sshpty.c revision 323134 
1/* $OpenBSD: sshpty.c,v 1.31 2016/11/29 03:54:50 dtucker Exp $ */
2/*
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 *                    All rights reserved
6 * Allocating a pseudo-terminal, and making it the controlling tty.
7 *
8 * As far as I am concerned, the code I have written for this software
9 * can be used freely for any purpose.  Any derived versions of this
10 * software must be clearly marked as such, and if the derived work is
11 * incompatible with the protocol description in the RFC file, it must be
12 * called by a name other than "ssh" or "Secure Shell".
13 */
14
15#include "includes.h"
16
17#include <sys/types.h>
18#include <sys/ioctl.h>
19#include <sys/stat.h>
20#include <signal.h>
21
22#include <errno.h>
23#include <fcntl.h>
24#include <grp.h>
25#ifdef HAVE_PATHS_H
26# include <paths.h>
27#endif
28#include <pwd.h>
29#include <stdarg.h>
30#include <string.h>
31#include <termios.h>
32#ifdef HAVE_UTIL_H
33# include <util.h>
34#endif
35#include <unistd.h>
36
37#include "sshpty.h"
38#include "log.h"
39#include "misc.h"
40
41#ifdef HAVE_PTY_H
42# include <pty.h>
43#endif
44
45#ifndef O_NOCTTY
46#define O_NOCTTY 0
47#endif
48
49#ifdef __APPLE__
50# include <AvailabilityMacros.h>
51# if (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_5)
52#  define __APPLE_PRIVPTY__
53# endif
54#endif
55
56/*
57 * Allocates and opens a pty.  Returns 0 if no pty could be allocated, or
58 * nonzero if a pty was successfully allocated.  On success, open file
59 * descriptors for the pty and tty sides and the name of the tty side are
60 * returned (the buffer must be able to hold at least 64 characters).
61 */
62
63int
64pty_allocate(int *ptyfd, int *ttyfd, char *namebuf, size_t namebuflen)
65{
66	/* openpty(3) exists in OSF/1 and some other os'es */
67	char *name;
68	int i;
69
70	i = openpty(ptyfd, ttyfd, NULL, NULL, NULL);
71	if (i < 0) {
72		error("openpty: %.100s", strerror(errno));
73		return 0;
74	}
75	name = ttyname(*ttyfd);
76	if (!name)
77		fatal("openpty returns device for which ttyname fails.");
78
79	strlcpy(namebuf, name, namebuflen);	/* possible truncation */
80	return 1;
81}
82
83/* Releases the tty.  Its ownership is returned to root, and permissions to 0666. */
84
85void
86pty_release(const char *tty)
87{
88#if !defined(__APPLE_PRIVPTY__) && !defined(HAVE_OPENPTY)
89	if (chown(tty, (uid_t) 0, (gid_t) 0) < 0)
90		error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
91	if (chmod(tty, (mode_t) 0666) < 0)
92		error("chmod %.100s 0666 failed: %.100s", tty, strerror(errno));
93#endif /* !__APPLE_PRIVPTY__ && !HAVE_OPENPTY */
94}
95
96/* Makes the tty the process's controlling tty and sets it to sane modes. */
97
98void
99pty_make_controlling_tty(int *ttyfd, const char *tty)
100{
101	int fd;
102
103#ifdef _UNICOS
104	if (setsid() < 0)
105		error("setsid: %.100s", strerror(errno));
106
107	fd = open(tty, O_RDWR|O_NOCTTY);
108	if (fd != -1) {
109		signal(SIGHUP, SIG_IGN);
110		ioctl(fd, TCVHUP, (char *)NULL);
111		signal(SIGHUP, SIG_DFL);
112		setpgid(0, 0);
113		close(fd);
114	} else {
115		error("Failed to disconnect from controlling tty.");
116	}
117
118	debug("Setting controlling tty using TCSETCTTY.");
119	ioctl(*ttyfd, TCSETCTTY, NULL);
120	fd = open("/dev/tty", O_RDWR);
121	if (fd < 0)
122		error("%.100s: %.100s", tty, strerror(errno));
123	close(*ttyfd);
124	*ttyfd = fd;
125#else /* _UNICOS */
126
127	/* First disconnect from the old controlling tty. */
128#ifdef TIOCNOTTY
129	fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
130	if (fd >= 0) {
131		(void) ioctl(fd, TIOCNOTTY, NULL);
132		close(fd);
133	}
134#endif /* TIOCNOTTY */
135	if (setsid() < 0)
136		error("setsid: %.100s", strerror(errno));
137
138	/*
139	 * Verify that we are successfully disconnected from the controlling
140	 * tty.
141	 */
142	fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
143	if (fd >= 0) {
144		error("Failed to disconnect from controlling tty.");
145		close(fd);
146	}
147	/* Make it our controlling tty. */
148#ifdef TIOCSCTTY
149	debug("Setting controlling tty using TIOCSCTTY.");
150	if (ioctl(*ttyfd, TIOCSCTTY, NULL) < 0)
151		error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
152#endif /* TIOCSCTTY */
153#ifdef NEED_SETPGRP
154	if (setpgrp(0,0) < 0)
155		error("SETPGRP %s",strerror(errno));
156#endif /* NEED_SETPGRP */
157	fd = open(tty, O_RDWR);
158	if (fd < 0)
159		error("%.100s: %.100s", tty, strerror(errno));
160	else
161		close(fd);
162
163	/* Verify that we now have a controlling tty. */
164	fd = open(_PATH_TTY, O_WRONLY);
165	if (fd < 0)
166		error("open /dev/tty failed - could not set controlling tty: %.100s",
167		    strerror(errno));
168	else
169		close(fd);
170#endif /* _UNICOS */
171}
172
173/* Changes the window size associated with the pty. */
174
175void
176pty_change_window_size(int ptyfd, u_int row, u_int col,
177	u_int xpixel, u_int ypixel)
178{
179	struct winsize w;
180
181	/* may truncate u_int -> u_short */
182	w.ws_row = row;
183	w.ws_col = col;
184	w.ws_xpixel = xpixel;
185	w.ws_ypixel = ypixel;
186	(void) ioctl(ptyfd, TIOCSWINSZ, &w);
187}
188
189void
190pty_setowner(struct passwd *pw, const char *tty)
191{
192	struct group *grp;
193	gid_t gid;
194	mode_t mode;
195	struct stat st;
196
197	/* Determine the group to make the owner of the tty. */
198	grp = getgrnam("tty");
199	gid = (grp != NULL) ? grp->gr_gid : pw->pw_gid;
200	mode = (grp != NULL) ? 0620 : 0600;
201
202	/*
203	 * Change owner and mode of the tty as required.
204	 * Warn but continue if filesystem is read-only and the uids match/
205	 * tty is owned by root.
206	 */
207	if (stat(tty, &st))
208		fatal("stat(%.100s) failed: %.100s", tty,
209		    strerror(errno));
210
211#ifdef WITH_SELINUX
212	ssh_selinux_setup_pty(pw->pw_name, tty);
213#endif
214
215	if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
216		if (chown(tty, pw->pw_uid, gid) < 0) {
217			if (errno == EROFS &&
218			    (st.st_uid == pw->pw_uid || st.st_uid == 0))
219				debug("chown(%.100s, %u, %u) failed: %.100s",
220				    tty, (u_int)pw->pw_uid, (u_int)gid,
221				    strerror(errno));
222			else
223				fatal("chown(%.100s, %u, %u) failed: %.100s",
224				    tty, (u_int)pw->pw_uid, (u_int)gid,
225				    strerror(errno));
226		}
227	}
228
229	if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
230		if (chmod(tty, mode) < 0) {
231			if (errno == EROFS &&
232			    (st.st_mode & (S_IRGRP | S_IROTH)) == 0)
233				debug("chmod(%.100s, 0%o) failed: %.100s",
234				    tty, (u_int)mode, strerror(errno));
235			else
236				fatal("chmod(%.100s, 0%o) failed: %.100s",
237				    tty, (u_int)mode, strerror(errno));
238		}
239	}
240}
241
242/* Disconnect from the controlling tty. */
243void
244disconnect_controlling_tty(void)
245{
246#ifdef TIOCNOTTY
247	int fd;
248
249	if ((fd = open(_PATH_TTY, O_RDWR | O_NOCTTY)) >= 0) {
250		(void) ioctl(fd, TIOCNOTTY, NULL);
251		close(fd);
252	}
253#endif /* TIOCNOTTY */
254}
255