Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!rutgers!cmcl2!brl-adm!umd5!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.sources.bugs
Subject: Re: Problem in Dan Heller's "dots" game
Message-ID: <9982@mimsy.UUCP>
Date: 30 Dec 87 20:33:06 GMT
References: <7765@eddie.MIT.EDU>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 88

In article <7765@eddie.MIT.EDU>, billw@oberon.lcs.mit.edu (Bill Wisner) writes:
>Due to a problem with the format of /etc/utmp, dots can't handle 2-player
>games against someone with an eight-letter username. The following replacement
>for findem.c alleviates the problem.

As it says in <utmp.h>, `Assuming the number 8 is unwise.'  There are
several other potential bugs in this routine (I spotted three offhand).
I would change it to something more like this:

/* findem.c   find the login of the person we wanna play */

#include "dots.h"
#include <sys/stat.h>
#include <sgtty.h>
#include <utmp.h>

#define UTMP  		"/etc/utmp"

struct utmp utmp_buf;
struct stat stat_buf;
struct sgttyb sgtty_buf;

int fd;

#define	NMAX	sizeof(utmp_buf.ut_name)
#define	LMAX	sizeof(utmp_buf.ut_line)
#define	DEVPART	"/dev/"
#define	DEVLEN	5		/* strlen(DEVPART) */

char	*ttyname();

findem(argc, argv)
	int argc;
	char **argv;
{
	register char *login = argv[2], *where = 0, *ourtty = ttyname(0);
	register FILE *recipient;
	int found;
	char *to_tty[DEVLEN + LMAX + 1];

	if (ourtty == 0) {
		fprintf(stderr, "%s: can't find your tty\n");
		return 0;
	}
	ourtty += DEVLEN;
	if (argc > 3) {
		where = argv[3];
		if (strcmp(where, ourtty) == 0) {
			fprintf(stderr, "You can't play yourself.\n");
			return 0;
		}
	}
	if ((fd = open(UTMP, 0)) == -1) {
		perror(UTMP);
		return 0;
	}
	found = 0;
	while (read(fd, (char *)&utmp_buf, sizeof(utmp_buf)) > 0) {
		if (strncmp(utmp_buf.ut_name, login, NMAX) != 0)
			continue;
		found = -1;
		if (where == 0 ||
		    strncmp(utmp_buf.ut_line, where, LMAX) == 0)) {
			found = 1;
			break;
		}
	}
	(void) close(fd);
	if (found < 1) {
		fprintf(stderr, "%s is not logged in%s%s.\n", login,
			found ? " on " : "", found ? where : "");
		return 0;
	}
	/* N.B.: %.*s may be dubious under dpANS */
	(void) sprintf(to_tty, "%s%.*s", DEVPART, LMAX, utmp_buf.ut_line);
	if ((recipient = fopen(to_tty, "w")) == 0) {
		perror(to_tty);
		fprintf(stderr, "%s: Can't ask %s to play.\n", argv[0],
			argv[2]);
		return 0;
	}
	setgid(getgid());/* probably isn't necessary most of the time */
	setuid(getuid());/* turns off set-uid attribute once tty is opened */

	return invite(recipient);
}
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris