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 #include "bpf_compiler.h" 10 11 /* Packet parsing state machine helpers. */ 12 #define cursor_advance(_cursor, _len) \ 13 ({ void *_tmp = _cursor; _cursor += _len; _tmp; }) 14 15 #define SR6_FLAG_ALERT (1 << 4) 16 17 #define BPF_PACKET_HEADER __attribute__((packed)) 18 19 struct ip6_t { 20 unsigned int ver:4; 21 unsigned int priority:8; 22 unsigned int flow_label:20; 23 unsigned short payload_len; 24 unsigned char next_header; 25 unsigned char hop_limit; 26 unsigned long long src_hi; 27 unsigned long long src_lo; 28 unsigned long long dst_hi; 29 unsigned long long dst_lo; 30 } BPF_PACKET_HEADER; 31 32 struct ip6_addr_t { 33 unsigned long long hi; 34 unsigned long long lo; 35 } BPF_PACKET_HEADER; 36 37 struct ip6_srh_t { 38 unsigned char nexthdr; 39 unsigned char hdrlen; 40 unsigned char type; 41 unsigned char segments_left; 42 unsigned char first_segment; 43 unsigned char flags; 44 unsigned short tag; 45 46 struct ip6_addr_t segments[0]; 47 } BPF_PACKET_HEADER; 48 49 struct sr6_tlv_t { 50 unsigned char type; 51 unsigned char len; 52 unsigned char value[0]; 53 } BPF_PACKET_HEADER; 54 55 static __always_inline struct ip6_srh_t *get_srh(struct __sk_buff *skb) 56 { 57 void *cursor, *data_end; 58 struct ip6_srh_t *srh; 59 struct ip6_t *ip; 60 uint8_t *ipver; 61 62 data_end = (void *)(long)skb->data_end; 63 cursor = (void *)(long)skb->data; 64 ipver = (uint8_t *)cursor; 65 66 if ((void *)ipver + sizeof(*ipver) > data_end) 67 return NULL; 68 69 if ((*ipver >> 4) != 6) 70 return NULL; 71 72 ip = cursor_advance(cursor, sizeof(*ip)); 73 if ((void *)ip + sizeof(*ip) > data_end) 74 return NULL; 75 76 if (ip->next_header != 43) 77 return NULL; 78 79 srh = cursor_advance(cursor, sizeof(*srh)); 80 if ((void *)srh + sizeof(*srh) > data_end) 81 return NULL; 82 83 if (srh->type != 4) 84 return NULL; 85 86 return srh; 87 } 88 89 static __always_inline 90 int update_tlv_pad(struct __sk_buff *skb, uint32_t new_pad, 91 uint32_t old_pad, uint32_t pad_off) 92 { 93 int err; 94 95 if (new_pad != old_pad) { 96 err = bpf_lwt_seg6_adjust_srh(skb, pad_off, 97 (int) new_pad - (int) old_pad); 98 if (err) 99 return err; 100 } 101 102 if (new_pad > 0) { 103 char pad_tlv_buf[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 104 0, 0, 0}; 105 struct sr6_tlv_t *pad_tlv = (struct sr6_tlv_t *) pad_tlv_buf; 106 107 pad_tlv->type = SR6_TLV_PADDING; 108 pad_tlv->len = new_pad - 2; 109 110 err = bpf_lwt_seg6_store_bytes(skb, pad_off, 111 (void *)pad_tlv_buf, new_pad); 112 if (err) 113 return err; 114 } 115 116 return 0; 117 } 118 119 static __always_inline 120 int is_valid_tlv_boundary(struct __sk_buff *skb, struct ip6_srh_t *srh, 121 uint32_t *tlv_off, uint32_t *pad_size, 122 uint32_t *pad_off) 123 { 124 uint32_t srh_off, cur_off; 125 int offset_valid = 0; 126 int err; 127 128 srh_off = (char *)srh - (char *)(long)skb->data; 129 // cur_off = end of segments, start of possible TLVs 130 cur_off = srh_off + sizeof(*srh) + 131 sizeof(struct ip6_addr_t) * (srh->first_segment + 1); 132 133 *pad_off = 0; 134 135 // we can only go as far as ~10 TLVs due to the BPF max stack size 136 __pragma_loop_unroll_full 137 for (int i = 0; i < 10; i++) { 138 struct sr6_tlv_t tlv; 139 140 if (cur_off == *tlv_off) 141 offset_valid = 1; 142 143 if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3)) 144 break; 145 146 err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv)); 147 if (err) 148 return err; 149 150 if (tlv.type == SR6_TLV_PADDING) { 151 *pad_size = tlv.len + sizeof(tlv); 152 *pad_off = cur_off; 153 154 if (*tlv_off == srh_off) { 155 *tlv_off = cur_off; 156 offset_valid = 1; 157 } 158 break; 159 160 } else if (tlv.type == SR6_TLV_HMAC) { 161 break; 162 } 163 164 cur_off += sizeof(tlv) + tlv.len; 165 } // we reached the padding or HMAC TLVs, or the end of the SRH 166 167 if (*pad_off == 0) 168 *pad_off = cur_off; 169 170 if (*tlv_off == -1) 171 *tlv_off = cur_off; 172 else if (!offset_valid) 173 return -EINVAL; 174 175 return 0; 176 } 177 178 static __always_inline 179 int add_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh, uint32_t tlv_off, 180 struct sr6_tlv_t *itlv, uint8_t tlv_size) 181 { 182 uint32_t srh_off = (char *)srh - (char *)(long)skb->data; 183 uint8_t len_remaining, new_pad; 184 uint32_t pad_off = 0; 185 uint32_t pad_size = 0; 186 uint32_t partial_srh_len; 187 int err; 188 189 if (tlv_off != -1) 190 tlv_off += srh_off; 191 192 if (itlv->type == SR6_TLV_PADDING || itlv->type == SR6_TLV_HMAC) 193 return -EINVAL; 194 195 err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off); 196 if (err) 197 return err; 198 199 err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len); 200 if (err) 201 return err; 202 203 err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size); 204 if (err) 205 return err; 206 207 // the following can't be moved inside update_tlv_pad because the 208 // bpf verifier has some issues with it 209 pad_off += sizeof(*itlv) + itlv->len; 210 partial_srh_len = pad_off - srh_off; 211 len_remaining = partial_srh_len % 8; 212 new_pad = 8 - len_remaining; 213 214 if (new_pad == 1) // cannot pad for 1 byte only 215 new_pad = 9; 216 else if (new_pad == 8) 217 new_pad = 0; 218 219 return update_tlv_pad(skb, new_pad, pad_size, pad_off); 220 } 221 222 static __always_inline 223 int delete_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh, 224 uint32_t tlv_off) 225 { 226 uint32_t srh_off = (char *)srh - (char *)(long)skb->data; 227 uint8_t len_remaining, new_pad; 228 uint32_t partial_srh_len; 229 uint32_t pad_off = 0; 230 uint32_t pad_size = 0; 231 struct sr6_tlv_t tlv; 232 int err; 233 234 tlv_off += srh_off; 235 236 err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off); 237 if (err) 238 return err; 239 240 err = bpf_skb_load_bytes(skb, tlv_off, &tlv, sizeof(tlv)); 241 if (err) 242 return err; 243 244 err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, -(sizeof(tlv) + tlv.len)); 245 if (err) 246 return err; 247 248 pad_off -= sizeof(tlv) + tlv.len; 249 partial_srh_len = pad_off - srh_off; 250 len_remaining = partial_srh_len % 8; 251 new_pad = 8 - len_remaining; 252 if (new_pad == 1) // cannot pad for 1 byte only 253 new_pad = 9; 254 else if (new_pad == 8) 255 new_pad = 0; 256 257 return update_tlv_pad(skb, new_pad, pad_size, pad_off); 258 } 259 260 static __always_inline 261 int has_egr_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh) 262 { 263 int tlv_offset = sizeof(struct ip6_t) + sizeof(struct ip6_srh_t) + 264 ((srh->first_segment + 1) << 4); 265 struct sr6_tlv_t tlv; 266 267 if (bpf_skb_load_bytes(skb, tlv_offset, &tlv, sizeof(struct sr6_tlv_t))) 268 return 0; 269 270 if (tlv.type == SR6_TLV_EGRESS && tlv.len == 18) { 271 struct ip6_addr_t egr_addr; 272 273 if (bpf_skb_load_bytes(skb, tlv_offset + 4, &egr_addr, 16)) 274 return 0; 275 276 // check if egress TLV value is correct 277 if (bpf_be64_to_cpu(egr_addr.hi) == 0xfd00000000000000 && 278 bpf_be64_to_cpu(egr_addr.lo) == 0x4) 279 return 1; 280 } 281 282 return 0; 283 } 284 285 // This function will push a SRH with segments fd00::1, fd00::2, fd00::3, 286 // fd00::4 287 SEC("encap_srh") 288 int __encap_srh(struct __sk_buff *skb) 289 { 290 unsigned long long hi = 0xfd00000000000000; 291 struct ip6_addr_t *seg; 292 struct ip6_srh_t *srh; 293 char srh_buf[72]; // room for 4 segments 294 int err; 295 296 srh = (struct ip6_srh_t *)srh_buf; 297 srh->nexthdr = 0; 298 srh->hdrlen = 8; 299 srh->type = 4; 300 srh->segments_left = 3; 301 srh->first_segment = 3; 302 srh->flags = 0; 303 srh->tag = 0; 304 305 seg = (struct ip6_addr_t *)((char *)srh + sizeof(*srh)); 306 307 __pragma_loop_unroll_full 308 for (unsigned long long lo = 0; lo < 4; lo++) { 309 seg->lo = bpf_cpu_to_be64(4 - lo); 310 seg->hi = bpf_cpu_to_be64(hi); 311 seg = (struct ip6_addr_t *)((char *)seg + sizeof(*seg)); 312 } 313 314 err = bpf_lwt_push_encap(skb, 0, (void *)srh, sizeof(srh_buf)); 315 if (err) 316 return BPF_DROP; 317 318 return BPF_REDIRECT; 319 } 320 321 // Add an Egress TLV fc00::4, add the flag A, 322 // and apply End.X action to fc42::1 323 SEC("add_egr_x") 324 int __add_egr_x(struct __sk_buff *skb) 325 { 326 unsigned long long hi = 0xfc42000000000000; 327 unsigned long long lo = 0x1; 328 struct ip6_srh_t *srh = get_srh(skb); 329 uint8_t new_flags = SR6_FLAG_ALERT; 330 struct ip6_addr_t addr; 331 int err, offset; 332 333 if (srh == NULL) 334 return BPF_DROP; 335 336 uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 337 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4}; 338 339 err = add_tlv(skb, srh, (srh->hdrlen+1) << 3, 340 (struct sr6_tlv_t *)&tlv, 20); 341 if (err) 342 return BPF_DROP; 343 344 offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags); 345 err = bpf_lwt_seg6_store_bytes(skb, offset, 346 (void *)&new_flags, sizeof(new_flags)); 347 if (err) 348 return BPF_DROP; 349 350 addr.lo = bpf_cpu_to_be64(lo); 351 addr.hi = bpf_cpu_to_be64(hi); 352 err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X, 353 (void *)&addr, sizeof(addr)); 354 if (err) 355 return BPF_DROP; 356 return BPF_REDIRECT; 357 } 358 359 // Pop the Egress TLV, reset the flags, change the tag 2442 and finally do a 360 // simple End action 361 SEC("pop_egr") 362 int __pop_egr(struct __sk_buff *skb) 363 { 364 struct ip6_srh_t *srh = get_srh(skb); 365 uint16_t new_tag = bpf_htons(2442); 366 uint8_t new_flags = 0; 367 int err, offset; 368 369 if (srh == NULL) 370 return BPF_DROP; 371 372 if (srh->flags != SR6_FLAG_ALERT) 373 return BPF_DROP; 374 375 if (srh->hdrlen != 11) // 4 segments + Egress TLV + Padding TLV 376 return BPF_DROP; 377 378 if (!has_egr_tlv(skb, srh)) 379 return BPF_DROP; 380 381 err = delete_tlv(skb, srh, 8 + (srh->first_segment + 1) * 16); 382 if (err) 383 return BPF_DROP; 384 385 offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags); 386 if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_flags, 387 sizeof(new_flags))) 388 return BPF_DROP; 389 390 offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, tag); 391 if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_tag, 392 sizeof(new_tag))) 393 return BPF_DROP; 394 395 return BPF_OK; 396 } 397 398 // Inspect if the Egress TLV and flag have been removed, if the tag is correct, 399 // then apply a End.T action to reach the last segment 400 SEC("inspect_t") 401 int __inspect_t(struct __sk_buff *skb) 402 { 403 struct ip6_srh_t *srh = get_srh(skb); 404 int table = 117; 405 int err; 406 407 if (srh == NULL) 408 return BPF_DROP; 409 410 if (srh->flags != 0) 411 return BPF_DROP; 412 413 if (srh->tag != bpf_htons(2442)) 414 return BPF_DROP; 415 416 if (srh->hdrlen != 8) // 4 segments 417 return BPF_DROP; 418 419 err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_T, 420 (void *)&table, sizeof(table)); 421 422 if (err) 423 return BPF_DROP; 424 425 return BPF_REDIRECT; 426 } 427 428 char __license[] SEC("license") = "GPL"; 429