allow superuser to do anything

[unix-history] / usr / src / usr.bin / write / write.c

#ifndef	lint
static char *sccsid = "@(#)write.c	4.10 %G%";
#endif
/*
 * write to another user
 */

#include <stdio.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <signal.h>
#include <utmp.h>
#include <sys/time.h>

#define	NMAX	sizeof(ubuf.ut_name)
#define	LMAX	sizeof(ubuf.ut_line)

char	*strcat();
char	*strcpy();
struct	utmp ubuf;
int	signum[] = {SIGHUP, SIGINT, SIGQUIT, 0};
char	me[NMAX + 1]	= "???";
char	*him;
char	*mytty;
char	histty[32];
char	*histtya;
char	*ttyname();
char	*rindex();
int	logcnt;
int	eof();
int	timout();
FILE	*tf;
char	*getenv();

main(argc, argv)
	int argc;
	char *argv[];
{
	struct stat stbuf;
	register i;
	register FILE *uf;
	int c1, c2;
	long clock = time(0);
	int suser = getuid() == 0;
	struct tm *localtime();
	struct tm *localclock = localtime( &clock );

	if (argc < 2) {
		fprintf(stderr, "Usage: write user [ttyname]\n");
		exit(1);
	}
	him = argv[1];
	if (argc > 2)
		histtya = argv[2];
	if ((uf = fopen("/etc/utmp", "r")) == NULL) {
		perror("write: Can't open /etc/utmp");
		goto cont;
	}
	mytty = ttyname(2);
	if (mytty == NULL) {
		fprintf(stderr, "write: Can't find your tty\n");
		exit(1);
	}
	if (stat(mytty, &stbuf) < 0) {
		perror("write: Can't stat your tty");
		exit(1);
	}
	if (!suser && (stbuf.st_mode&02) == 0) {
		fprintf(stderr,
			"write: You have write permission turned off\n");
		exit(1);
	}
	mytty = rindex(mytty, '/') + 1;
	if (histtya) {
		strcpy(histty, "/dev/");
		strcat(histty, histtya);
	}
	while (fread((char *)&ubuf, sizeof(ubuf), 1, uf) == 1) {
		if (ubuf.ut_name[0] == '\0')
			continue;
		if (strcmp(ubuf.ut_line, mytty)==0) {
			for (i=0; i<NMAX; i++) {
				c1 = ubuf.ut_name[i];
				if (c1 == ' ')
					c1 = 0;
				me[i] = c1;
				if (c1 == 0)
					break;
			}
		}
		if (him[0] == '-' && him[1] == 0)
			goto nomat;
		for (i=0; i<NMAX; i++) {
			c1 = him[i];
			c2 = ubuf.ut_name[i];
			if (c1 == 0)
				if (c2 == 0 || c2 == ' ')
					break;
			if (c1 != c2)
				goto nomat;
		}
		logcnt++;
		if (histty[0]==0) {
			strcpy(histty, "/dev/");
			strcat(histty, ubuf.ut_line);
		}
	nomat:
		;
	}
cont:
	if (logcnt==0 && histty[0]=='\0') {
		fprintf(stderr, "write: %s not logged in\n", him);
		exit(1);
	}
	if (uf != NULL)
		fclose(uf);
	if (histtya==0 && logcnt > 1) {
		fprintf(stderr,
		"write: %s logged in more than once ... writing to %s\n",
			him, histty+5);
	}
	if (histty[0] == 0) {
		printf(him);
		if (logcnt)
			printf(" not on that tty\n"); else
			printf(" not logged in\n");
		exit(1);
	}
	if (access(histty, 0) < 0) {
		fprintf(stderr, "write: No such tty\n");
		exit(1);
	}
	signal(SIGALRM, timout);
	alarm(5);
	if ((tf = fopen(histty, "w")) == NULL)
		goto perm;
	alarm(0);
	if (fstat(fileno(tf), &stbuf) < 0)
		goto perm;
	if (!suser && (stbuf.st_mode&02) == 0)
		goto perm;
	sigs(eof);
	{ char hostname[32];
	  gethostname(hostname, sizeof (hostname));
	  fprintf(tf,
	      "\r\nMessage from %s@%s on %s at %d:%02d ...\r\n\007\007\007",
	      me, hostname, mytty, localclock->tm_hour, localclock->tm_min);
	fflush(tf);
	}
	for (;;) {
		char buf[BUFSIZ];
		register char *bp;
		i = read(0, buf, sizeof buf);
		if (i <= 0)
			eof();
		if (buf[0] == '!') {
			buf[i] = 0;
			ex(buf);
			continue;
		}
		for (bp = buf; --i >= 0; bp++) {
			if (*bp == '\n')
				putc('\r', tf);

			if (!isascii(*bp)) {
				putc('M', tf);
				putc('-', tf);
				*bp = toascii(*bp);
			}

			if (isprint(*bp) ||
			    *bp == ' ' || *bp == '\t' || *bp == '\n') {
				putc(*bp, tf);
			} else {
				putc('^', tf);
				putc(*bp ^ 0100, tf);
			}

			if (*bp == '\n')
				fflush(tf);

			if (ferror(tf) || feof(tf)) {
				printf("\n\007Write failed (%s logged out?)\n",
					him);
				exit(1);
			}
		}
	}
perm:
	fprintf(stderr, "write: Permission denied\n");
	exit(1);
}

timout()
{

	fprintf(stderr, "write: Timeout opening their tty\n");
	exit(1);
}

eof()
{

	fprintf(tf, "EOF\r\n");
	exit(0);
}

ex(bp)
	char *bp;
{
	register i;

	sigs(SIG_IGN);
	i = fork();
	if (i < 0) {
		printf("Try again\n");
		goto out;
	}
	if (i == 0) {
		sigs((int (*)())0);
		execl(getenv("SHELL") ?
		    getenv("SHELL") : "/bin/sh", "sh", "-c", bp+1, 0);
		exit(0);
	}
	while (wait((int *)NULL) != i)
		;
	printf("!\n");
out:
	sigs(eof);
}

sigs(sig)
	int (*sig)();
{
	register i;

	for (i=0; signum[i]; i++)
		signal(signum[i], sig);
}