システム・ソフトウェア
System Software / Operating Systemsオペレーティングシステム

Outline

• Implementing Networking
• Principles概念 of Security
• Relationship Between Networking and Security
• Final Thoughts

Division of Responsibility

What's a Socket? aka Internet Protocol addressing (v4/v6)

Sockets

A socket is the end-point for bidirectional communication通信 flow across a network (or between processプロセスes, but we are interested in the network here). The identifier that makes a unique socket is:

• Local Address (IPv4 or IPv6)
• Local Port number (if ULP is TCP or UDP)
• Remote Address (IPv4 or IPv6)
• Remote Port number (if ULP is TCP or UDP)
• Upper-Layer Protocol identifier (e.g., TCP or UDP)

For Internet services using TCP or UDP, your service name is your port number. Important services use well-known port numbers, assigned by the IANA.

Socket Operation

• Create the socket by calling socket()
• Call bind() to create an address (especially the port number)
• Use listen() to control the number of connections that the socket will support
• accept() a new connection (this creates a new socket for you!)
• Use read() and write() to receive and send data
• shutdown() the connection socket when you're done
• close() the connection socket
• Return to accept() and wait for the next incoming connection

Server Example Code

// Server code in C
// adapted from http://en.wikipedia.org/wiki/Berkeley_sockets
 
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <unistd.h>

int main()
{
  struct addrinfo hint;
  struct sockaddr_storage bindaddr_storage;
  struct sockaddr_in6 *bindaddr6 = 
    (struct sockaddr_in6 *)&bindaddr_storage;
  struct sockaddr_in *bindaddr = 
    (struct sockaddr_in *)&bindaddr_storage;
  struct addrinfo *result;
  struct sockaddr_storage peer;
  int peersize;
  char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
  int retval;

  int i32SocketFD = socket(PF_INET6, SOCK_STREAM, 0);
 
  char msg[] = "Success!\n";

  if(-1 == i32SocketFD)
    {
      perror("can not create socket");
      exit(-1);
    }
  
  bzero(&bindaddr_storage, sizeof(bindaddr_storage));
  bindaddr6->sin6_family = AF_INET6;
  bindaddr6->sin6_addr = in6addr_any;	/* struct assignment */
  bindaddr6->sin6_port = htons(12345);
 
  if(-1 == bind(i32SocketFD,(struct sockaddr*) bindaddr6,
                sizeof(struct addrinfo)))
    {
      printf("error bind failed");
      perror("main");
      exit(-1);
    }
 
  if(-1 == listen(i32SocketFD, 10))
    {
      printf("error listen failed");
      exit(-1);
    }

  // Here, you should print out your local address using
  // getsockname() and getnameinfo() (and gai_strerror on error)

  for(; ;)
    {
      int i32ConnectFD = accept(i32SocketFD, NULL, NULL);
 
      if(0 > i32ConnectFD)
	{
          // improve error reporting here, using perror()
	  printf("error accept failed");
	  exit(-1);
	}


      // Here, you should print out your local address 
      // and the peer address using
      // getsockname(), getpeername(), and getnameinfo()
      // (and gai_strerror on error)

      // perform read write operations ...
      // add error checking and reporting here
      write(i32ConnectFD, msg, sizeof(msg));
      // wait one minute; this lets us see the connection in place, and
      // even see the behavior as we try to start a second connection
      // at the same time
      sleep(60);

      // add error checking and reporting here
      shutdown(i32ConnectFD, 2);
 
      // add error checking and reporting here
      close(i32ConnectFD);
    }
  // add error checking and reporting here
  close(i32SocketFD);
  return 0;
}

Routing Tables (with ARP/Neighbor Cache)

In Linux, as in most Unix systems, the L2 information情報 (the ARP cache, in IPv4 over Ethernet terms, or the Neighbor Cache in IPv6 terms) is kept in the same data structure as the IP routing table. Linux uses a Radix Tree, also known as a Patricia trie.

[rdv@localhost Desktop]$ route -v -A inet 
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
133.27.56.0     *               255.255.248.0   U     0      0        0 ath1
default         gw2-v20.sfc.kei 0.0.0.0         UG    0      0        0 ath1

[rdv@localhost Desktop]$ route -v -A inet6
Kernel IPv6 routing table
Destination                                 Next Hop                                Flags Metric Ref    Use Iface
2001:200:1c0:2000::/64                      *                                       UA    256    104       0 ath1    
fe80::/64                                   *                                       U     256    0        0 ath1    
*/0                                         fe80::213:5fff:fecd:dc00                UGDA  1024   22       0 ath1    
localhost6.localdomain6/128                 *                                       U     0      1        1 lo      
2001:200:1c0:2000:219:7dff:fe0c:f94/128     *                                       U     0      304       1 lo      
fe80::219:7dff:fe0c:f94/128                 *                                       U     0      4        1 lo      
ff02::1/128                                 ff02::1                                 UC    0      6        0 ath1    
ff02::1:ff83:8338/128                       ff02::1:ff83:8338                       UC    0      5        0 ath1    
ff00::/8                                    *                                       U     256    0        0 ath1    

A very common security bug is to allow the caller of a function機能・関数 to present an argument larger than the space allocated for it.

Homeworkかだい

1. Report on your progress on your project.
2. A socket has parts both in the kernel and in the user library. Find the definition of both in an OS of your choice, and describe the differences in the information情報.
3. Write a program that, when run, prints out its own source code.

Readings for Next Week and Followup for This Week

• Yoshfuji's paper on the Linux IPv6 stack
• Radix trees at Wikipedia.
• Stack buffer overflow at Wikipedia.
• NISt Engineering Principles概念 for Information情報 Technology Security (A Baseline for Achieving Security)
• Fedora kernel development wiki
• Mac OS X Security Overview
• Ken Thompson's C compiler hack
• The Robert Morris Internet Worm

その他 Additional Information情報

• Rodney Van Meterのホームページ (home page)
• 村井研究室 Murai Lab