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