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Date: Sat, 26 Jan 2002 23:51:38 -0500
To: Corinna Vinschen <cygwin AT cygwin DOT com>
From: "Pierre A. Humblet" <Pierre DOT Humblet AT ieee DOT org>
Subject: Re: socket/fdopen/exec problem
Cc: cygwin <cygwin AT cygwin DOT com>
In-Reply-To: <20020125171021.X11608@cygbert.vinschen.de>
References: <3C517C32 DOT BB66DB47 AT ieee DOT org>
 <3C50520B DOT 3239FAC5 AT ieee DOT org>
 <20020124220339 DOT K11608 AT cygbert DOT vinschen DOT de>
 <3C5080F8 DOT 4E4B8945 AT ieee DOT org>
 <20020125105955 DOT P11608 AT cygbert DOT vinschen DOT de>
 <3C517C32 DOT BB66DB47 AT ieee DOT org>
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At 05:10 PM 1/25/02 +0100, Corinna Vinschen wrote:
>On Fri, Jan 25, 2002 at 10:39:30AM -0500, Pierre A. Humblet wrote:

<snip, long example>
>> Any thoughts?
>
>Not immediately.  Two questions:
>
<snip, already answered>

>- Could you patch Cygwin fhandler_socket.cc, fhandler_socket::close()
>  and rip out the whole linger stuff so that only the naked closesocket()
>  call remains and see if that changes the behaviour?
>
Corinna,

No difference (on Win98 and Me. I will try NT on Monday).

I can now duplicate exactly what's happening in the application I am porting.
A key element is that it disconnects itself from the controlling terminal
by closing fd 0, 1 & 2 and forking. Weird things happen afterwards:
1) For every re-exec (triggered by -HUP), ps -W and the Windows task manager
   show an extra copy of the program.
   [without the disconnect from the controlling terminal, only one process
appears]
2) If a tcp call was received and a child was forked, then after the next
re-exec
   netstat -a shows an extra LISTEN on port 999. It never goes away. This
happens
   even if the -HUP is given long after (I tried up to 5 minutes) the child
   terminates. Eventually incoming calls are not answered.
   [without the disconnect from the controlling terminal, an extra LISTEN
appears 
    only if the -HUP was given while the child is running, and it
disappears when 
    the child exits]
I have no idea where to start debugging that. I am attaching the demo program.
It is used as shown in the previous message, and also using ps -W. 

Ntsec good news: I think I have identified and solved the problem of
having an incorrect UID, and also of setting the DACL in the token security
descriptor. I will test on Monday and let you know.

Pierre
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Content-Disposition: attachment; filename="tcpdemo.c"

/**********************************************
 *
 This demo program exposes a bug where there
 are to listen on the same tcp port.
 New connections may or may not be accepted=
 

**********************************************/
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <signal.h>
#include <netinet/in.h>
#include <unistd.h>

enum {FALSE, TRUE};

/*************************************************
*             SIGHUP Handler                    =
 *
*************************************************/
static int sighup_seen;

static void
sighup_handler(int sig)
{
sig =3D sig;    /* Keep picky compilers happy */
sighup_seen =3D TRUE;
signal(SIGHUP, sighup_handler);
}

main(int argc, char * argv[])
{
  int on =3D 1, sockfd, newsockfd, lcount, peer_size;
  int status, cpid, pid;
  struct sockaddr_in addr, peer;
  fd_set select_listen;
  FILE *fd;
  char msg[100];
//  struct linger linger;
//  linger.l_onoff =3D 1;
//  linger.l_linger =3D 0;

#if 1
  close(0);
  close(1);
  close(2);
  pid =3D 0;
  if (getppid() !=3D 1) {   /* not a re-exec */
	  unlink("demo.log"); /* old log */
	  pid =3D fork();
	  if (pid > 0) exit(EXIT_SUCCESS);   /* in parent process, just exit */
//	  setsid();    
  }
#endif
  fd =3D fopen("demo.log", "a");
  if (pid < 0) {
	  fprintf(fd, "Fork: %s\n", strerror(errno));
	  exit(1);
  }

  /************************************************
   *
   Open a socket and listen on port 999

  ************************************************/

  sockfd =3D socket(AF_INET, SOCK_STREAM, 0);
  if (sockfd < 0) 
	fprintf(fd, "socket: %s\n", strerror(errno));

  if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) <=
 0)
	fprintf(fd, "setsockopt: %s\n", strerror(errno));
  if (setsockopt(sockfd, SOL_SOCKET, TCP_NODELAY, &on, sizeof(on)) < 0)
	  fprintf(fd, "setsockopt: %s\n", strerror(errno));
//  if (setsockopt(sockfd, SOL_SOCKET, SO_LINGER, (const char *)&linger,=
 sizeof linger) < 0)
//	  fprintf(fd, "setsockopt: %s\n", strerror(errno));
  memset(&addr, 0, sizeof(addr));
  addr.sin_family =3D AF_INET;
  addr.sin_port =3D htons(999);
  addr.sin_addr.s_addr =3D INADDR_ANY;
  if (bind(sockfd, (struct sockaddr *) &addr, sizeof(addr)) <=
 0)
	fprintf(fd, "bind: %s\n", strerror(errno));
  
  if (listen(sockfd, 10) < 0) 
	fprintf(fd, "listen: %d %s\n", errno, strerror(errno));
 
  sighup_seen =3D FALSE;
  signal(SIGHUP, sighup_handler);
  pid =3D getpid();

  /************************************************
   *
   Now wait for a call or sighup, causing a re-exec
   After a re-exec following a call, there are two
   listen on port 999 (netstat -a)
   Incoming calls may or may not work.
   
  ************************************************/

  while(1) {
	FD_ZERO(&select_listen);
	FD_SET(sockfd, &select_listen);
	fprintf(fd, "looping pid %d\n", pid);
	lcount =3D select(sockfd + 1, &select_listen, NULL, NULL, NULL);
	if (lcount =3D=3D 1) {
	  peer_size =3D sizeof(peer);
	  newsockfd =3D accept(sockfd, (struct sockaddr *) &peer, &peer_size);
	  if (newsockfd < 0) {
		fprintf(fd, "accept: %s\n", strerror(errno));
	  }
	  else {
		fprintf(fd, "Got a call\n");
		fflush(fd);
		if ((cpid =3D fork()) =3D=3D 0) {
		  signal(SIGHUP, SIG_IGN);
		  close(sockfd);
		  sprintf(msg, "Hello world. Type kill -HUP %d\n", pid);
		  write(newsockfd, msg, strlen(msg));
		  /* In this demo we sleep, in reality the child is working */
		  sleep(60);
		  fprintf(fd, "Child exiting\n");
		  fclose(fd);
		  close(newsockfd);
		  exit(0);
		}
		else if (cpid > 0) {
		  fprintf(fd, "Process %d started\n", cpid);
		  close(newsockfd);
		}
		else fprintf(fd, "Fork %s\n", strerror(errno));
	  }
	}
	else if (sighup_seen =3D=3D TRUE) {
	  fprintf(fd, "Sighup seen. Execing\n");
	  fclose(fd);
	  close(sockfd);
	  signal(SIGHUP, SIG_IGN);
	  execv(argv[0], argv);
	}
	else fprintf(fd, "Select error %s\n", strerror(errno));
	fflush(fd);
  }
}


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