Raw Socket recvfrom not working for TCP

Raw Socket recvfrom not working for TCP

This is not going to work on any BSD Sockets implementation. You can’t use raw sockets to read TCP or UDP. To quote my trusty (and dusty, literally!) copy of Stevens [1]:

The following rules apply;

1. Received UDP packets and received TCP packets are never [their emphasis] passed to a raw socket.

This is UNIX Network Programming, Volume 1, Second Edition, section 25.4 Raw Socket Input, page 659.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

[1] http://www.unpbook.com

Hi @eskimo, This book is really helpful. Thank you.

There is one more point under Raw Socket Input:

• All IP datagrams with a protocol field that the kernel does not understand are passed to a raw socket. The only kernel processing done on these packets is the minimal verification of some IP header fields: the IP version, IPv4 header checksum, header length, and destination IP address (pp. 213–220 of TCPv2).

is there any workaround that we can do with ip packet during sendto so that kernel does not understand and passes to raw socket?

is there any workaround that we can do with ip packet during sendto so that kernel does not understand and passes to raw socket?

I’m not sure what you’re asking for here. Can you take a step back and explain your high-level goal?

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Can you take a step back and explain your high-level goal?

I am getting NEPacket via Packet tunnel provider System extension. I need to forward this packet to server Which will re-injected this ip packet into network stack after processing. Since raw socket can't be opened by system extension due to sandbox restriction, i am reading IP packet in separate process via BSD Packet Filter(BPF) - read(bpf, bpfBuffer, bufLength);

After receiving IP Packet at the bpf end, I am using raw socket to send it to server. sendto is working fine, its getting receive at server end. recvfrom is failing. For ICMP, both sendto and recvfrom is working fine.

Please let me know if any other ways to achieve this?

FYI Following code working fine on linux, but not working on mac.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main(void) {
  int i, recv_length, sockfd;

  u_char buffer[9000];

  printf("Opening socket\n");
  if ((sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_TCP)) == -1) {
    printf("Socket failed!!\n");

    return -1;
  }
  printf("Socket opened\n");

  for(i=0; i < 3; i++) {
   printf("Going to read i: %d\n", i);
   recv_length = recv(sockfd, buffer, 8000, 0);
   printf("Got some bytes : %d\n", recv_length);
  }

  return 0;
}

Following code working fine on linux

It’s called BSD Sockets for a reason (-:

Please let me know if any other ways to achieve this?

Nothing good springs to mind.

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"