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Diffstat (limited to '')
| -rw-r--r-- | samples/bpf/xdp_adjust_tail_kern.c | 155 |
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"; |