jcs.org
jcs's openbsd hax
openbsd
1/* $OpenBSD: sshpty.c,v 1.35 2026/02/11 17:05:32 dtucker 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 <sys/types.h>
16#include <sys/ioctl.h>
17#include <sys/stat.h>
18
19#include <errno.h>
20#include <fcntl.h>
21#include <grp.h>
22#include <paths.h>
23#include <pwd.h>
24#include <signal.h>
25#include <stdarg.h>
26#include <stdio.h>
27#include <string.h>
28#include <termios.h>
29#include <unistd.h>
30#include <util.h>
31
32#include "sshpty.h"
33#include "log.h"
34
35#ifndef O_NOCTTY
36#define O_NOCTTY 0
37#endif
38
39/*
40 * Allocates and opens a pty. Returns 0 if no pty could be allocated, or
41 * nonzero if a pty was successfully allocated. On success, open file
42 * descriptors for the pty and tty sides and the name of the tty side are
43 * returned (the buffer must be able to hold at least 64 characters).
44 */
45
46int
47pty_allocate(int *ptyfd, int *ttyfd, char *namebuf, size_t namebuflen)
48{
49 char buf[64];
50 int i;
51
52 i = openpty(ptyfd, ttyfd, buf, NULL, NULL);
53 if (i == -1) {
54 error("openpty: %.100s", strerror(errno));
55 return 0;
56 }
57 strlcpy(namebuf, buf, namebuflen); /* possible truncation */
58 return 1;
59}
60
61/* Releases the tty. Its ownership is returned to root, and permissions to 0666. */
62
63void
64pty_release(const char *tty)
65{
66 if (chown(tty, (uid_t) 0, (gid_t) 0) == -1)
67 error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
68 if (chmod(tty, (mode_t) 0666) == -1)
69 error("chmod %.100s 0666 failed: %.100s", tty, strerror(errno));
70}
71
72/* Makes the tty the process's controlling tty and sets it to sane modes. */
73
74void
75pty_make_controlling_tty(int *ttyfd, const char *tty)
76{
77 int fd;
78
79 /* First disconnect from the old controlling tty. */
80#ifdef TIOCNOTTY
81 fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
82 if (fd >= 0) {
83 (void) ioctl(fd, TIOCNOTTY, NULL);
84 close(fd);
85 }
86#endif /* TIOCNOTTY */
87 if (setsid() == -1)
88 error("setsid: %.100s", strerror(errno));
89
90 /*
91 * Verify that we are successfully disconnected from the controlling
92 * tty.
93 */
94 fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
95 if (fd >= 0) {
96 error("Failed to disconnect from controlling tty.");
97 close(fd);
98 }
99 /* Make it our controlling tty. */
100#ifdef TIOCSCTTY
101 debug("Setting controlling tty using TIOCSCTTY.");
102 if (ioctl(*ttyfd, TIOCSCTTY, NULL) == -1)
103 error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
104#endif /* TIOCSCTTY */
105 fd = open(tty, O_RDWR);
106 if (fd == -1)
107 error("%.100s: %.100s", tty, strerror(errno));
108 else
109 close(fd);
110
111 /* Verify that we now have a controlling tty. */
112 fd = open(_PATH_TTY, O_WRONLY);
113 if (fd == -1)
114 error("open /dev/tty failed - could not set controlling tty: %.100s",
115 strerror(errno));
116 else
117 close(fd);
118}
119
120/* Changes the window size associated with the pty. */
121
122void
123pty_change_window_size(int ptyfd, u_int row, u_int col,
124 u_int xpixel, u_int ypixel)
125{
126 struct winsize w;
127
128 /* may truncate u_int -> u_short */
129 w.ws_row = row;
130 w.ws_col = col;
131 w.ws_xpixel = xpixel;
132 w.ws_ypixel = ypixel;
133 (void) ioctl(ptyfd, TIOCSWINSZ, &w);
134}
135
136void
137pty_setowner(struct passwd *pw, const char *tty)
138{
139 struct group *grp;
140 gid_t gid;
141 mode_t mode;
142 struct stat st;
143
144 /* Determine the group to make the owner of the tty. */
145 grp = getgrnam("tty");
146 if (grp == NULL)
147 fatal("no tty group");
148 gid = (grp != NULL) ? grp->gr_gid : pw->pw_gid;
149 mode = (grp != NULL) ? 0620 : 0600;
150
151 /*
152 * Change owner and mode of the tty as required.
153 * Warn but continue if filesystem is read-only and the uids match/
154 * tty is owned by root.
155 */
156 if (stat(tty, &st) == -1)
157 fatal("stat(%.100s) failed: %.100s", tty,
158 strerror(errno));
159
160 if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
161 if (chown(tty, pw->pw_uid, gid) == -1) {
162 if (errno == EROFS &&
163 (st.st_uid == pw->pw_uid || st.st_uid == 0))
164 debug("chown(%.100s, %u, %u) failed: %.100s",
165 tty, (u_int)pw->pw_uid, (u_int)gid,
166 strerror(errno));
167 else
168 fatal("chown(%.100s, %u, %u) failed: %.100s",
169 tty, (u_int)pw->pw_uid, (u_int)gid,
170 strerror(errno));
171 }
172 }
173
174 if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
175 if (chmod(tty, mode) == -1) {
176 if (errno == EROFS &&
177 (st.st_mode & (S_IRGRP | S_IROTH)) == 0)
178 debug("chmod(%.100s, 0%o) failed: %.100s",
179 tty, (u_int)mode, strerror(errno));
180 else
181 fatal("chmod(%.100s, 0%o) failed: %.100s",
182 tty, (u_int)mode, strerror(errno));
183 }
184 }
185}
186
187/* Disconnect from the controlling tty. */
188void
189disconnect_controlling_tty(void)
190{
191 int fd;
192
193 if ((fd = open(_PATH_TTY, O_RDWR | O_NOCTTY)) >= 0) {
194 (void) ioctl(fd, TIOCNOTTY, NULL);
195 close(fd);
196 }
197}