Loading...
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 | #include <stddef.h> #include <inttypes.h> #include <errno.h> #include <linux/seg6_local.h> #include <linux/bpf.h> #include <bpf/bpf_helpers.h> #include <bpf/bpf_endian.h> /* Packet parsing state machine helpers. */ #define cursor_advance(_cursor, _len) \ ({ void *_tmp = _cursor; _cursor += _len; _tmp; }) #define SR6_FLAG_ALERT (1 << 4) #define BPF_PACKET_HEADER __attribute__((packed)) struct ip6_t { unsigned int ver:4; unsigned int priority:8; unsigned int flow_label:20; unsigned short payload_len; unsigned char next_header; unsigned char hop_limit; unsigned long long src_hi; unsigned long long src_lo; unsigned long long dst_hi; unsigned long long dst_lo; } BPF_PACKET_HEADER; struct ip6_addr_t { unsigned long long hi; unsigned long long lo; } BPF_PACKET_HEADER; struct ip6_srh_t { unsigned char nexthdr; unsigned char hdrlen; unsigned char type; unsigned char segments_left; unsigned char first_segment; unsigned char flags; unsigned short tag; struct ip6_addr_t segments[0]; } BPF_PACKET_HEADER; struct sr6_tlv_t { unsigned char type; unsigned char len; unsigned char value[0]; } BPF_PACKET_HEADER; static __always_inline struct ip6_srh_t *get_srh(struct __sk_buff *skb) { void *cursor, *data_end; struct ip6_srh_t *srh; struct ip6_t *ip; uint8_t *ipver; data_end = (void *)(long)skb->data_end; cursor = (void *)(long)skb->data; ipver = (uint8_t *)cursor; if ((void *)ipver + sizeof(*ipver) > data_end) return NULL; if ((*ipver >> 4) != 6) return NULL; ip = cursor_advance(cursor, sizeof(*ip)); if ((void *)ip + sizeof(*ip) > data_end) return NULL; if (ip->next_header != 43) return NULL; srh = cursor_advance(cursor, sizeof(*srh)); if ((void *)srh + sizeof(*srh) > data_end) return NULL; if (srh->type != 4) return NULL; return srh; } static __always_inline int update_tlv_pad(struct __sk_buff *skb, uint32_t new_pad, uint32_t old_pad, uint32_t pad_off) { int err; if (new_pad != old_pad) { err = bpf_lwt_seg6_adjust_srh(skb, pad_off, (int) new_pad - (int) old_pad); if (err) return err; } if (new_pad > 0) { char pad_tlv_buf[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}; struct sr6_tlv_t *pad_tlv = (struct sr6_tlv_t *) pad_tlv_buf; pad_tlv->type = SR6_TLV_PADDING; pad_tlv->len = new_pad - 2; err = bpf_lwt_seg6_store_bytes(skb, pad_off, (void *)pad_tlv_buf, new_pad); if (err) return err; } return 0; } static __always_inline int is_valid_tlv_boundary(struct __sk_buff *skb, struct ip6_srh_t *srh, uint32_t *tlv_off, uint32_t *pad_size, uint32_t *pad_off) { uint32_t srh_off, cur_off; int offset_valid = 0; int err; srh_off = (char *)srh - (char *)(long)skb->data; // cur_off = end of segments, start of possible TLVs cur_off = srh_off + sizeof(*srh) + sizeof(struct ip6_addr_t) * (srh->first_segment + 1); *pad_off = 0; // we can only go as far as ~10 TLVs due to the BPF max stack size #pragma clang loop unroll(full) for (int i = 0; i < 10; i++) { struct sr6_tlv_t tlv; if (cur_off == *tlv_off) offset_valid = 1; if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3)) break; err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv)); if (err) return err; if (tlv.type == SR6_TLV_PADDING) { *pad_size = tlv.len + sizeof(tlv); *pad_off = cur_off; if (*tlv_off == srh_off) { *tlv_off = cur_off; offset_valid = 1; } break; } else if (tlv.type == SR6_TLV_HMAC) { break; } cur_off += sizeof(tlv) + tlv.len; } // we reached the padding or HMAC TLVs, or the end of the SRH if (*pad_off == 0) *pad_off = cur_off; if (*tlv_off == -1) *tlv_off = cur_off; else if (!offset_valid) return -EINVAL; return 0; } static __always_inline int add_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh, uint32_t tlv_off, struct sr6_tlv_t *itlv, uint8_t tlv_size) { uint32_t srh_off = (char *)srh - (char *)(long)skb->data; uint8_t len_remaining, new_pad; uint32_t pad_off = 0; uint32_t pad_size = 0; uint32_t partial_srh_len; int err; if (tlv_off != -1) tlv_off += srh_off; if (itlv->type == SR6_TLV_PADDING || itlv->type == SR6_TLV_HMAC) return -EINVAL; err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off); if (err) return err; err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len); if (err) return err; err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size); if (err) return err; // the following can't be moved inside update_tlv_pad because the // bpf verifier has some issues with it pad_off += sizeof(*itlv) + itlv->len; partial_srh_len = pad_off - srh_off; len_remaining = partial_srh_len % 8; new_pad = 8 - len_remaining; if (new_pad == 1) // cannot pad for 1 byte only new_pad = 9; else if (new_pad == 8) new_pad = 0; return update_tlv_pad(skb, new_pad, pad_size, pad_off); } static __always_inline int delete_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh, uint32_t tlv_off) { uint32_t srh_off = (char *)srh - (char *)(long)skb->data; uint8_t len_remaining, new_pad; uint32_t partial_srh_len; uint32_t pad_off = 0; uint32_t pad_size = 0; struct sr6_tlv_t tlv; int err; tlv_off += srh_off; err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off); if (err) return err; err = bpf_skb_load_bytes(skb, tlv_off, &tlv, sizeof(tlv)); if (err) return err; err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, -(sizeof(tlv) + tlv.len)); if (err) return err; pad_off -= sizeof(tlv) + tlv.len; partial_srh_len = pad_off - srh_off; len_remaining = partial_srh_len % 8; new_pad = 8 - len_remaining; if (new_pad == 1) // cannot pad for 1 byte only new_pad = 9; else if (new_pad == 8) new_pad = 0; return update_tlv_pad(skb, new_pad, pad_size, pad_off); } static __always_inline int has_egr_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh) { int tlv_offset = sizeof(struct ip6_t) + sizeof(struct ip6_srh_t) + ((srh->first_segment + 1) << 4); struct sr6_tlv_t tlv; if (bpf_skb_load_bytes(skb, tlv_offset, &tlv, sizeof(struct sr6_tlv_t))) return 0; if (tlv.type == SR6_TLV_EGRESS && tlv.len == 18) { struct ip6_addr_t egr_addr; if (bpf_skb_load_bytes(skb, tlv_offset + 4, &egr_addr, 16)) return 0; // check if egress TLV value is correct if (bpf_be64_to_cpu(egr_addr.hi) == 0xfd00000000000000 && bpf_be64_to_cpu(egr_addr.lo) == 0x4) return 1; } return 0; } // This function will push a SRH with segments fd00::1, fd00::2, fd00::3, // fd00::4 SEC("encap_srh") int __encap_srh(struct __sk_buff *skb) { unsigned long long hi = 0xfd00000000000000; struct ip6_addr_t *seg; struct ip6_srh_t *srh; char srh_buf[72]; // room for 4 segments int err; srh = (struct ip6_srh_t *)srh_buf; srh->nexthdr = 0; srh->hdrlen = 8; srh->type = 4; srh->segments_left = 3; srh->first_segment = 3; srh->flags = 0; srh->tag = 0; seg = (struct ip6_addr_t *)((char *)srh + sizeof(*srh)); #pragma clang loop unroll(full) for (unsigned long long lo = 0; lo < 4; lo++) { seg->lo = bpf_cpu_to_be64(4 - lo); seg->hi = bpf_cpu_to_be64(hi); seg = (struct ip6_addr_t *)((char *)seg + sizeof(*seg)); } err = bpf_lwt_push_encap(skb, 0, (void *)srh, sizeof(srh_buf)); if (err) return BPF_DROP; return BPF_REDIRECT; } // Add an Egress TLV fc00::4, add the flag A, // and apply End.X action to fc42::1 SEC("add_egr_x") int __add_egr_x(struct __sk_buff *skb) { unsigned long long hi = 0xfc42000000000000; unsigned long long lo = 0x1; struct ip6_srh_t *srh = get_srh(skb); uint8_t new_flags = SR6_FLAG_ALERT; struct ip6_addr_t addr; int err, offset; if (srh == NULL) return BPF_DROP; uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4}; err = add_tlv(skb, srh, (srh->hdrlen+1) << 3, (struct sr6_tlv_t *)&tlv, 20); if (err) return BPF_DROP; offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags); err = bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_flags, sizeof(new_flags)); if (err) return BPF_DROP; addr.lo = bpf_cpu_to_be64(lo); addr.hi = bpf_cpu_to_be64(hi); err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X, (void *)&addr, sizeof(addr)); if (err) return BPF_DROP; return BPF_REDIRECT; } // Pop the Egress TLV, reset the flags, change the tag 2442 and finally do a // simple End action SEC("pop_egr") int __pop_egr(struct __sk_buff *skb) { struct ip6_srh_t *srh = get_srh(skb); uint16_t new_tag = bpf_htons(2442); uint8_t new_flags = 0; int err, offset; if (srh == NULL) return BPF_DROP; if (srh->flags != SR6_FLAG_ALERT) return BPF_DROP; if (srh->hdrlen != 11) // 4 segments + Egress TLV + Padding TLV return BPF_DROP; if (!has_egr_tlv(skb, srh)) return BPF_DROP; err = delete_tlv(skb, srh, 8 + (srh->first_segment + 1) * 16); if (err) return BPF_DROP; offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags); if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_flags, sizeof(new_flags))) return BPF_DROP; offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, tag); if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_tag, sizeof(new_tag))) return BPF_DROP; return BPF_OK; } // Inspect if the Egress TLV and flag have been removed, if the tag is correct, // then apply a End.T action to reach the last segment SEC("inspect_t") int __inspect_t(struct __sk_buff *skb) { struct ip6_srh_t *srh = get_srh(skb); int table = 117; int err; if (srh == NULL) return BPF_DROP; if (srh->flags != 0) return BPF_DROP; if (srh->tag != bpf_htons(2442)) return BPF_DROP; if (srh->hdrlen != 8) // 4 segments return BPF_DROP; err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_T, (void *)&table, sizeof(table)); if (err) return BPF_DROP; return BPF_REDIRECT; } char __license[] SEC("license") = "GPL"; |