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_helpers.h"
7 #include "bpf_endian.h"
8
9 #define bpf_printk(fmt, ...) \
10 ({ \
11 char ____fmt[] = fmt; \
12 bpf_trace_printk(____fmt, sizeof(____fmt), \
13 ##__VA_ARGS__); \
14 })
15
16 /* Packet parsing state machine helpers. */
17 #define cursor_advance(_cursor, _len) \
18 ({ void *_tmp = _cursor; _cursor += _len; _tmp; })
19
20 #define SR6_FLAG_ALERT (1 << 4)
21
22 #define htonll(x) ((bpf_htonl(1)) == 1 ? (x) : ((uint64_t)bpf_htonl((x) & \
23 0xFFFFFFFF) << 32) | bpf_htonl((x) >> 32))
24 #define ntohll(x) ((bpf_ntohl(1)) == 1 ? (x) : ((uint64_t)bpf_ntohl((x) & \
25 0xFFFFFFFF) << 32) | bpf_ntohl((x) >> 32))
26 #define BPF_PACKET_HEADER __attribute__((packed))
27
28 struct ip6_t {
29 unsigned int ver:4;
30 unsigned int priority:8;
31 unsigned int flow_label:20;
32 unsigned short payload_len;
33 unsigned char next_header;
34 unsigned char hop_limit;
35 unsigned long long src_hi;
36 unsigned long long src_lo;
37 unsigned long long dst_hi;
38 unsigned long long dst_lo;
39 } BPF_PACKET_HEADER;
40
41 struct ip6_addr_t {
42 unsigned long long hi;
43 unsigned long long lo;
44 } BPF_PACKET_HEADER;
45
46 struct ip6_srh_t {
47 unsigned char nexthdr;
48 unsigned char hdrlen;
49 unsigned char type;
50 unsigned char segments_left;
51 unsigned char first_segment;
52 unsigned char flags;
53 unsigned short tag;
54
55 struct ip6_addr_t segments[0];
56 } BPF_PACKET_HEADER;
57
58 struct sr6_tlv_t {
59 unsigned char type;
60 unsigned char len;
61 unsigned char value[0];
62 } BPF_PACKET_HEADER;
63
get_srh(struct __sk_buff * skb)64 __attribute__((always_inline)) struct ip6_srh_t *get_srh(struct __sk_buff *skb)
65 {
66 void *cursor, *data_end;
67 struct ip6_srh_t *srh;
68 struct ip6_t *ip;
69 uint8_t *ipver;
70
71 data_end = (void *)(long)skb->data_end;
72 cursor = (void *)(long)skb->data;
73 ipver = (uint8_t *)cursor;
74
75 if ((void *)ipver + sizeof(*ipver) > data_end)
76 return NULL;
77
78 if ((*ipver >> 4) != 6)
79 return NULL;
80
81 ip = cursor_advance(cursor, sizeof(*ip));
82 if ((void *)ip + sizeof(*ip) > data_end)
83 return NULL;
84
85 if (ip->next_header != 43)
86 return NULL;
87
88 srh = cursor_advance(cursor, sizeof(*srh));
89 if ((void *)srh + sizeof(*srh) > data_end)
90 return NULL;
91
92 if (srh->type != 4)
93 return NULL;
94
95 return srh;
96 }
97
98 __attribute__((always_inline))
update_tlv_pad(struct __sk_buff * skb,uint32_t new_pad,uint32_t old_pad,uint32_t pad_off)99 int update_tlv_pad(struct __sk_buff *skb, uint32_t new_pad,
100 uint32_t old_pad, uint32_t pad_off)
101 {
102 int err;
103
104 if (new_pad != old_pad) {
105 err = bpf_lwt_seg6_adjust_srh(skb, pad_off,
106 (int) new_pad - (int) old_pad);
107 if (err)
108 return err;
109 }
110
111 if (new_pad > 0) {
112 char pad_tlv_buf[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
113 0, 0, 0};
114 struct sr6_tlv_t *pad_tlv = (struct sr6_tlv_t *) pad_tlv_buf;
115
116 pad_tlv->type = SR6_TLV_PADDING;
117 pad_tlv->len = new_pad - 2;
118
119 err = bpf_lwt_seg6_store_bytes(skb, pad_off,
120 (void *)pad_tlv_buf, new_pad);
121 if (err)
122 return err;
123 }
124
125 return 0;
126 }
127
128 __attribute__((always_inline))
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)129 int is_valid_tlv_boundary(struct __sk_buff *skb, struct ip6_srh_t *srh,
130 uint32_t *tlv_off, uint32_t *pad_size,
131 uint32_t *pad_off)
132 {
133 uint32_t srh_off, cur_off;
134 int offset_valid = 0;
135 int err;
136
137 srh_off = (char *)srh - (char *)(long)skb->data;
138 // cur_off = end of segments, start of possible TLVs
139 cur_off = srh_off + sizeof(*srh) +
140 sizeof(struct ip6_addr_t) * (srh->first_segment + 1);
141
142 *pad_off = 0;
143
144 // we can only go as far as ~10 TLVs due to the BPF max stack size
145 #pragma clang loop unroll(full)
146 for (int i = 0; i < 10; i++) {
147 struct sr6_tlv_t tlv;
148
149 if (cur_off == *tlv_off)
150 offset_valid = 1;
151
152 if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3))
153 break;
154
155 err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv));
156 if (err)
157 return err;
158
159 if (tlv.type == SR6_TLV_PADDING) {
160 *pad_size = tlv.len + sizeof(tlv);
161 *pad_off = cur_off;
162
163 if (*tlv_off == srh_off) {
164 *tlv_off = cur_off;
165 offset_valid = 1;
166 }
167 break;
168
169 } else if (tlv.type == SR6_TLV_HMAC) {
170 break;
171 }
172
173 cur_off += sizeof(tlv) + tlv.len;
174 } // we reached the padding or HMAC TLVs, or the end of the SRH
175
176 if (*pad_off == 0)
177 *pad_off = cur_off;
178
179 if (*tlv_off == -1)
180 *tlv_off = cur_off;
181 else if (!offset_valid)
182 return -EINVAL;
183
184 return 0;
185 }
186
187 __attribute__((always_inline))
add_tlv(struct __sk_buff * skb,struct ip6_srh_t * srh,uint32_t tlv_off,struct sr6_tlv_t * itlv,uint8_t tlv_size)188 int add_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh, uint32_t tlv_off,
189 struct sr6_tlv_t *itlv, uint8_t tlv_size)
190 {
191 uint32_t srh_off = (char *)srh - (char *)(long)skb->data;
192 uint8_t len_remaining, new_pad;
193 uint32_t pad_off = 0;
194 uint32_t pad_size = 0;
195 uint32_t partial_srh_len;
196 int err;
197
198 if (tlv_off != -1)
199 tlv_off += srh_off;
200
201 if (itlv->type == SR6_TLV_PADDING || itlv->type == SR6_TLV_HMAC)
202 return -EINVAL;
203
204 err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
205 if (err)
206 return err;
207
208 err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len);
209 if (err)
210 return err;
211
212 err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size);
213 if (err)
214 return err;
215
216 // the following can't be moved inside update_tlv_pad because the
217 // bpf verifier has some issues with it
218 pad_off += sizeof(*itlv) + itlv->len;
219 partial_srh_len = pad_off - srh_off;
220 len_remaining = partial_srh_len % 8;
221 new_pad = 8 - len_remaining;
222
223 if (new_pad == 1) // cannot pad for 1 byte only
224 new_pad = 9;
225 else if (new_pad == 8)
226 new_pad = 0;
227
228 return update_tlv_pad(skb, new_pad, pad_size, pad_off);
229 }
230
231 __attribute__((always_inline))
delete_tlv(struct __sk_buff * skb,struct ip6_srh_t * srh,uint32_t tlv_off)232 int delete_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh,
233 uint32_t tlv_off)
234 {
235 uint32_t srh_off = (char *)srh - (char *)(long)skb->data;
236 uint8_t len_remaining, new_pad;
237 uint32_t partial_srh_len;
238 uint32_t pad_off = 0;
239 uint32_t pad_size = 0;
240 struct sr6_tlv_t tlv;
241 int err;
242
243 tlv_off += srh_off;
244
245 err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
246 if (err)
247 return err;
248
249 err = bpf_skb_load_bytes(skb, tlv_off, &tlv, sizeof(tlv));
250 if (err)
251 return err;
252
253 err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, -(sizeof(tlv) + tlv.len));
254 if (err)
255 return err;
256
257 pad_off -= sizeof(tlv) + tlv.len;
258 partial_srh_len = pad_off - srh_off;
259 len_remaining = partial_srh_len % 8;
260 new_pad = 8 - len_remaining;
261 if (new_pad == 1) // cannot pad for 1 byte only
262 new_pad = 9;
263 else if (new_pad == 8)
264 new_pad = 0;
265
266 return update_tlv_pad(skb, new_pad, pad_size, pad_off);
267 }
268
269 __attribute__((always_inline))
has_egr_tlv(struct __sk_buff * skb,struct ip6_srh_t * srh)270 int has_egr_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh)
271 {
272 int tlv_offset = sizeof(struct ip6_t) + sizeof(struct ip6_srh_t) +
273 ((srh->first_segment + 1) << 4);
274 struct sr6_tlv_t tlv;
275
276 if (bpf_skb_load_bytes(skb, tlv_offset, &tlv, sizeof(struct sr6_tlv_t)))
277 return 0;
278
279 if (tlv.type == SR6_TLV_EGRESS && tlv.len == 18) {
280 struct ip6_addr_t egr_addr;
281
282 if (bpf_skb_load_bytes(skb, tlv_offset + 4, &egr_addr, 16))
283 return 0;
284
285 // check if egress TLV value is correct
286 if (ntohll(egr_addr.hi) == 0xfd00000000000000 &&
287 ntohll(egr_addr.lo) == 0x4)
288 return 1;
289 }
290
291 return 0;
292 }
293
294 // This function will push a SRH with segments fd00::1, fd00::2, fd00::3,
295 // fd00::4
296 SEC("encap_srh")
__encap_srh(struct __sk_buff * skb)297 int __encap_srh(struct __sk_buff *skb)
298 {
299 unsigned long long hi = 0xfd00000000000000;
300 struct ip6_addr_t *seg;
301 struct ip6_srh_t *srh;
302 char srh_buf[72]; // room for 4 segments
303 int err;
304
305 srh = (struct ip6_srh_t *)srh_buf;
306 srh->nexthdr = 0;
307 srh->hdrlen = 8;
308 srh->type = 4;
309 srh->segments_left = 3;
310 srh->first_segment = 3;
311 srh->flags = 0;
312 srh->tag = 0;
313
314 seg = (struct ip6_addr_t *)((char *)srh + sizeof(*srh));
315
316 #pragma clang loop unroll(full)
317 for (unsigned long long lo = 0; lo < 4; lo++) {
318 seg->lo = htonll(4 - lo);
319 seg->hi = htonll(hi);
320 seg = (struct ip6_addr_t *)((char *)seg + sizeof(*seg));
321 }
322
323 err = bpf_lwt_push_encap(skb, 0, (void *)srh, sizeof(srh_buf));
324 if (err)
325 return BPF_DROP;
326
327 return BPF_REDIRECT;
328 }
329
330 // Add an Egress TLV fc00::4, add the flag A,
331 // and apply End.X action to fc42::1
332 SEC("add_egr_x")
__add_egr_x(struct __sk_buff * skb)333 int __add_egr_x(struct __sk_buff *skb)
334 {
335 unsigned long long hi = 0xfc42000000000000;
336 unsigned long long lo = 0x1;
337 struct ip6_srh_t *srh = get_srh(skb);
338 uint8_t new_flags = SR6_FLAG_ALERT;
339 struct ip6_addr_t addr;
340 int err, offset;
341
342 if (srh == NULL)
343 return BPF_DROP;
344
345 uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
346 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4};
347
348 err = add_tlv(skb, srh, (srh->hdrlen+1) << 3,
349 (struct sr6_tlv_t *)&tlv, 20);
350 if (err)
351 return BPF_DROP;
352
353 offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
354 err = bpf_lwt_seg6_store_bytes(skb, offset,
355 (void *)&new_flags, sizeof(new_flags));
356 if (err)
357 return BPF_DROP;
358
359 addr.lo = htonll(lo);
360 addr.hi = htonll(hi);
361 err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X,
362 (void *)&addr, sizeof(addr));
363 if (err)
364 return BPF_DROP;
365 return BPF_REDIRECT;
366 }
367
368 // Pop the Egress TLV, reset the flags, change the tag 2442 and finally do a
369 // simple End action
370 SEC("pop_egr")
__pop_egr(struct __sk_buff * skb)371 int __pop_egr(struct __sk_buff *skb)
372 {
373 struct ip6_srh_t *srh = get_srh(skb);
374 uint16_t new_tag = bpf_htons(2442);
375 uint8_t new_flags = 0;
376 int err, offset;
377
378 if (srh == NULL)
379 return BPF_DROP;
380
381 if (srh->flags != SR6_FLAG_ALERT)
382 return BPF_DROP;
383
384 if (srh->hdrlen != 11) // 4 segments + Egress TLV + Padding TLV
385 return BPF_DROP;
386
387 if (!has_egr_tlv(skb, srh))
388 return BPF_DROP;
389
390 err = delete_tlv(skb, srh, 8 + (srh->first_segment + 1) * 16);
391 if (err)
392 return BPF_DROP;
393
394 offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
395 if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_flags,
396 sizeof(new_flags)))
397 return BPF_DROP;
398
399 offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, tag);
400 if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_tag,
401 sizeof(new_tag)))
402 return BPF_DROP;
403
404 return BPF_OK;
405 }
406
407 // Inspect if the Egress TLV and flag have been removed, if the tag is correct,
408 // then apply a End.T action to reach the last segment
409 SEC("inspect_t")
__inspect_t(struct __sk_buff * skb)410 int __inspect_t(struct __sk_buff *skb)
411 {
412 struct ip6_srh_t *srh = get_srh(skb);
413 int table = 117;
414 int err;
415
416 if (srh == NULL)
417 return BPF_DROP;
418
419 if (srh->flags != 0)
420 return BPF_DROP;
421
422 if (srh->tag != bpf_htons(2442))
423 return BPF_DROP;
424
425 if (srh->hdrlen != 8) // 4 segments
426 return BPF_DROP;
427
428 err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_T,
429 (void *)&table, sizeof(table));
430
431 if (err)
432 return BPF_DROP;
433
434 return BPF_REDIRECT;
435 }
436
437 char __license[] SEC("license") = "GPL";
438
