1 /* $NetBSD: sshpty.c,v 1.8 2019/10/12 18:32:22 christos Exp $ */
2 /* $OpenBSD: sshpty.c,v 1.34 2019/07/04 16:20:10 deraadt Exp $ */
3 /*
4 * Author: Tatu Ylonen <ylo@cs.hut.fi>
5 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
6 * All rights reserved
7 * Allocating a pseudo-terminal, and making it the controlling tty.
8 *
9 * As far as I am concerned, the code I have written for this software
10 * can be used freely for any purpose. Any derived versions of this
11 * software must be clearly marked as such, and if the derived work is
12 * incompatible with the protocol description in the RFC file, it must be
13 * called by a name other than "ssh" or "Secure Shell".
14 */
15
16 #include "includes.h"
17 __RCSID("$NetBSD: sshpty.c,v 1.8 2019/10/12 18:32:22 christos Exp $");
18 #include <sys/types.h>
19 #include <sys/ioctl.h>
20 #include <sys/stat.h>
21
22 #include <errno.h>
23 #include <fcntl.h>
24 #include <grp.h>
25 #include <paths.h>
26 #include <pwd.h>
27 #include <stdarg.h>
28 #include <string.h>
29 #include <termios.h>
30 #include <unistd.h>
31 #include <util.h>
32
33 #include "sshpty.h"
34 #include "log.h"
35
36 #ifndef O_NOCTTY
37 #define O_NOCTTY 0
38 #endif
39
40 /*
41 * Allocates and opens a pty. Returns 0 if no pty could be allocated, or
42 * nonzero if a pty was successfully allocated. On success, open file
43 * descriptors for the pty and tty sides and the name of the tty side are
44 * returned (the buffer must be able to hold at least 64 characters).
45 */
46
47 int
pty_allocate(int * ptyfd,int * ttyfd,char * namebuf,size_t namebuflen)48 pty_allocate(int *ptyfd, int *ttyfd, char *namebuf, size_t namebuflen)
49 {
50 char buf[64];
51 int i;
52
53 i = openpty(ptyfd, ttyfd, buf, NULL, NULL);
54 if (i == -1) {
55 error("openpty: %.100s", strerror(errno));
56 return 0;
57 }
58 strlcpy(namebuf, buf, namebuflen); /* possible truncation */
59 return 1;
60 }
61
62 /* Releases the tty. Its ownership is returned to root, and permissions to 0666. */
63
64 void
pty_release(const char * tty)65 pty_release(const char *tty)
66 {
67 if (chown(tty, (uid_t) 0, (gid_t) 0) == -1)
68 error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
69 if (chmod(tty, (mode_t) 0666) == -1)
70 error("chmod %.100s 0666 failed: %.100s", tty, strerror(errno));
71 }
72
73 /* Makes the tty the process's controlling tty and sets it to sane modes. */
74
75 void
pty_make_controlling_tty(int * ttyfd,const char * tty)76 pty_make_controlling_tty(int *ttyfd, const char *tty)
77 {
78 int fd;
79
80 /* First disconnect from the old controlling tty. */
81 #ifdef TIOCNOTTY
82 fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
83 if (fd >= 0) {
84 (void) ioctl(fd, TIOCNOTTY, NULL);
85 close(fd);
86 }
87 #endif /* TIOCNOTTY */
88 if (setsid() == -1)
89 error("setsid: %.100s", strerror(errno));
90
91 /*
92 * Verify that we are successfully disconnected from the controlling
93 * tty.
94 */
95 fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
96 if (fd >= 0) {
97 error("Failed to disconnect from controlling tty.");
98 close(fd);
99 }
100 /* Make it our controlling tty. */
101 #ifdef TIOCSCTTY
102 debug("Setting controlling tty using TIOCSCTTY.");
103 if (ioctl(*ttyfd, TIOCSCTTY, NULL) == -1)
104 error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
105 #endif /* TIOCSCTTY */
106 fd = open(tty, O_RDWR);
107 if (fd == -1)
108 error("%.100s: %.100s", tty, strerror(errno));
109 else
110 close(fd);
111
112 /* Verify that we now have a controlling tty. */
113 fd = open(_PATH_TTY, O_WRONLY);
114 if (fd == -1)
115 error("open /dev/tty failed - could not set controlling tty: %.100s",
116 strerror(errno));
117 else
118 close(fd);
119 }
120
121 /* Changes the window size associated with the pty. */
122
123 void
pty_change_window_size(int ptyfd,u_int row,u_int col,u_int xpixel,u_int ypixel)124 pty_change_window_size(int ptyfd, u_int row, u_int col,
125 u_int xpixel, u_int ypixel)
126 {
127 struct winsize w;
128
129 /* may truncate u_int -> u_short */
130 w.ws_row = row;
131 w.ws_col = col;
132 w.ws_xpixel = xpixel;
133 w.ws_ypixel = ypixel;
134 (void) ioctl(ptyfd, TIOCSWINSZ, &w);
135 }
136
137 void
pty_setowner(struct passwd * pw,const char * tty)138 pty_setowner(struct passwd *pw, const char *tty)
139 {
140 struct group *grp;
141 gid_t gid;
142 mode_t mode;
143 struct stat st;
144
145 /* Determine the group to make the owner of the tty. */
146 grp = getgrnam("tty");
147 if (grp == NULL)
148 fatal("no tty group");
149 gid = (grp != NULL) ? grp->gr_gid : pw->pw_gid;
150 mode = (grp != NULL) ? 0620 : 0600;
151
152 /*
153 * Change owner and mode of the tty as required.
154 * Warn but continue if filesystem is read-only and the uids match/
155 * tty is owned by root.
156 */
157 if (stat(tty, &st) == -1)
158 fatal("stat(%.100s) failed: %.100s", tty,
159 strerror(errno));
160
161 if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
162 if (chown(tty, pw->pw_uid, gid) == -1) {
163 if (errno == EROFS &&
164 (st.st_uid == pw->pw_uid || st.st_uid == 0))
165 debug("chown(%.100s, %u, %u) failed: %.100s",
166 tty, (u_int)pw->pw_uid, (u_int)gid,
167 strerror(errno));
168 else
169 fatal("chown(%.100s, %u, %u) failed: %.100s",
170 tty, (u_int)pw->pw_uid, (u_int)gid,
171 strerror(errno));
172 }
173 }
174
175 if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
176 if (chmod(tty, mode) == -1) {
177 if (errno == EROFS &&
178 (st.st_mode & (S_IRGRP | S_IROTH)) == 0)
179 debug("chmod(%.100s, 0%o) failed: %.100s",
180 tty, (u_int)mode, strerror(errno));
181 else
182 fatal("chmod(%.100s, 0%o) failed: %.100s",
183 tty, (u_int)mode, strerror(errno));
184 }
185 }
186 }
187
188 /* Disconnect from the controlling tty. */
189 void
disconnect_controlling_tty(void)190 disconnect_controlling_tty(void)
191 {
192 int fd;
193
194 if ((fd = open(_PATH_TTY, O_RDWR | O_NOCTTY)) >= 0) {
195 (void) ioctl(fd, TIOCNOTTY, NULL);
196 close(fd);
197 }
198 }
199