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/* $OpenBSD: sshpty.c,v 1.34 2019/07/04 16:20:10 deraadt Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
* All rights reserved
* Allocating a pseudo-terminal, and making it the controlling tty.
*
* As far as I am concerned, the code I have written for this software
* can be used freely for any purpose. Any derived versions of this
* software must be clearly marked as such, and if the derived work is
* incompatible with the protocol description in the RFC file, it must be
* called by a name other than "ssh" or "Secure Shell".
*/
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <grp.h>
#include <paths.h>
#include <pwd.h>
#include <stdarg.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
#include <util.h>
#include "sshpty.h"
#include "log.h"
#ifndef O_NOCTTY
#define O_NOCTTY 0
#endif
/*
* Allocates and opens a pty. Returns 0 if no pty could be allocated, or
* nonzero if a pty was successfully allocated. On success, open file
* descriptors for the pty and tty sides and the name of the tty side are
* returned (the buffer must be able to hold at least 64 characters).
*/
int
pty_allocate(int *ptyfd, int *ttyfd, char *namebuf, size_t namebuflen)
{
char buf[64];
int i;
i = openpty(ptyfd, ttyfd, buf, NULL, NULL);
if (i == -1) {
error("openpty: %.100s", strerror(errno));
return 0;
}
strlcpy(namebuf, buf, namebuflen); /* possible truncation */
return 1;
}
/* Releases the tty. Its ownership is returned to root, and permissions to 0666. */
void
pty_release(const char *tty)
{
if (chown(tty, (uid_t) 0, (gid_t) 0) == -1)
error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
if (chmod(tty, (mode_t) 0666) == -1)
error("chmod %.100s 0666 failed: %.100s", tty, strerror(errno));
}
/* Makes the tty the process's controlling tty and sets it to sane modes. */
void
pty_make_controlling_tty(int *ttyfd, const char *tty)
{
int fd;
/* First disconnect from the old controlling tty. */
#ifdef TIOCNOTTY
fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
if (fd >= 0) {
(void) ioctl(fd, TIOCNOTTY, NULL);
close(fd);
}
#endif /* TIOCNOTTY */
if (setsid() == -1)
error("setsid: %.100s", strerror(errno));
/*
* Verify that we are successfully disconnected from the controlling
* tty.
*/
fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
if (fd >= 0) {
error("Failed to disconnect from controlling tty.");
close(fd);
}
/* Make it our controlling tty. */
#ifdef TIOCSCTTY
debug("Setting controlling tty using TIOCSCTTY.");
if (ioctl(*ttyfd, TIOCSCTTY, NULL) == -1)
error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
#endif /* TIOCSCTTY */
fd = open(tty, O_RDWR);
if (fd == -1)
error("%.100s: %.100s", tty, strerror(errno));
else
close(fd);
/* Verify that we now have a controlling tty. */
fd = open(_PATH_TTY, O_WRONLY);
if (fd == -1)
error("open /dev/tty failed - could not set controlling tty: %.100s",
strerror(errno));
else
close(fd);
}
/* Changes the window size associated with the pty. */
void
pty_change_window_size(int ptyfd, u_int row, u_int col,
u_int xpixel, u_int ypixel)
{
struct winsize w;
/* may truncate u_int -> u_short */
w.ws_row = row;
w.ws_col = col;
w.ws_xpixel = xpixel;
w.ws_ypixel = ypixel;
(void) ioctl(ptyfd, TIOCSWINSZ, &w);
}
void
pty_setowner(struct passwd *pw, const char *tty)
{
struct group *grp;
gid_t gid;
mode_t mode;
struct stat st;
/* Determine the group to make the owner of the tty. */
grp = getgrnam("tty");
if (grp == NULL)
fatal("no tty group");
gid = (grp != NULL) ? grp->gr_gid : pw->pw_gid;
mode = (grp != NULL) ? 0620 : 0600;
/*
* Change owner and mode of the tty as required.
* Warn but continue if filesystem is read-only and the uids match/
* tty is owned by root.
*/
if (stat(tty, &st) == -1)
fatal("stat(%.100s) failed: %.100s", tty,
strerror(errno));
if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
if (chown(tty, pw->pw_uid, gid) == -1) {
if (errno == EROFS &&
(st.st_uid == pw->pw_uid || st.st_uid == 0))
debug("chown(%.100s, %u, %u) failed: %.100s",
tty, (u_int)pw->pw_uid, (u_int)gid,
strerror(errno));
else
fatal("chown(%.100s, %u, %u) failed: %.100s",
tty, (u_int)pw->pw_uid, (u_int)gid,
strerror(errno));
}
}
if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
if (chmod(tty, mode) == -1) {
if (errno == EROFS &&
(st.st_mode & (S_IRGRP | S_IROTH)) == 0)
debug("chmod(%.100s, 0%o) failed: %.100s",
tty, (u_int)mode, strerror(errno));
else
fatal("chmod(%.100s, 0%o) failed: %.100s",
tty, (u_int)mode, strerror(errno));
}
}
}
/* Disconnect from the controlling tty. */
void
disconnect_controlling_tty(void)
{
int fd;
if ((fd = open(_PATH_TTY, O_RDWR | O_NOCTTY)) >= 0) {
(void) ioctl(fd, TIOCNOTTY, NULL);
close(fd);
}
}
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