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/* 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
 17struct 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
 30struct ip6_addr_t {
 31	unsigned long long hi;
 32	unsigned long long lo;
 33} BPF_PACKET_HEADER;
 34
 35struct 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
 47struct sr6_tlv_t {
 48	unsigned char type;
 49	unsigned char len;
 50	unsigned char value[0];
 51} BPF_PACKET_HEADER;
 52
 53static __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
 87static __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
117static __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	#pragma clang loop unroll(disable)
136	for (int i = 0; i < 100; i++) {
137		struct sr6_tlv_t tlv;
138
139		if (cur_off == *tlv_off)
140			offset_valid = 1;
141
142		if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3))
143			break;
144
145		err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv));
146		if (err)
147			return err;
148
149		if (tlv.type == SR6_TLV_PADDING) {
150			*pad_size = tlv.len + sizeof(tlv);
151			*pad_off = cur_off;
152
153			if (*tlv_off == srh_off) {
154				*tlv_off = cur_off;
155				offset_valid = 1;
156			}
157			break;
158
159		} else if (tlv.type == SR6_TLV_HMAC) {
160			break;
161		}
162
163		cur_off += sizeof(tlv) + tlv.len;
164	} // we reached the padding or HMAC TLVs, or the end of the SRH
165
166	if (*pad_off == 0)
167		*pad_off = cur_off;
168
169	if (*tlv_off == -1)
170		*tlv_off = cur_off;
171	else if (!offset_valid)
172		return -EINVAL;
173
174	return 0;
175}
176
177static __always_inline int add_tlv(struct __sk_buff *skb,
178				   struct ip6_srh_t *srh, uint32_t tlv_off,
179				   struct sr6_tlv_t *itlv, uint8_t tlv_size)
180{
181	uint32_t srh_off = (char *)srh - (char *)(long)skb->data;
182	uint8_t len_remaining, new_pad;
183	uint32_t pad_off = 0;
184	uint32_t pad_size = 0;
185	uint32_t partial_srh_len;
186	int err;
187
188	if (tlv_off != -1)
189		tlv_off += srh_off;
190
191	if (itlv->type == SR6_TLV_PADDING || itlv->type == SR6_TLV_HMAC)
192		return -EINVAL;
193
194	err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
195	if (err)
196		return err;
197
198	err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len);
199	if (err)
200		return err;
201
202	err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size);
203	if (err)
204		return err;
205
206	// the following can't be moved inside update_tlv_pad because the
207	// bpf verifier has some issues with it
208	pad_off += sizeof(*itlv) + itlv->len;
209	partial_srh_len = pad_off - srh_off;
210	len_remaining = partial_srh_len % 8;
211	new_pad = 8 - len_remaining;
212
213	if (new_pad == 1) // cannot pad for 1 byte only
214		new_pad = 9;
215	else if (new_pad == 8)
216		new_pad = 0;
217
218	return update_tlv_pad(skb, new_pad, pad_size, pad_off);
219}
220
221// Add an Egress TLV fc00::4, add the flag A,
222// and apply End.X action to fc42::1
223SEC("lwt_seg6local")
224int __add_egr_x(struct __sk_buff *skb)
225{
226	unsigned long long hi = 0xfc42000000000000;
227	unsigned long long lo = 0x1;
228	struct ip6_srh_t *srh = get_srh(skb);
229	uint8_t new_flags = SR6_FLAG_ALERT;
230	struct ip6_addr_t addr;
231	int err, offset;
232
233	if (srh == NULL)
234		return BPF_DROP;
235
236	uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
237			   0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4};
238
239	err = add_tlv(skb, srh, (srh->hdrlen+1) << 3,
240		      (struct sr6_tlv_t *)&tlv, 20);
241	if (err)
242		return BPF_DROP;
243
244	offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
245	err = bpf_lwt_seg6_store_bytes(skb, offset,
246				       (void *)&new_flags, sizeof(new_flags));
247	if (err)
248		return BPF_DROP;
249
250	addr.lo = bpf_cpu_to_be64(lo);
251	addr.hi = bpf_cpu_to_be64(hi);
252	err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X,
253				  (void *)&addr, sizeof(addr));
254	if (err)
255		return BPF_DROP;
256	return BPF_REDIRECT;
257}
258char __license[] SEC("license") = "GPL";

  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
 17struct 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
 30struct ip6_addr_t {
 31	unsigned long long hi;
 32	unsigned long long lo;
 33} BPF_PACKET_HEADER;
 34
 35struct 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
 47struct sr6_tlv_t {
 48	unsigned char type;
 49	unsigned char len;
 50	unsigned char value[0];
 51} BPF_PACKET_HEADER;
 52
 53static __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
 87static __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
117static __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
179static __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
225SEC("lwt_seg6local")
226int __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}
260char __license[] SEC("license") = "GPL";