DEVMAP);
+ __uint(key_size, sizeof(int));
+ __uint(value_size, sizeof(int));
+ __uint(max_entries, 64);
+} xdp_tx_ports SEC(".maps");
/* from include/net/ip.h */
static __always_inline int ip_decrease_ttl(struct iphdr *iph)
@@ -102,14 +102,34 @@
fib_params.ifindex = ctx->ingress_ifindex;
rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags);
-
- /* verify egress index has xdp support
- * TO-DO bpf_map_lookup_elem(&tx_port, &key) fails with
- * cannot pass map_type 14 into func bpf_map_lookup_elem#1:
- * NOTE: without verification that egress index supports XDP
- * forwarding packets are dropped.
+ /*
+ * Some rc (return codes) from bpf_fib_lookup() are important,
+ * to understand how this XDP-prog interacts with network stack.
+ *
+ * BPF_FIB_LKUP_RET_NO_NEIGH:
+ * Even if route lookup was a success, then the MAC-addresses are also
+ * needed. This is obtained from arp/neighbour table, but if table is
+ * (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned. To avoid
+ * doing ARP lookup directly from XDP, then send packet to normal
+ * network stack via XDP_PASS and expect it will do ARP resolution.
+ *
+ * BPF_FIB_LKUP_RET_FWD_DISABLED:
+ * The bpf_fib_lookup respect sysctl net.ipv{4,6}.conf.all.forwarding
+ * setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not
+ * enabled this on ingress device.
*/
- if (rc == 0) {
+ if (rc == BPF_FIB_LKUP_RET_SUCCESS) {
+ /* Verify egress index has been configured as TX-port.
+ * (Note: User can still have inserted an egress ifindex that
+ * doesn't support XDP xmit, which will result in packet drops).
+ *
+ * Note: lookup in devmap supported since 0cdbb4b09a0.
+ * If not supported will fail with:
+ * cannot pass map_type 14 into func bpf_map_lookup_elem#1:
+ */
+ if (!bpf_map_lookup_elem(&xdp_tx_ports, &fib_params.ifindex))
+ return XDP_PASS;
+
if (h_proto == htons(ETH_P_IP))
ip_decrease_ttl(iph);
else if (h_proto == htons(ETH_P_IPV6))
@@ -117,7 +137,7 @@
memcpy(eth->h_dest, fib_params.dmac, ETH_ALEN);
memcpy(eth->h_source, fib_params.smac, ETH_ALEN);
- return bpf_redirect_map(&tx_port, fib_params.ifindex, 0);
+ return bpf_redirect_map(&xdp_tx_ports, fib_params.ifindex, 0);
}
return XDP_PASS;
--
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