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From: ron@topaz.rutgers.edu (Ron Natalie)
Newsgroups: comp.unix.wizards
Subject: Re: Pseudo-tty ownership problem
Message-ID: <15300@topaz.rutgers.edu>
Date: Sun, 4-Oct-87 14:38:54 EDT
Article-I.D.: topaz.15300
Posted: Sun Oct  4 14:38:54 1987
Date-Received: Wed, 7-Oct-87 06:23:31 EDT
References: <730@quacky.UUCP> <6503@brl-smoke.ARPA>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 87

Enclosed... A program that when made setuid root allows a user who
is so authorized to chown a pty to himself and free it up later.
I needed this for when I added user mode attach/detach to UNIX.
This program must be called with the open control side of the PTY
as file descriptor 0 (to prove that the user has passed the kernel
restrictions on who can use the pty) and the name of the PTY.
There was code to create a UTMP entry for the pty (-u) and delete
the utmp entry when done, but I've removed that as it was shamelessly
stolen from some other program which is probably under license
(I think it was login).
--- Cut Here ---
#include <sys/types.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/file.h>

char	*filename = "/dev/ptyxx";

main(argc, argv)
	int	argc;
	char	**argv;
{
	int	i;
	int	foo = 0;
	int	aflag = 0;
	int	dflag = 0;
	int	uflag = 0;
	char	*ptyname = 0;


	struct	stat	statf, statd;

	while(--argc)  {
		++argv;
		if(*argv[0] == '-')  {
			if(argv[0][1] == 'a')
				aflag++;
			if(argv[0][1] == 'd')
				dflag++;
			if(argv[0][1] == 'u')
				uflag++;
		} else
			ptyname = *argv;
	}

	if( (aflag + dflag) != 1  || (ptyname == 0))  {
		fprintf(stderr, "Usage:  pty {-a or -d} ptycontrol\n");
		exit(1);
	}
	filename[8] = ptyname[0];
	filename[9] = ptyname[1];
	
	if(stat(filename, &statd) == -1)  {
		perror(filename);
		exit(2);
	}
	if(fstat(0, &statf) == -1)  {
		perror("std in");
		exit(3);
	}
	if(( statd.st_mode&S_IFMT) != S_IFCHR)  {
		fprintf(stderr, "%s: not a pty\n", filename);
		exit(4);
	}
	if(( statf.st_mode&S_IFMT) != S_IFCHR)  {
		fprintf(stderr, "std in: not a pty\n");
		exit(5);
	}
	if(statf.st_rdev != statd.st_rdev)  {
		fprintf(stderr, "std in does not match pty controller\n");
		exit(6);
	}
	filename[5] = 't';
	
	if(aflag)  {
		chmod(filename, 0611);
		i = chown(filename, getuid(), getgid());
	}
	if(dflag)  {
		rmut();
	}
	if(i == -1)  {
		perror(filename);
		exit(7);
	}
	exit(0);
}