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#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
// workaround: define induction variable "i" as "long" instead
// of "int" to prevent alu32 sub-register spilling.
#pragma clang loop unroll(disable)
for (long i = 0; i < 100; 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);
}
// Add an Egress TLV fc00::4, add the flag A,
// and apply End.X action to fc42::1
SEC("lwt_seg6local")
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;
}
char __license[] SEC("license") = "GPL";
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