261 lines
6.0 KiB
C
261 lines
6.0 KiB
C
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#include <stddef.h>
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#include <inttypes.h>
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#include <errno.h>
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#include <linux/seg6_local.h>
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#include <linux/bpf.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_endian.h>
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/* Packet parsing state machine helpers. */
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#define cursor_advance(_cursor, _len) \
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({ void *_tmp = _cursor; _cursor += _len; _tmp; })
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#define SR6_FLAG_ALERT (1 << 4)
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#define BPF_PACKET_HEADER __attribute__((packed))
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struct ip6_t {
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unsigned int ver:4;
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unsigned int priority:8;
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unsigned int flow_label:20;
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unsigned short payload_len;
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unsigned char next_header;
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unsigned char hop_limit;
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unsigned long long src_hi;
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unsigned long long src_lo;
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unsigned long long dst_hi;
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unsigned long long dst_lo;
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} BPF_PACKET_HEADER;
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struct ip6_addr_t {
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unsigned long long hi;
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unsigned long long lo;
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} BPF_PACKET_HEADER;
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struct ip6_srh_t {
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unsigned char nexthdr;
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unsigned char hdrlen;
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unsigned char type;
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unsigned char segments_left;
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unsigned char first_segment;
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unsigned char flags;
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unsigned short tag;
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struct ip6_addr_t segments[0];
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} BPF_PACKET_HEADER;
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struct sr6_tlv_t {
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unsigned char type;
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unsigned char len;
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unsigned char value[0];
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} BPF_PACKET_HEADER;
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static __always_inline struct ip6_srh_t *get_srh(struct __sk_buff *skb)
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{
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void *cursor, *data_end;
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struct ip6_srh_t *srh;
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struct ip6_t *ip;
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uint8_t *ipver;
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data_end = (void *)(long)skb->data_end;
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cursor = (void *)(long)skb->data;
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ipver = (uint8_t *)cursor;
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if ((void *)ipver + sizeof(*ipver) > data_end)
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return NULL;
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if ((*ipver >> 4) != 6)
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return NULL;
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ip = cursor_advance(cursor, sizeof(*ip));
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if ((void *)ip + sizeof(*ip) > data_end)
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return NULL;
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if (ip->next_header != 43)
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return NULL;
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srh = cursor_advance(cursor, sizeof(*srh));
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if ((void *)srh + sizeof(*srh) > data_end)
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return NULL;
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if (srh->type != 4)
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return NULL;
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return srh;
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}
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static __always_inline int update_tlv_pad(struct __sk_buff *skb,
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uint32_t new_pad, uint32_t old_pad,
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uint32_t pad_off)
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{
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int err;
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if (new_pad != old_pad) {
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err = bpf_lwt_seg6_adjust_srh(skb, pad_off,
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(int) new_pad - (int) old_pad);
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if (err)
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return err;
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}
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if (new_pad > 0) {
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char pad_tlv_buf[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0};
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struct sr6_tlv_t *pad_tlv = (struct sr6_tlv_t *) pad_tlv_buf;
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pad_tlv->type = SR6_TLV_PADDING;
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pad_tlv->len = new_pad - 2;
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err = bpf_lwt_seg6_store_bytes(skb, pad_off,
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(void *)pad_tlv_buf, new_pad);
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if (err)
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return err;
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}
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return 0;
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}
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static __always_inline int is_valid_tlv_boundary(struct __sk_buff *skb,
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struct ip6_srh_t *srh,
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uint32_t *tlv_off,
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uint32_t *pad_size,
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uint32_t *pad_off)
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{
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uint32_t srh_off, cur_off;
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int offset_valid = 0;
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int err;
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srh_off = (char *)srh - (char *)(long)skb->data;
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// cur_off = end of segments, start of possible TLVs
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cur_off = srh_off + sizeof(*srh) +
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sizeof(struct ip6_addr_t) * (srh->first_segment + 1);
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*pad_off = 0;
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// we can only go as far as ~10 TLVs due to the BPF max stack size
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// workaround: define induction variable "i" as "long" instead
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// of "int" to prevent alu32 sub-register spilling.
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#pragma clang loop unroll(disable)
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for (long i = 0; i < 100; i++) {
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struct sr6_tlv_t tlv;
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if (cur_off == *tlv_off)
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offset_valid = 1;
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if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3))
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break;
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err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv));
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if (err)
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return err;
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if (tlv.type == SR6_TLV_PADDING) {
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*pad_size = tlv.len + sizeof(tlv);
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*pad_off = cur_off;
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if (*tlv_off == srh_off) {
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*tlv_off = cur_off;
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offset_valid = 1;
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}
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break;
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} else if (tlv.type == SR6_TLV_HMAC) {
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break;
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}
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cur_off += sizeof(tlv) + tlv.len;
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} // we reached the padding or HMAC TLVs, or the end of the SRH
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if (*pad_off == 0)
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*pad_off = cur_off;
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if (*tlv_off == -1)
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*tlv_off = cur_off;
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else if (!offset_valid)
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return -EINVAL;
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return 0;
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}
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static __always_inline int add_tlv(struct __sk_buff *skb,
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struct ip6_srh_t *srh, uint32_t tlv_off,
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struct sr6_tlv_t *itlv, uint8_t tlv_size)
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{
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uint32_t srh_off = (char *)srh - (char *)(long)skb->data;
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uint8_t len_remaining, new_pad;
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uint32_t pad_off = 0;
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uint32_t pad_size = 0;
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uint32_t partial_srh_len;
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int err;
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if (tlv_off != -1)
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tlv_off += srh_off;
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if (itlv->type == SR6_TLV_PADDING || itlv->type == SR6_TLV_HMAC)
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return -EINVAL;
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err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
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if (err)
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return err;
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err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len);
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if (err)
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return err;
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err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size);
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if (err)
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return err;
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// the following can't be moved inside update_tlv_pad because the
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// bpf verifier has some issues with it
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pad_off += sizeof(*itlv) + itlv->len;
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partial_srh_len = pad_off - srh_off;
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len_remaining = partial_srh_len % 8;
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new_pad = 8 - len_remaining;
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if (new_pad == 1) // cannot pad for 1 byte only
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new_pad = 9;
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else if (new_pad == 8)
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new_pad = 0;
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return update_tlv_pad(skb, new_pad, pad_size, pad_off);
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}
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// Add an Egress TLV fc00::4, add the flag A,
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// and apply End.X action to fc42::1
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SEC("lwt_seg6local")
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int __add_egr_x(struct __sk_buff *skb)
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{
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unsigned long long hi = 0xfc42000000000000;
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unsigned long long lo = 0x1;
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struct ip6_srh_t *srh = get_srh(skb);
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uint8_t new_flags = SR6_FLAG_ALERT;
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struct ip6_addr_t addr;
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int err, offset;
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if (srh == NULL)
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return BPF_DROP;
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uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
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0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4};
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err = add_tlv(skb, srh, (srh->hdrlen+1) << 3,
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(struct sr6_tlv_t *)&tlv, 20);
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if (err)
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return BPF_DROP;
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offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
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err = bpf_lwt_seg6_store_bytes(skb, offset,
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(void *)&new_flags, sizeof(new_flags));
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if (err)
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return BPF_DROP;
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addr.lo = bpf_cpu_to_be64(lo);
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addr.hi = bpf_cpu_to_be64(hi);
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err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X,
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(void *)&addr, sizeof(addr));
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if (err)
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return BPF_DROP;
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return BPF_REDIRECT;
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}
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char __license[] SEC("license") = "GPL";
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