1 #include <stddef.h> 2 #include <inttypes.h> 3 #include <errno.h> 4 #include <linux/seg6_local.h> 5 #include <linux/bpf.h> 6 #include <bpf/bpf_helpers.h> 7 #include <bpf/bpf_endian.h> 8 9 /* Packet parsing state machine helpers. */ 10 #define cursor_advance(_cursor, _len) \ 11 ({ void *_tmp = _cursor; _cursor += _len; _tmp; }) 12 13 #define SR6_FLAG_ALERT (1 << 4) 14 15 #define BPF_PACKET_HEADER __attribute__((packed)) 16 17 struct ip6_t { 18 unsigned int ver:4; 19 unsigned int priority:8; 20 unsigned int flow_label:20; 21 unsigned short payload_len; 22 unsigned char next_header; 23 unsigned char hop_limit; 24 unsigned long long src_hi; 25 unsigned long long src_lo; 26 unsigned long long dst_hi; 27 unsigned long long dst_lo; 28 } BPF_PACKET_HEADER; 29 30 struct ip6_addr_t { 31 unsigned long long hi; 32 unsigned long long lo; 33 } BPF_PACKET_HEADER; 34 35 struct ip6_srh_t { 36 unsigned char nexthdr; 37 unsigned char hdrlen; 38 unsigned char type; 39 unsigned char segments_left; 40 unsigned char first_segment; 41 unsigned char flags; 42 unsigned short tag; 43 44 struct ip6_addr_t segments[0]; 45 } BPF_PACKET_HEADER; 46 47 struct sr6_tlv_t { 48 unsigned char type; 49 unsigned char len; 50 unsigned char value[0]; 51 } BPF_PACKET_HEADER; 52 53 static __always_inline struct ip6_srh_t *get_srh(struct __sk_buff *skb) 54 { 55 void *cursor, *data_end; 56 struct ip6_srh_t *srh; 57 struct ip6_t *ip; 58 uint8_t *ipver; 59 60 data_end = (void *)(long)skb->data_end; 61 cursor = (void *)(long)skb->data; 62 ipver = (uint8_t *)cursor; 63 64 if ((void *)ipver + sizeof(*ipver) > data_end) 65 return NULL; 66 67 if ((*ipver >> 4) != 6) 68 return NULL; 69 70 ip = cursor_advance(cursor, sizeof(*ip)); 71 if ((void *)ip + sizeof(*ip) > data_end) 72 return NULL; 73 74 if (ip->next_header != 43) 75 return NULL; 76 77 srh = cursor_advance(cursor, sizeof(*srh)); 78 if ((void *)srh + sizeof(*srh) > data_end) 79 return NULL; 80 81 if (srh->type != 4) 82 return NULL; 83 84 return srh; 85 } 86 87 static __always_inline int update_tlv_pad(struct __sk_buff *skb, 88 uint32_t new_pad, uint32_t old_pad, 89 uint32_t pad_off) 90 { 91 int err; 92 93 if (new_pad != old_pad) { 94 err = bpf_lwt_seg6_adjust_srh(skb, pad_off, 95 (int) new_pad - (int) old_pad); 96 if (err) 97 return err; 98 } 99 100 if (new_pad > 0) { 101 char pad_tlv_buf[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 102 0, 0, 0}; 103 struct sr6_tlv_t *pad_tlv = (struct sr6_tlv_t *) pad_tlv_buf; 104 105 pad_tlv->type = SR6_TLV_PADDING; 106 pad_tlv->len = new_pad - 2; 107 108 err = bpf_lwt_seg6_store_bytes(skb, pad_off, 109 (void *)pad_tlv_buf, new_pad); 110 if (err) 111 return err; 112 } 113 114 return 0; 115 } 116 117 static __always_inline int is_valid_tlv_boundary(struct __sk_buff *skb, 118 struct ip6_srh_t *srh, 119 uint32_t *tlv_off, 120 uint32_t *pad_size, 121 uint32_t *pad_off) 122 { 123 uint32_t srh_off, cur_off; 124 int offset_valid = 0; 125 int err; 126 127 srh_off = (char *)srh - (char *)(long)skb->data; 128 // cur_off = end of segments, start of possible TLVs 129 cur_off = srh_off + sizeof(*srh) + 130 sizeof(struct ip6_addr_t) * (srh->first_segment + 1); 131 132 *pad_off = 0; 133 134 // we can only go as far as ~10 TLVs due to the BPF max stack size 135 // workaround: define induction variable "i" as "long" instead 136 // of "int" to prevent alu32 sub-register spilling. 137 #pragma clang loop unroll(disable) 138 for (long i = 0; i < 100; i++) { 139 struct sr6_tlv_t tlv; 140 141 if (cur_off == *tlv_off) 142 offset_valid = 1; 143 144 if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3)) 145 break; 146 147 err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv)); 148 if (err) 149 return err; 150 151 if (tlv.type == SR6_TLV_PADDING) { 152 *pad_size = tlv.len + sizeof(tlv); 153 *pad_off = cur_off; 154 155 if (*tlv_off == srh_off) { 156 *tlv_off = cur_off; 157 offset_valid = 1; 158 } 159 break; 160 161 } else if (tlv.type == SR6_TLV_HMAC) { 162 break; 163 } 164 165 cur_off += sizeof(tlv) + tlv.len; 166 } // we reached the padding or HMAC TLVs, or the end of the SRH 167 168 if (*pad_off == 0) 169 *pad_off = cur_off; 170 171 if (*tlv_off == -1) 172 *tlv_off = cur_off; 173 else if (!offset_valid) 174 return -EINVAL; 175 176 return 0; 177 } 178 179 static __always_inline int add_tlv(struct __sk_buff *skb, 180 struct ip6_srh_t *srh, uint32_t tlv_off, 181 struct sr6_tlv_t *itlv, uint8_t tlv_size) 182 { 183 uint32_t srh_off = (char *)srh - (char *)(long)skb->data; 184 uint8_t len_remaining, new_pad; 185 uint32_t pad_off = 0; 186 uint32_t pad_size = 0; 187 uint32_t partial_srh_len; 188 int err; 189 190 if (tlv_off != -1) 191 tlv_off += srh_off; 192 193 if (itlv->type == SR6_TLV_PADDING || itlv->type == SR6_TLV_HMAC) 194 return -EINVAL; 195 196 err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off); 197 if (err) 198 return err; 199 200 err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len); 201 if (err) 202 return err; 203 204 err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size); 205 if (err) 206 return err; 207 208 // the following can't be moved inside update_tlv_pad because the 209 // bpf verifier has some issues with it 210 pad_off += sizeof(*itlv) + itlv->len; 211 partial_srh_len = pad_off - srh_off; 212 len_remaining = partial_srh_len % 8; 213 new_pad = 8 - len_remaining; 214 215 if (new_pad == 1) // cannot pad for 1 byte only 216 new_pad = 9; 217 else if (new_pad == 8) 218 new_pad = 0; 219 220 return update_tlv_pad(skb, new_pad, pad_size, pad_off); 221 } 222 223 // Add an Egress TLV fc00::4, add the flag A, 224 // and apply End.X action to fc42::1 225 SEC("lwt_seg6local") 226 int __add_egr_x(struct __sk_buff *skb) 227 { 228 unsigned long long hi = 0xfc42000000000000; 229 unsigned long long lo = 0x1; 230 struct ip6_srh_t *srh = get_srh(skb); 231 uint8_t new_flags = SR6_FLAG_ALERT; 232 struct ip6_addr_t addr; 233 int err, offset; 234 235 if (srh == NULL) 236 return BPF_DROP; 237 238 uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 239 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4}; 240 241 err = add_tlv(skb, srh, (srh->hdrlen+1) << 3, 242 (struct sr6_tlv_t *)&tlv, 20); 243 if (err) 244 return BPF_DROP; 245 246 offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags); 247 err = bpf_lwt_seg6_store_bytes(skb, offset, 248 (void *)&new_flags, sizeof(new_flags)); 249 if (err) 250 return BPF_DROP; 251 252 addr.lo = bpf_cpu_to_be64(lo); 253 addr.hi = bpf_cpu_to_be64(hi); 254 err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X, 255 (void *)&addr, sizeof(addr)); 256 if (err) 257 return BPF_DROP; 258 return BPF_REDIRECT; 259 } 260 char __license[] SEC("license") = "GPL"; 261