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 <stdio.h>
31 #include <string.h>
32 #include <termios.h>
33 #ifdef HAVE_UTIL_H
34 # include <util.h>
35 #endif
36 #include <unistd.h>
37
38 #include "sshpty.h"
39 #include "log.h"
40 #include "misc.h"
41
42 #ifdef HAVE_PTY_H
43 # include <pty.h>
44 #endif
45
46 #ifndef O_NOCTTY
47 #define O_NOCTTY 0
48 #endif
49
50 #ifdef __APPLE__
51 # include <AvailabilityMacros.h>
52 # if (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_5)
53 # define __APPLE_PRIVPTY__
54 # endif
55 #endif
56
57 /*
58 * Allocates and opens a pty. Returns 0 if no pty could be allocated, or
59 * nonzero if a pty was successfully allocated. On success, open file
60 * descriptors for the pty and tty sides and the name of the tty side are
61 * returned (the buffer must be able to hold at least 64 characters).
62 */
63
64 int
pty_allocate(int * ptyfd,int * ttyfd,char * namebuf,size_t namebuflen)65 pty_allocate(int *ptyfd, int *ttyfd, char *namebuf, size_t namebuflen)
66 {
67 /* openpty(3) exists in OSF/1 and some other os'es */
68 char *name;
69 int i;
70
71 i = openpty(ptyfd, ttyfd, NULL, NULL, NULL);
72 if (i == -1) {
73 error("openpty: %.100s", strerror(errno));
74 return 0;
75 }
76 name = ttyname(*ttyfd);
77 if (!name)
78 fatal("openpty returns device for which ttyname fails.");
79
80 strlcpy(namebuf, name, namebuflen); /* possible truncation */
81 return 1;
82 }
83
84 /* Releases the tty. Its ownership is returned to root, and permissions to 0666. */
85
86 void
pty_release(const char * tty)87 pty_release(const char *tty)
88 {
89 #if !defined(__APPLE_PRIVPTY__) && !defined(HAVE_OPENPTY)
90 if (chown(tty, (uid_t) 0, (gid_t) 0) == -1)
91 error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
92 if (chmod(tty, (mode_t) 0666) == -1)
93 error("chmod %.100s 0666 failed: %.100s", tty, strerror(errno));
94 #endif /* !__APPLE_PRIVPTY__ && !HAVE_OPENPTY */
95 }
96
97 /* Makes the tty the process's controlling tty and sets it to sane modes. */
98
99 void
pty_make_controlling_tty(int * ttyfd,const char * tty)100 pty_make_controlling_tty(int *ttyfd, const char *tty)
101 {
102 int fd;
103
104 /* First disconnect from the old controlling tty. */
105 #ifdef TIOCNOTTY
106 fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
107 if (fd >= 0) {
108 (void) ioctl(fd, TIOCNOTTY, NULL);
109 close(fd);
110 }
111 #endif /* TIOCNOTTY */
112 if (setsid() == -1)
113 error("setsid: %.100s", strerror(errno));
114
115 /*
116 * Verify that we are successfully disconnected from the controlling
117 * tty.
118 */
119 fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
120 if (fd >= 0) {
121 error("Failed to disconnect from controlling tty.");
122 close(fd);
123 }
124 /* Make it our controlling tty. */
125 #ifdef TIOCSCTTY
126 debug("Setting controlling tty using TIOCSCTTY.");
127 if (ioctl(*ttyfd, TIOCSCTTY, NULL) < 0)
128 error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
129 #endif /* TIOCSCTTY */
130 #ifdef NEED_SETPGRP
131 if (setpgrp(0,0) < 0)
132 error("SETPGRP %s",strerror(errno));
133 #endif /* NEED_SETPGRP */
134 fd = open(tty, O_RDWR);
135 if (fd == -1)
136 error("%.100s: %.100s", tty, strerror(errno));
137 else
138 close(fd);
139
140 /* Verify that we now have a controlling tty. */
141 fd = open(_PATH_TTY, O_WRONLY);
142 if (fd == -1)
143 error("open /dev/tty failed - could not set controlling tty: %.100s",
144 strerror(errno));
145 else
146 close(fd);
147 }
148
149 /* Changes the window size associated with the pty. */
150
151 void
pty_change_window_size(int ptyfd,u_int row,u_int col,u_int xpixel,u_int ypixel)152 pty_change_window_size(int ptyfd, u_int row, u_int col,
153 u_int xpixel, u_int ypixel)
154 {
155 struct winsize w;
156
157 /* may truncate u_int -> u_short */
158 w.ws_row = row;
159 w.ws_col = col;
160 w.ws_xpixel = xpixel;
161 w.ws_ypixel = ypixel;
162 (void) ioctl(ptyfd, TIOCSWINSZ, &w);
163 }
164
165 void
pty_setowner(struct passwd * pw,const char * tty)166 pty_setowner(struct passwd *pw, const char *tty)
167 {
168 struct group *grp;
169 gid_t gid;
170 mode_t mode;
171 struct stat st;
172
173 /* Determine the group to make the owner of the tty. */
174 grp = getgrnam("tty");
175 if (grp == NULL)
176 debug("%s: no tty group", __func__);
177 gid = (grp != NULL) ? grp->gr_gid : pw->pw_gid;
178 mode = (grp != NULL) ? 0620 : 0600;
179
180 /*
181 * Change owner and mode of the tty as required.
182 * Warn but continue if filesystem is read-only and the uids match/
183 * tty is owned by root.
184 */
185 if (stat(tty, &st) == -1)
186 fatal("stat(%.100s) failed: %.100s", tty,
187 strerror(errno));
188
189 #ifdef WITH_SELINUX
190 ssh_selinux_setup_pty(pw->pw_name, tty);
191 #endif
192
193 if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
194 if (chown(tty, pw->pw_uid, gid) == -1) {
195 if (errno == EROFS &&
196 (st.st_uid == pw->pw_uid || st.st_uid == 0))
197 debug("chown(%.100s, %u, %u) failed: %.100s",
198 tty, (u_int)pw->pw_uid, (u_int)gid,
199 strerror(errno));
200 else
201 fatal("chown(%.100s, %u, %u) failed: %.100s",
202 tty, (u_int)pw->pw_uid, (u_int)gid,
203 strerror(errno));
204 }
205 }
206
207 if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
208 if (chmod(tty, mode) == -1) {
209 if (errno == EROFS &&
210 (st.st_mode & (S_IRGRP | S_IROTH)) == 0)
211 debug("chmod(%.100s, 0%o) failed: %.100s",
212 tty, (u_int)mode, strerror(errno));
213 else
214 fatal("chmod(%.100s, 0%o) failed: %.100s",
215 tty, (u_int)mode, strerror(errno));
216 }
217 }
218 }
219
220 /* Disconnect from the controlling tty. */
221 void
disconnect_controlling_tty(void)222 disconnect_controlling_tty(void)
223 {
224 #ifdef TIOCNOTTY
225 int fd;
226
227 if ((fd = open(_PATH_TTY, O_RDWR | O_NOCTTY)) >= 0) {
228 (void) ioctl(fd, TIOCNOTTY, NULL);
229 close(fd);
230 }
231 #endif /* TIOCNOTTY */
232 }
233