sshpty.c revision 181111 
1/* $OpenBSD: sshpty.c,v 1.28 2007/09/11 23:49:09 stevesk 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/*
50 * Allocates and opens a pty.  Returns 0 if no pty could be allocated, or
51 * nonzero if a pty was successfully allocated.  On success, open file
52 * descriptors for the pty and tty sides and the name of the tty side are
53 * returned (the buffer must be able to hold at least 64 characters).
54 */
55
56int
57pty_allocate(int *ptyfd, int *ttyfd, char *namebuf, size_t namebuflen)
58{
59	/* openpty(3) exists in OSF/1 and some other os'es */
60	char *name;
61	int i;
62
63	i = openpty(ptyfd, ttyfd, NULL, NULL, NULL);
64	if (i < 0) {
65		error("openpty: %.100s", strerror(errno));
66		return 0;
67	}
68	name = ttyname(*ttyfd);
69	if (!name)
70		fatal("openpty returns device for which ttyname fails.");
71
72	strlcpy(namebuf, name, namebuflen);	/* possible truncation */
73	return 1;
74}
75
76/* Releases the tty.  Its ownership is returned to root, and permissions to 0666. */
77
78void
79pty_release(const char *tty)
80{
81	if (chown(tty, (uid_t) 0, (gid_t) 0) < 0)
82		error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
83	if (chmod(tty, (mode_t) 0666) < 0)
84		error("chmod %.100s 0666 failed: %.100s", tty, strerror(errno));
85}
86
87/* Makes the tty the process's controlling tty and sets it to sane modes. */
88
89void
90pty_make_controlling_tty(int *ttyfd, const char *tty)
91{
92	int fd;
93#ifdef USE_VHANGUP
94	void *old;
95#endif /* USE_VHANGUP */
96
97#ifdef _UNICOS
98	if (setsid() < 0)
99		error("setsid: %.100s", strerror(errno));
100
101	fd = open(tty, O_RDWR|O_NOCTTY);
102	if (fd != -1) {
103		signal(SIGHUP, SIG_IGN);
104		ioctl(fd, TCVHUP, (char *)NULL);
105		signal(SIGHUP, SIG_DFL);
106		setpgid(0, 0);
107		close(fd);
108	} else {
109		error("Failed to disconnect from controlling tty.");
110	}
111
112	debug("Setting controlling tty using TCSETCTTY.");
113	ioctl(*ttyfd, TCSETCTTY, NULL);
114	fd = open("/dev/tty", O_RDWR);
115	if (fd < 0)
116		error("%.100s: %.100s", tty, strerror(errno));
117	close(*ttyfd);
118	*ttyfd = fd;
119#else /* _UNICOS */
120
121	/* First disconnect from the old controlling tty. */
122#ifdef TIOCNOTTY
123	fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
124	if (fd >= 0) {
125		(void) ioctl(fd, TIOCNOTTY, NULL);
126		close(fd);
127	}
128#endif /* TIOCNOTTY */
129	if (setsid() < 0)
130		error("setsid: %.100s", strerror(errno));
131
132	/*
133	 * Verify that we are successfully disconnected from the controlling
134	 * tty.
135	 */
136	fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
137	if (fd >= 0) {
138		error("Failed to disconnect from controlling tty.");
139		close(fd);
140	}
141	/* Make it our controlling tty. */
142#ifdef TIOCSCTTY
143	debug("Setting controlling tty using TIOCSCTTY.");
144	if (ioctl(*ttyfd, TIOCSCTTY, NULL) < 0)
145		error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
146#endif /* TIOCSCTTY */
147#ifdef NEED_SETPGRP
148	if (setpgrp(0,0) < 0)
149		error("SETPGRP %s",strerror(errno));
150#endif /* NEED_SETPGRP */
151#ifdef USE_VHANGUP
152	old = signal(SIGHUP, SIG_IGN);
153	vhangup();
154	signal(SIGHUP, old);
155#endif /* USE_VHANGUP */
156	fd = open(tty, O_RDWR);
157	if (fd < 0) {
158		error("%.100s: %.100s", tty, strerror(errno));
159	} else {
160#ifdef USE_VHANGUP
161		close(*ttyfd);
162		*ttyfd = fd;
163#else /* USE_VHANGUP */
164		close(fd);
165#endif /* USE_VHANGUP */
166	}
167	/* Verify that we now have a controlling tty. */
168	fd = open(_PATH_TTY, O_WRONLY);
169	if (fd < 0)
170		error("open /dev/tty failed - could not set controlling tty: %.100s",
171		    strerror(errno));
172	else
173		close(fd);
174#endif /* _UNICOS */
175}
176
177/* Changes the window size associated with the pty. */
178
179void
180pty_change_window_size(int ptyfd, u_int row, u_int col,
181	u_int xpixel, u_int ypixel)
182{
183	struct winsize w;
184
185	/* may truncate u_int -> u_short */
186	w.ws_row = row;
187	w.ws_col = col;
188	w.ws_xpixel = xpixel;
189	w.ws_ypixel = ypixel;
190	(void) ioctl(ptyfd, TIOCSWINSZ, &w);
191}
192
193void
194pty_setowner(struct passwd *pw, const char *tty)
195{
196	struct group *grp;
197	gid_t gid;
198	mode_t mode;
199	struct stat st;
200
201	/* Determine the group to make the owner of the tty. */
202	grp = getgrnam("tty");
203	if (grp) {
204		gid = grp->gr_gid;
205		mode = S_IRUSR | S_IWUSR | S_IWGRP;
206	} else {
207		gid = pw->pw_gid;
208		mode = S_IRUSR | S_IWUSR | S_IWGRP | S_IWOTH;
209	}
210
211	/*
212	 * Change owner and mode of the tty as required.
213	 * Warn but continue if filesystem is read-only and the uids match/
214	 * tty is owned by root.
215	 */
216	if (stat(tty, &st))
217		fatal("stat(%.100s) failed: %.100s", tty,
218		    strerror(errno));
219
220#ifdef WITH_SELINUX
221	ssh_selinux_setup_pty(pw->pw_name, tty);
222#endif
223
224	if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
225		if (chown(tty, pw->pw_uid, gid) < 0) {
226			if (errno == EROFS &&
227			    (st.st_uid == pw->pw_uid || st.st_uid == 0))
228				debug("chown(%.100s, %u, %u) failed: %.100s",
229				    tty, (u_int)pw->pw_uid, (u_int)gid,
230				    strerror(errno));
231			else
232				fatal("chown(%.100s, %u, %u) failed: %.100s",
233				    tty, (u_int)pw->pw_uid, (u_int)gid,
234				    strerror(errno));
235		}
236	}
237
238	if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
239		if (chmod(tty, mode) < 0) {
240			if (errno == EROFS &&
241			    (st.st_mode & (S_IRGRP | S_IROTH)) == 0)
242				debug("chmod(%.100s, 0%o) failed: %.100s",
243				    tty, (u_int)mode, strerror(errno));
244			else
245				fatal("chmod(%.100s, 0%o) failed: %.100s",
246				    tty, (u_int)mode, strerror(errno));
247		}
248	}
249}
250