root/tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c

DEFINITIONS

1. gen_syncookie
2. check_syncookie
3. SEC
4. SEC

   1 // SPDX-License-Identifier: GPL-2.0
   2 // Copyright (c) 2018 Facebook
   3 // Copyright (c) 2019 Cloudflare
   4 
   5 #include <string.h>
   6 
   7 #include <linux/bpf.h>
   8 #include <linux/pkt_cls.h>
   9 #include <linux/if_ether.h>
  10 #include <linux/in.h>
  11 #include <linux/ip.h>
  12 #include <linux/ipv6.h>
  13 #include <sys/socket.h>
  14 #include <linux/tcp.h>
  15 
  16 #include "bpf_helpers.h"
  17 #include "bpf_endian.h"
  18 
  19 struct bpf_map_def SEC("maps") results = {
  20         .type = BPF_MAP_TYPE_ARRAY,
  21         .key_size = sizeof(__u32),
  22         .value_size = sizeof(__u32),
  23         .max_entries = 3,
  24 };
  25 
  26 static __always_inline __s64 gen_syncookie(void *data_end, struct bpf_sock *sk,
  27                                            void *iph, __u32 ip_size,
  28                                            struct tcphdr *tcph)
  29 {
  30         __u32 thlen = tcph->doff * 4;
  31 
  32         if (tcph->syn && !tcph->ack) {
  33                 // packet should only have an MSS option
  34                 if (thlen != 24)
  35                         return 0;
  36 
  37                 if ((void *)tcph + thlen > data_end)
  38                         return 0;
  39 
  40                 return bpf_tcp_gen_syncookie(sk, iph, ip_size, tcph, thlen);
  41         }
  42         return 0;
  43 }
  44 
  45 static __always_inline void check_syncookie(void *ctx, void *data,
  46                                             void *data_end)
  47 {
  48         struct bpf_sock_tuple tup;
  49         struct bpf_sock *sk;
  50         struct ethhdr *ethh;
  51         struct iphdr *ipv4h;
  52         struct ipv6hdr *ipv6h;
  53         struct tcphdr *tcph;
  54         int ret;
  55         __u32 key_mss = 2;
  56         __u32 key_gen = 1;
  57         __u32 key = 0;
  58         __s64 seq_mss;
  59 
  60         ethh = data;
  61         if (ethh + 1 > data_end)
  62                 return;
  63 
  64         switch (bpf_ntohs(ethh->h_proto)) {
  65         case ETH_P_IP:
  66                 ipv4h = data + sizeof(struct ethhdr);
  67                 if (ipv4h + 1 > data_end)
  68                         return;
  69 
  70                 if (ipv4h->ihl != 5)
  71                         return;
  72 
  73                 tcph = data + sizeof(struct ethhdr) + sizeof(struct iphdr);
  74                 if (tcph + 1 > data_end)
  75                         return;
  76 
  77                 tup.ipv4.saddr = ipv4h->saddr;
  78                 tup.ipv4.daddr = ipv4h->daddr;
  79                 tup.ipv4.sport = tcph->source;
  80                 tup.ipv4.dport = tcph->dest;
  81 
  82                 sk = bpf_skc_lookup_tcp(ctx, &tup, sizeof(tup.ipv4),
  83                                         BPF_F_CURRENT_NETNS, 0);
  84                 if (!sk)
  85                         return;
  86 
  87                 if (sk->state != BPF_TCP_LISTEN)
  88                         goto release;
  89 
  90                 seq_mss = gen_syncookie(data_end, sk, ipv4h, sizeof(*ipv4h),
  91                                         tcph);
  92 
  93                 ret = bpf_tcp_check_syncookie(sk, ipv4h, sizeof(*ipv4h),
  94                                               tcph, sizeof(*tcph));
  95                 break;
  96 
  97         case ETH_P_IPV6:
  98                 ipv6h = data + sizeof(struct ethhdr);
  99                 if (ipv6h + 1 > data_end)
 100                         return;
 101 
 102                 if (ipv6h->nexthdr != IPPROTO_TCP)
 103                         return;
 104 
 105                 tcph = data + sizeof(struct ethhdr) + sizeof(struct ipv6hdr);
 106                 if (tcph + 1 > data_end)
 107                         return;
 108 
 109                 memcpy(tup.ipv6.saddr, &ipv6h->saddr, sizeof(tup.ipv6.saddr));
 110                 memcpy(tup.ipv6.daddr, &ipv6h->daddr, sizeof(tup.ipv6.daddr));
 111                 tup.ipv6.sport = tcph->source;
 112                 tup.ipv6.dport = tcph->dest;
 113 
 114                 sk = bpf_skc_lookup_tcp(ctx, &tup, sizeof(tup.ipv6),
 115                                         BPF_F_CURRENT_NETNS, 0);
 116                 if (!sk)
 117                         return;
 118 
 119                 if (sk->state != BPF_TCP_LISTEN)
 120                         goto release;
 121 
 122                 seq_mss = gen_syncookie(data_end, sk, ipv6h, sizeof(*ipv6h),
 123                                         tcph);
 124 
 125                 ret = bpf_tcp_check_syncookie(sk, ipv6h, sizeof(*ipv6h),
 126                                               tcph, sizeof(*tcph));
 127                 break;
 128 
 129         default:
 130                 return;
 131         }
 132 
 133         if (seq_mss > 0) {
 134                 __u32 cookie = (__u32)seq_mss;
 135                 __u32 mss = seq_mss >> 32;
 136 
 137                 bpf_map_update_elem(&results, &key_gen, &cookie, 0);
 138                 bpf_map_update_elem(&results, &key_mss, &mss, 0);
 139         }
 140 
 141         if (ret == 0) {
 142                 __u32 cookie = bpf_ntohl(tcph->ack_seq) - 1;
 143 
 144                 bpf_map_update_elem(&results, &key, &cookie, 0);
 145         }
 146 
 147 release:
 148         bpf_sk_release(sk);
 149 }
 150 
 151 SEC("clsact/check_syncookie")
 152 int check_syncookie_clsact(struct __sk_buff *skb)
 153 {
 154         check_syncookie(skb, (void *)(long)skb->data,
 155                         (void *)(long)skb->data_end);
 156         return TC_ACT_OK;
 157 }
 158 
 159 SEC("xdp/check_syncookie")
 160 int check_syncookie_xdp(struct xdp_md *ctx)
 161 {
 162         check_syncookie(ctx, (void *)(long)ctx->data,
 163                         (void *)(long)ctx->data_end);
 164         return XDP_PASS;
 165 }
 166 
 167 char _license[] SEC("license") = "GPL";