xref: /openssh-portable/sshpty.c (revision c5cfa90e)
1 /* $OpenBSD: sshpty.c,v 1.34 2019/07/04 16:20:10 deraadt 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 
63 int
pty_allocate(int * ptyfd,int * ttyfd,char * namebuf,size_t namebuflen)64 pty_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 == -1) {
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 
85 void
pty_release(const char * tty)86 pty_release(const char *tty)
87 {
88 #if !defined(__APPLE_PRIVPTY__) && !defined(HAVE_OPENPTY)
89 	if (chown(tty, (uid_t) 0, (gid_t) 0) == -1)
90 		error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
91 	if (chmod(tty, (mode_t) 0666) == -1)
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 
98 void
pty_make_controlling_tty(int * ttyfd,const char * tty)99 pty_make_controlling_tty(int *ttyfd, const char *tty)
100 {
101 	int fd;
102 
103 	/* First disconnect from the old controlling tty. */
104 #ifdef TIOCNOTTY
105 	fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
106 	if (fd >= 0) {
107 		(void) ioctl(fd, TIOCNOTTY, NULL);
108 		close(fd);
109 	}
110 #endif /* TIOCNOTTY */
111 	if (setsid() == -1)
112 		error("setsid: %.100s", strerror(errno));
113 
114 	/*
115 	 * Verify that we are successfully disconnected from the controlling
116 	 * tty.
117 	 */
118 	fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
119 	if (fd >= 0) {
120 		error("Failed to disconnect from controlling tty.");
121 		close(fd);
122 	}
123 	/* Make it our controlling tty. */
124 #ifdef TIOCSCTTY
125 	debug("Setting controlling tty using TIOCSCTTY.");
126 	if (ioctl(*ttyfd, TIOCSCTTY, NULL) < 0)
127 		error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
128 #endif /* TIOCSCTTY */
129 #ifdef NEED_SETPGRP
130 	if (setpgrp(0,0) < 0)
131 		error("SETPGRP %s",strerror(errno));
132 #endif /* NEED_SETPGRP */
133 	fd = open(tty, O_RDWR);
134 	if (fd == -1)
135 		error("%.100s: %.100s", tty, strerror(errno));
136 	else
137 		close(fd);
138 
139 	/* Verify that we now have a controlling tty. */
140 	fd = open(_PATH_TTY, O_WRONLY);
141 	if (fd == -1)
142 		error("open /dev/tty failed - could not set controlling tty: %.100s",
143 		    strerror(errno));
144 	else
145 		close(fd);
146 }
147 
148 /* Changes the window size associated with the pty. */
149 
150 void
pty_change_window_size(int ptyfd,u_int row,u_int col,u_int xpixel,u_int ypixel)151 pty_change_window_size(int ptyfd, u_int row, u_int col,
152 	u_int xpixel, u_int ypixel)
153 {
154 	struct winsize w;
155 
156 	/* may truncate u_int -> u_short */
157 	w.ws_row = row;
158 	w.ws_col = col;
159 	w.ws_xpixel = xpixel;
160 	w.ws_ypixel = ypixel;
161 	(void) ioctl(ptyfd, TIOCSWINSZ, &w);
162 }
163 
164 void
pty_setowner(struct passwd * pw,const char * tty)165 pty_setowner(struct passwd *pw, const char *tty)
166 {
167 	struct group *grp;
168 	gid_t gid;
169 	mode_t mode;
170 	struct stat st;
171 
172 	/* Determine the group to make the owner of the tty. */
173 	grp = getgrnam("tty");
174 	if (grp == NULL)
175 		debug("%s: no tty group", __func__);
176 	gid = (grp != NULL) ? grp->gr_gid : pw->pw_gid;
177 	mode = (grp != NULL) ? 0620 : 0600;
178 
179 	/*
180 	 * Change owner and mode of the tty as required.
181 	 * Warn but continue if filesystem is read-only and the uids match/
182 	 * tty is owned by root.
183 	 */
184 	if (stat(tty, &st) == -1)
185 		fatal("stat(%.100s) failed: %.100s", tty,
186 		    strerror(errno));
187 
188 #ifdef WITH_SELINUX
189 	ssh_selinux_setup_pty(pw->pw_name, tty);
190 #endif
191 
192 	if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
193 		if (chown(tty, pw->pw_uid, gid) == -1) {
194 			if (errno == EROFS &&
195 			    (st.st_uid == pw->pw_uid || st.st_uid == 0))
196 				debug("chown(%.100s, %u, %u) failed: %.100s",
197 				    tty, (u_int)pw->pw_uid, (u_int)gid,
198 				    strerror(errno));
199 			else
200 				fatal("chown(%.100s, %u, %u) failed: %.100s",
201 				    tty, (u_int)pw->pw_uid, (u_int)gid,
202 				    strerror(errno));
203 		}
204 	}
205 
206 	if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
207 		if (chmod(tty, mode) == -1) {
208 			if (errno == EROFS &&
209 			    (st.st_mode & (S_IRGRP | S_IROTH)) == 0)
210 				debug("chmod(%.100s, 0%o) failed: %.100s",
211 				    tty, (u_int)mode, strerror(errno));
212 			else
213 				fatal("chmod(%.100s, 0%o) failed: %.100s",
214 				    tty, (u_int)mode, strerror(errno));
215 		}
216 	}
217 }
218 
219 /* Disconnect from the controlling tty. */
220 void
disconnect_controlling_tty(void)221 disconnect_controlling_tty(void)
222 {
223 #ifdef TIOCNOTTY
224 	int fd;
225 
226 	if ((fd = open(_PATH_TTY, O_RDWR | O_NOCTTY)) >= 0) {
227 		(void) ioctl(fd, TIOCNOTTY, NULL);
228 		close(fd);
229 	}
230 #endif /* TIOCNOTTY */
231 }
232