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      1 /* $OpenBSD: sshpty.c,v 1.31 2016/11/29 03:54:50 dtucker Exp $ */
      2 /*
      3  * Author: Tatu Ylonen <ylo (at) cs.hut.fi>
      4  * Copyright (c) 1995 Tatu Ylonen <ylo (at) 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
     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 < 0) {
     72 		error("openpty: %.100s", strerror(errno));
     73 		return 0;
     74 	}
     75 #ifdef ANDROID
     76 	if (ptsname_r(*ptyfd, namebuf, namebuflen)) {
     77 		fatal("openpty ptsname failed.");
     78 		close(*ptyfd);
     79 		*ptyfd = -1;
     80 		return -1;
     81 	}
     82 	return 1;
     83 #else
     84 	name = ttyname(*ttyfd);
     85 	if (!name)
     86 		fatal("openpty returns device for which ttyname fails.");
     87 
     88 	strlcpy(namebuf, name, namebuflen);	/* possible truncation */
     89 	return 1;
     90 #endif
     91 }
     92 
     93 /* Releases the tty.  Its ownership is returned to root, and permissions to 0666. */
     94 
     95 void
     96 pty_release(const char *tty)
     97 {
     98 #if !defined(__APPLE_PRIVPTY__) && !defined(HAVE_OPENPTY)
     99 	if (chown(tty, (uid_t) 0, (gid_t) 0) < 0)
    100 		error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
    101 	if (chmod(tty, (mode_t) 0666) < 0)
    102 		error("chmod %.100s 0666 failed: %.100s", tty, strerror(errno));
    103 #endif /* !__APPLE_PRIVPTY__ && !HAVE_OPENPTY */
    104 }
    105 
    106 /* Makes the tty the process's controlling tty and sets it to sane modes. */
    107 
    108 void
    109 pty_make_controlling_tty(int *ttyfd, const char *tty)
    110 {
    111 	int fd;
    112 
    113 #ifdef _UNICOS
    114 	if (setsid() < 0)
    115 		error("setsid: %.100s", strerror(errno));
    116 
    117 	fd = open(tty, O_RDWR|O_NOCTTY);
    118 	if (fd != -1) {
    119 		signal(SIGHUP, SIG_IGN);
    120 		ioctl(fd, TCVHUP, (char *)NULL);
    121 		signal(SIGHUP, SIG_DFL);
    122 		setpgid(0, 0);
    123 		close(fd);
    124 	} else {
    125 		error("Failed to disconnect from controlling tty.");
    126 	}
    127 
    128 	debug("Setting controlling tty using TCSETCTTY.");
    129 	ioctl(*ttyfd, TCSETCTTY, NULL);
    130 	fd = open("/dev/tty", O_RDWR);
    131 	if (fd < 0)
    132 		error("%.100s: %.100s", tty, strerror(errno));
    133 	close(*ttyfd);
    134 	*ttyfd = fd;
    135 #else /* _UNICOS */
    136 
    137 	/* First disconnect from the old controlling tty. */
    138 #ifdef TIOCNOTTY
    139 	fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
    140 	if (fd >= 0) {
    141 		(void) ioctl(fd, TIOCNOTTY, NULL);
    142 		close(fd);
    143 	}
    144 #endif /* TIOCNOTTY */
    145 	if (setsid() < 0)
    146 		error("setsid: %.100s", strerror(errno));
    147 
    148 	/*
    149 	 * Verify that we are successfully disconnected from the controlling
    150 	 * tty.
    151 	 */
    152 	fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
    153 	if (fd >= 0) {
    154 		error("Failed to disconnect from controlling tty.");
    155 		close(fd);
    156 	}
    157 	/* Make it our controlling tty. */
    158 #ifdef TIOCSCTTY
    159 	debug("Setting controlling tty using TIOCSCTTY.");
    160 	if (ioctl(*ttyfd, TIOCSCTTY, NULL) < 0)
    161 		error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
    162 #endif /* TIOCSCTTY */
    163 #ifdef NEED_SETPGRP
    164 	if (setpgrp(0,0) < 0)
    165 		error("SETPGRP %s",strerror(errno));
    166 #endif /* NEED_SETPGRP */
    167 	fd = open(tty, O_RDWR);
    168 	if (fd < 0)
    169 		error("%.100s: %.100s", tty, strerror(errno));
    170 	else
    171 		close(fd);
    172 
    173 	/* Verify that we now have a controlling tty. */
    174 	fd = open(_PATH_TTY, O_WRONLY);
    175 	if (fd < 0)
    176 		error("open /dev/tty failed - could not set controlling tty: %.100s",
    177 		    strerror(errno));
    178 	else
    179 		close(fd);
    180 #endif /* _UNICOS */
    181 }
    182 
    183 /* Changes the window size associated with the pty. */
    184 
    185 void
    186 pty_change_window_size(int ptyfd, u_int row, u_int col,
    187 	u_int xpixel, u_int ypixel)
    188 {
    189 	struct winsize w;
    190 
    191 	/* may truncate u_int -> u_short */
    192 	w.ws_row = row;
    193 	w.ws_col = col;
    194 	w.ws_xpixel = xpixel;
    195 	w.ws_ypixel = ypixel;
    196 	(void) ioctl(ptyfd, TIOCSWINSZ, &w);
    197 }
    198 
    199 void
    200 pty_setowner(struct passwd *pw, const char *tty)
    201 {
    202 	struct group *grp;
    203 	gid_t gid;
    204 	mode_t mode;
    205 	struct stat st;
    206 
    207 	/* Determine the group to make the owner of the tty. */
    208 	grp = getgrnam("tty");
    209 	gid = (grp != NULL) ? grp->gr_gid : pw->pw_gid;
    210 	mode = (grp != NULL) ? 0620 : 0600;
    211 
    212 	/*
    213 	 * Change owner and mode of the tty as required.
    214 	 * Warn but continue if filesystem is read-only and the uids match/
    215 	 * tty is owned by root.
    216 	 */
    217 	if (stat(tty, &st))
    218 		fatal("stat(%.100s) failed: %.100s", tty,
    219 		    strerror(errno));
    220 
    221 #ifdef WITH_SELINUX
    222 	ssh_selinux_setup_pty(pw->pw_name, tty);
    223 #endif
    224 
    225 	if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
    226 		if (chown(tty, pw->pw_uid, gid) < 0) {
    227 			if (errno == EROFS &&
    228 			    (st.st_uid == pw->pw_uid || st.st_uid == 0))
    229 				debug("chown(%.100s, %u, %u) failed: %.100s",
    230 				    tty, (u_int)pw->pw_uid, (u_int)gid,
    231 				    strerror(errno));
    232 			else
    233 				fatal("chown(%.100s, %u, %u) failed: %.100s",
    234 				    tty, (u_int)pw->pw_uid, (u_int)gid,
    235 				    strerror(errno));
    236 		}
    237 	}
    238 
    239 	if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
    240 		if (chmod(tty, mode) < 0) {
    241 			if (errno == EROFS &&
    242 			    (st.st_mode & (S_IRGRP | S_IROTH)) == 0)
    243 				debug("chmod(%.100s, 0%o) failed: %.100s",
    244 				    tty, (u_int)mode, strerror(errno));
    245 			else
    246 				fatal("chmod(%.100s, 0%o) failed: %.100s",
    247 				    tty, (u_int)mode, strerror(errno));
    248 		}
    249 	}
    250 }
    251 
    252 /* Disconnect from the controlling tty. */
    253 void
    254 disconnect_controlling_tty(void)
    255 {
    256 #ifdef TIOCNOTTY
    257 	int fd;
    258 
    259 	if ((fd = open(_PATH_TTY, O_RDWR | O_NOCTTY)) >= 0) {
    260 		(void) ioctl(fd, TIOCNOTTY, NULL);
    261 		close(fd);
    262 	}
    263 #endif /* TIOCNOTTY */
    264 }
    265