xdp-project-bpf-examples/pping/pping_helpers.h

#ifndef PPING_HELPERS_H
#define PPING_HELPERS_H

#include "pping.h"
#define MAX_TCP_OPTIONS 10

static __always_inline int fill_ipv4_flow(struct ipv4_flow *flow, __u32 saddr, __u32 daddr, __u16 sport, __u16 dport)
{
  flow->saddr = saddr;
  flow->daddr = daddr;
  flow->sport = sport;
  flow->dport = dport;
  return 0;
}

// Parses the TSval and TSecr values from the TCP options field - returns 0 if sucessful and -1 on failure
// If sucessful the TSval and TSecr values will be stored at tsval and tsecr (in network byte order!)
static __always_inline int parse_tcp_ts(struct tcphdr *tcph, void *data_end, __u32 *tsval, __u32 *tsecr)
{
  if (tcph + 1 > data_end) // To hopefully please verifier
    return -1;
  int len = tcph->doff << 2;
  if (len <= sizeof(struct tcphdr)) // No TCP options
    return -1;
  void *pos = (void *)(tcph + 1);
  void *opt_end = ((void *)tcph + len);
  __u8 i, opt, opt_size;
  #pragma unroll
  for (i = 0; i < MAX_TCP_OPTIONS; i++) {
    if (pos+1 > opt_end || pos+1 > data_end)
      return -1;
    opt = *(__u8 *)pos; // Save value to variable so I don't have to perform any more data_end checks on the option kind
    if (opt == 0) // Reached end of TCP options
      return -1;
    if (opt == 1) {// TCP NOP option - advance one byte
	pos++;
	continue;
      }
    // Option > 1, should have option size
    if (pos+2 > opt_end || pos+2 > data_end)
      return -1;
    opt_size = *(__u8 *)(pos+1); // Save value to variable so I don't have to perform any more data_end checks on option size

    if (opt == 8 && opt_size == 10) { // Option-kind is TCP timestap (yey!)
      if (pos + opt_size > opt_end || pos + opt_size > data_end)
	return -1;
      *tsval = *(__u32 *)(pos + 2);
      *tsecr = *(__u32 *)(pos + 6);
      return 0;
    }

    // Some other TCP option - advance option-length bytes
    pos += opt_size;
  }
  return -1;
}

#endif