429 lines · c
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 19struct 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 32struct ip6_addr_t {33 unsigned long long hi;34 unsigned long long lo;35} BPF_PACKET_HEADER;36 37struct 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 49struct sr6_tlv_t {50 unsigned char type;51 unsigned char len;52 unsigned char value[0];53} BPF_PACKET_HEADER;54 55static __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 89static __always_inline90int 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 119static __always_inline120int 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 TLVs130 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 size136 __pragma_loop_unroll_full137 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 SRH166 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 178static __always_inline179int 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 the208 // bpf verifier has some issues with it209 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 only215 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 222static __always_inline223int 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 only253 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 260static __always_inline261int 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 correct277 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::4287SEC("encap_srh")288int __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 segments294 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_full308 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::1323SEC("add_egr_x")324int __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 a360// simple End action361SEC("pop_egr")362int __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 TLV376 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 segment400SEC("inspect_t")401int __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 segments417 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 428char __license[] SEC("license") = "GPL";429