dave@utcsrgv.UUCP (Dave Sherman) (01/06/84)
I have had a number of requests to post my source to the programs
for flipping a telephone line from dialin to dialout and vice versa.
It's a little more sophisticated (and faster) than a shell file which
edits /etc/ttys. Below are two files, originate.c and answer.c.
Some limitations to note:
1. The programs assume you have only one telephone line. You'll
have to change the #define from tty7 to whatever you need.
2. SIGINT is assumed to be the signal to restart init. Some
versions of UNIX use SIGHUP. Also, some systems have a
different name for the file than /etc/ttys.
3. **IMPORTANT** The programs assume that the phone line is the
first entry in ttys. If you have no reason not to, edit your
ttys by hand and move the phone line to the top. (The only
noticeable effect will be that a login on the phone line
will be the first one shown when you run "who".) Otherwise,
change the programs to search for the correct line.
4. By convention, anyone who uses the line for dialout should
ioctl it to TIOCEXCL (exclusive use). Although root can break
through, originate and answer fork off and setuid(1) to inhibit
this, so the TIOCEXCL setting will stop any attempts at switching
the line. You might want to check that your version of cu, tip
or whatever you use to call-out-as-a-terminal does the ioctl.
Uucico does it properly.
That's it. Compile the programs and make them setuid to root.
=================================================================
/*
* ORIGINATE
*
* Set the telephone line for dial-out
*
* Dave Sherman, April 1983
* The Law Society of Upper Canada
* utcsrgv!lsuc!dave (also utcsrgv!dave at U of Toronto)
*/
#define TTYS "/etc/ttys"
#define UTMP "/etc/utmp"
#define INIT 1 /* process ID of /etc/init process */
char dialout[] = "tty7";
#define SOMEONE_ON 1
#define NOONE_ON 0
#include <signal.h>
#include <stdio.h>
#include <utmp.h>
#include <sgtty.h>
main()
{
register ttys;
char c;
/* first look at /etc/ttys, to see if the
* line is already in originate mode. Convention
* is that anyone who changes ttys should run
* the "kill -2 1" immediately.
* By convention, the telephone line should be the
* first one in the ttys file.
* Once we see it was in answer mode, check that
* that line isn't being used. Then send it a
* "stty hup" to kick off any modem that's sitting
* on the line, update /etc/ttys and send the
* /etc/init process (PID 1) the reinitialization
* signal, so it will kick getty off the line
*/
ttys = open(TTYS, 2);
if(ttys < 0)
{
perror("originate: open ttys");
exit(1);
}
if(read(ttys, &c, 1) != 1)
{
perror("originate: read from ttys");
exit(1);
}
switch(c)
{
case '0':
printf("line is already in originate mode\n");
return(0);
case '1':
checkout(ttys);
if(checkline(dialout) == SOMEONE_ON)
{
printf("Can't originate - someone is logged in on %s!\n", dialout);
exit(1);
}
sendhup(dialout);
orig(ttys);
close(ttys);
if(kill(INIT, SIGINT)) /* non-zero */
{
perror("originate: couldn't kill process 1");
exit(1);
}
return(0);
default:
printf("ttys file (%s) has bad format\n", TTYS);
exit(1);
}
}
checkout(fd)
register fd;
{
/* check that the next few chars of the /etc/ttys
* file match the "dialout" string. Skip the first
* char, which is the speed code and irrelevant.
*/
char buf1[30], buf2[30];
register n;
/* read the speed code and the newline, too */
n = strlen(dialout) + 2;
if(read(fd, buf1, n) != n)
{
perror("originate: read from /etc/ttys");
exit(1);
}
buf1[n] = 0; /* mark end of string */
sprintf(buf2, "%s\n", dialout);
/* now compare the strings */
if(strcmp(buf1+1, buf2))
{
printf("First line in /etc/ttys ('1%s') doesn't match dialout line ('%s')\n", buf1, buf2);
exit(1);
}
/* just return happily */
}
checkline(dialout)
register char *dialout;
{
char buf[30];
/* check that the line doesn't have anyone logged in
* at the moment, so we can use it for originating
* a call
*/
struct utmp utmp;
register FILE *fp;
fp = fopen(UTMP, "r");
if(fp == NULL)
{
perror("can't open utmp");
exit(1);
}
while(!feof(fp) && !ferror(fp))
{
fread(&utmp, sizeof utmp, 1, fp);
if(utmp.ut_name[0] && !strcmp(utmp.ut_line, dialout))
return(SOMEONE_ON);
}
return(NOONE_ON);
}
sendhup(line)
register char *line;
{
char buf[30];
register fd;
register pid;
int status;
sprintf(buf, "/dev/%s", line);
chmod(buf, 0666);
/* go through some contortions here. We have to check
* for TIOCEXCL while we are not root, since root is
* allowed to break in. But we have to keep running later
* as root. So fork off a copy of ourselves to do the
* checking.
*/
if((pid=fork()) == -1)
{
perror("can't fork");
exit(1);
}
if(pid == 0) /* child */
{
setuid(1); /* ==daemon, non-root */
if((fd = open(buf, 1)) < 0)
{
printf("can't open %s to send hangup signal\n", buf);
exit(1);
}
ioctl(fd, TIOCHPCL, NULL);
exit(0);
}
wait(&status);
if(status) /* exit(1) above */
exit(1);
}
orig(fd)
register fd;
{
/* change the first byte in the file to be a '0',
* so getty won't start up a login for that line
*/
long lseek();
if(lseek(fd, 0L, 0) != 0L)
{
perror("originate: lseek failed");
exit(1);
}
if(write(fd, "0", 1) != 1)
{
perror("originate: writing to /etc/ttys");
exit(1);
}
}
=================================================================
/*
* ANSWER
*
* Set the telephone line for dial-in
*
* Dave Sherman, April 1983
* The Law Society of Upper Canada
* utcsrgv!lsuc!dave (also utcsrgv!dave at U of Toronto)
*/
#define TTYS "/etc/ttys"
#define INIT 1 /* process ID of /etc/init process */
char dialout[] = "tty7";
#include <signal.h>
#include <stdio.h>
#include <sgtty.h>
main()
{
register ttys;
char c;
/* first look at /etc/ttys, to see if the
* line is already in answer mode. Convention
* is that anyone who changes ttys should run
* the "kill -2 1" immediately.
* By convention, the telephone line should be the
* first one in the ttys file.
* Once we see it was in originate mode, check that
* that line isn't being used. Then send it a
* "stty hup" to kick off any modem that's sitting
* on the line, update /etc/ttys and send the
* /etc/init process (PID 1) the reinitialization
* signal, so it will put a getty on the line
*/
ttys = open(TTYS, 2);
if(ttys < 0)
{
perror("answer: open ttys");
exit(1);
}
if(read(ttys, &c, 1) != 1)
{
perror("answer: read from ttys");
exit(1);
}
switch(c)
{
case '1':
printf("line is already in answer mode\n");
return(0);
case '0':
checkout(ttys);
if(lineopen(dialout))
{
printf("Can't answer - someone is using line %s!\n", dialout);
exit(1);
}
sendhup(dialout);
answ(ttys);
close(ttys);
if(kill(INIT, SIGINT)) /* non-zero */
{
perror("answer: couldn't kill process 1");
exit(1);
}
return(0);
default:
printf("ttys file (%s) has bad format\n", TTYS);
exit(1);
}
}
checkout(fd)
register fd;
{
/* check that the next few chars of the /etc/ttys
* file match the "dialout" string. Skip the first
* char, which is the speed code and irrelevant.
*/
char buf1[30], buf2[30];
register n;
/* read the speed code and the newline, too */
n = strlen(dialout) + 2;
if(read(fd, buf1, n) != n)
{
perror("answer: read from /etc/ttys");
exit(1);
}
buf1[n] = 0; /* mark end of string */
sprintf(buf2, "%s\n", dialout);
/* now compare the strings */
if(strcmp(buf1+1, buf2))
{
printf("First line in /etc/ttys ('0%s') doesn't match buf2 line ('%s')\n", buf1, dialout);
exit(1);
}
/* just return happily */
}
sendhup(line)
register char *line;
{
char buf[30];
register fd;
sprintf(buf, "/dev/%s", line);
chmod(buf, 0666);
if((fd = open(buf, 1)) < 0)
{
printf("can't open %s to send hangup signal\n", buf);
return;
}
ioctl(fd, TIOCHPCL, NULL);
}
answ(fd)
register fd;
{
/* change the first byte in the file to be a '1',
* so getty will start up a login for that line
*/
long lseek();
if(lseek(fd, 0L, 0) != 0L)
{
perror("answer: lseek failed");
exit(1);
}
if(write(fd, "1", 1) != 1)
{
perror("answer: writing to /etc/ttys");
exit(1);
}
}
lineopen(line)
register char *line;
{
register fd;
register pid;
int status;
char buffer[30];
sprintf(buffer, "/dev/%s", line);
/* see if we can open the line - programs that use it
* will ioctl(line, TIOCEXCL, 0) by convention
*/
if((pid=fork()) == -1)
{
printf("can't fork");
exit(1);
}
if(pid == 0)
{
setuid(1); /* so TIOCEXCL will work */
if((fd=open(buffer, 0))< 0)
exit(1);
close(fd);
exit(0);
}
wait(&status);
if(status)
return(1); /* bad */
return(0); /* good */
}
--
{allegra,cornell,decvax,ihnp4,linus,utzoo}!utcsrgv!dave