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 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 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 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 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 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 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