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-rw-r--r--samples/bpf/xdp_adjust_tail_kern.c155
1 files changed, 155 insertions, 0 deletions
diff --git a/samples/bpf/xdp_adjust_tail_kern.c b/samples/bpf/xdp_adjust_tail_kern.c
new file mode 100644
index 000000000..ffdd54862
--- /dev/null
+++ b/samples/bpf/xdp_adjust_tail_kern.c
@@ -0,0 +1,155 @@
+/* SPDX-License-Identifier: GPL-2.0
+ * Copyright (c) 2018 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * This program shows how to use bpf_xdp_adjust_tail() by
+ * generating ICMPv4 "packet to big" (unreachable/ df bit set frag needed
+ * to be more preice in case of v4)" where receiving packets bigger then
+ * 600 bytes.
+ */
+#define KBUILD_MODNAME "foo"
+#include <uapi/linux/bpf.h>
+#include <linux/in.h>
+#include <linux/if_ether.h>
+#include <linux/if_packet.h>
+#include <linux/if_vlan.h>
+#include <linux/ip.h>
+#include <linux/icmp.h>
+#include <bpf/bpf_helpers.h>
+
+#define DEFAULT_TTL 64
+#define MAX_PCKT_SIZE 600
+#define ICMP_TOOBIG_SIZE 98
+#define ICMP_TOOBIG_PAYLOAD_SIZE 92
+
+/* volatile to prevent compiler optimizations */
+static volatile __u32 max_pcktsz = MAX_PCKT_SIZE;
+
+struct {
+ __uint(type, BPF_MAP_TYPE_ARRAY);
+ __type(key, __u32);
+ __type(value, __u64);
+ __uint(max_entries, 1);
+} icmpcnt SEC(".maps");
+
+static __always_inline void count_icmp(void)
+{
+ u64 key = 0;
+ u64 *icmp_count;
+
+ icmp_count = bpf_map_lookup_elem(&icmpcnt, &key);
+ if (icmp_count)
+ *icmp_count += 1;
+}
+
+static __always_inline void swap_mac(void *data, struct ethhdr *orig_eth)
+{
+ struct ethhdr *eth;
+
+ eth = data;
+ memcpy(eth->h_source, orig_eth->h_dest, ETH_ALEN);
+ memcpy(eth->h_dest, orig_eth->h_source, ETH_ALEN);
+ eth->h_proto = orig_eth->h_proto;
+}
+
+static __always_inline __u16 csum_fold_helper(__u32 csum)
+{
+ return ~((csum & 0xffff) + (csum >> 16));
+}
+
+static __always_inline void ipv4_csum(void *data_start, int data_size,
+ __u32 *csum)
+{
+ *csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
+ *csum = csum_fold_helper(*csum);
+}
+
+static __always_inline int send_icmp4_too_big(struct xdp_md *xdp)
+{
+ int headroom = (int)sizeof(struct iphdr) + (int)sizeof(struct icmphdr);
+
+ if (bpf_xdp_adjust_head(xdp, 0 - headroom))
+ return XDP_DROP;
+ void *data = (void *)(long)xdp->data;
+ void *data_end = (void *)(long)xdp->data_end;
+
+ if (data + (ICMP_TOOBIG_SIZE + headroom) > data_end)
+ return XDP_DROP;
+
+ struct iphdr *iph, *orig_iph;
+ struct icmphdr *icmp_hdr;
+ struct ethhdr *orig_eth;
+ __u32 csum = 0;
+ __u64 off = 0;
+
+ orig_eth = data + headroom;
+ swap_mac(data, orig_eth);
+ off += sizeof(struct ethhdr);
+ iph = data + off;
+ off += sizeof(struct iphdr);
+ icmp_hdr = data + off;
+ off += sizeof(struct icmphdr);
+ orig_iph = data + off;
+ icmp_hdr->type = ICMP_DEST_UNREACH;
+ icmp_hdr->code = ICMP_FRAG_NEEDED;
+ icmp_hdr->un.frag.mtu = htons(max_pcktsz - sizeof(struct ethhdr));
+ icmp_hdr->checksum = 0;
+ ipv4_csum(icmp_hdr, ICMP_TOOBIG_PAYLOAD_SIZE, &csum);
+ icmp_hdr->checksum = csum;
+ iph->ttl = DEFAULT_TTL;
+ iph->daddr = orig_iph->saddr;
+ iph->saddr = orig_iph->daddr;
+ iph->version = 4;
+ iph->ihl = 5;
+ iph->protocol = IPPROTO_ICMP;
+ iph->tos = 0;
+ iph->tot_len = htons(
+ ICMP_TOOBIG_SIZE + headroom - sizeof(struct ethhdr));
+ iph->check = 0;
+ csum = 0;
+ ipv4_csum(iph, sizeof(struct iphdr), &csum);
+ iph->check = csum;
+ count_icmp();
+ return XDP_TX;
+}
+
+
+static __always_inline int handle_ipv4(struct xdp_md *xdp)
+{
+ void *data_end = (void *)(long)xdp->data_end;
+ void *data = (void *)(long)xdp->data;
+ int pckt_size = data_end - data;
+ int offset;
+
+ if (pckt_size > max(max_pcktsz, ICMP_TOOBIG_SIZE)) {
+ offset = pckt_size - ICMP_TOOBIG_SIZE;
+ if (bpf_xdp_adjust_tail(xdp, 0 - offset))
+ return XDP_PASS;
+ return send_icmp4_too_big(xdp);
+ }
+ return XDP_PASS;
+}
+
+SEC("xdp_icmp")
+int _xdp_icmp(struct xdp_md *xdp)
+{
+ void *data_end = (void *)(long)xdp->data_end;
+ void *data = (void *)(long)xdp->data;
+ struct ethhdr *eth = data;
+ __u16 h_proto;
+
+ if (eth + 1 > data_end)
+ return XDP_DROP;
+
+ h_proto = eth->h_proto;
+
+ if (h_proto == htons(ETH_P_IP))
+ return handle_ipv4(xdp);
+ else
+ return XDP_PASS;
+}
+
+char _license[] SEC("license") = "GPL";