crypto/openssh/sshpty.c

   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 }