sshpty.c

   1 /* $OpenBSD: sshpty.c,v 1.26 2006/08/03 03:34:42 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 <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 /*
  50  * Allocates and opens a pty.  Returns 0 if no pty could be allocated, or
  51  * nonzero if a pty was successfully allocated.  On success, open file
  52  * descriptors for the pty and tty sides and the name of the tty side are
  53  * returned (the buffer must be able to hold at least 64 characters).
  54  */
  55
  56 int
  57 pty_allocate(int *ptyfd, int *ttyfd, char *namebuf, size_t namebuflen)
  58 {
  59         /* openpty(3) exists in OSF/1 and some other os'es */
  60         char *name;
  61         int i;
  62
  63         i = openpty(ptyfd, ttyfd, NULL, NULL, NULL);
  64         if (i < 0) {
  65                 error("openpty: %.100s", strerror(errno));
  66                 return 0;
  67         }
  68         name = ttyname(*ttyfd);
  69         if (!name)
  70                 fatal("openpty returns device for which ttyname fails.");
  71
  72         strlcpy(namebuf, name, namebuflen);     /* possible truncation */
  73         return 1;
  74 }
  75
  76 /* Releases the tty.  Its ownership is returned to root, and permissions to 0666. */
  77
  78 void
  79 pty_release(const char *tty)
  80 {
  81         if (chown(tty, (uid_t) 0, (gid_t) 0) < 0)
  82                 error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
  83         if (chmod(tty, (mode_t) 0666) < 0)
  84                 error("chmod %.100s 0666 failed: %.100s", tty, strerror(errno));
  85 }
  86
  87 /* Makes the tty the process's controlling tty and sets it to sane modes. */
  88
  89 void
  90 pty_make_controlling_tty(int *ttyfd, const char *tty)
  91 {
  92         int fd;
  93 #ifdef USE_VHANGUP
  94         void *old;
  95 #endif /* USE_VHANGUP */
  96
  97 #ifdef _UNICOS
  98         if (setsid() < 0)
  99                 error("setsid: %.100s", strerror(errno));
 100
 101         fd = open(tty, O_RDWR|O_NOCTTY);
 102         if (fd != -1) {
 103                 signal(SIGHUP, SIG_IGN);
 104                 ioctl(fd, TCVHUP, (char *)NULL);
 105                 signal(SIGHUP, SIG_DFL);
 106                 setpgid(0, 0);
 107                 close(fd);
 108         } else {
 109                 error("Failed to disconnect from controlling tty.");
 110         }
 111
 112         debug("Setting controlling tty using TCSETCTTY.");
 113         ioctl(*ttyfd, TCSETCTTY, NULL);
 114         fd = open("/dev/tty", O_RDWR);
 115         if (fd < 0)
 116                 error("%.100s: %.100s", tty, strerror(errno));
 117         close(*ttyfd);
 118         *ttyfd = fd;
 119 #else /* _UNICOS */
 120
 121         /* First disconnect from the old controlling tty. */
 122 #ifdef TIOCNOTTY
 123         fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
 124         if (fd >= 0) {
 125                 (void) ioctl(fd, TIOCNOTTY, NULL);
 126                 close(fd);
 127         }
 128 #endif /* TIOCNOTTY */
 129         if (setsid() < 0)
 130                 error("setsid: %.100s", strerror(errno));
 131
 132         /*
 133          * Verify that we are successfully disconnected from the controlling
 134          * tty.
 135          */
 136         fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
 137         if (fd >= 0) {
 138                 error("Failed to disconnect from controlling tty.");
 139                 close(fd);
 140         }
 141         /* Make it our controlling tty. */
 142 #ifdef TIOCSCTTY
 143         debug("Setting controlling tty using TIOCSCTTY.");
 144         if (ioctl(*ttyfd, TIOCSCTTY, NULL) < 0)
 145                 error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
 146 #endif /* TIOCSCTTY */
 147 #ifdef NEED_SETPGRP
 148         if (setpgrp(0,0) < 0)
 149                 error("SETPGRP %s",strerror(errno));
 150 #endif /* NEED_SETPGRP */
 151 #ifdef USE_VHANGUP
 152         old = signal(SIGHUP, SIG_IGN);
 153         vhangup();
 154         signal(SIGHUP, old);
 155 #endif /* USE_VHANGUP */
 156         fd = open(tty, O_RDWR);
 157         if (fd < 0) {
 158                 error("%.100s: %.100s", tty, strerror(errno));
 159         } else {
 160 #ifdef USE_VHANGUP
 161                 close(*ttyfd);
 162                 *ttyfd = fd;
 163 #else /* USE_VHANGUP */
 164                 close(fd);
 165 #endif /* USE_VHANGUP */
 166         }
 167         /* Verify that we now have a controlling tty. */
 168         fd = open(_PATH_TTY, O_WRONLY);
 169         if (fd < 0)
 170                 error("open /dev/tty failed - could not set controlling tty: %.100s",
 171                     strerror(errno));
 172         else
 173                 close(fd);
 174 #endif /* _UNICOS */
 175 }
 176
 177 /* Changes the window size associated with the pty. */
 178
 179 void
 180 pty_change_window_size(int ptyfd, u_int row, u_int col,
 181         u_int xpixel, u_int ypixel)
 182 {
 183         struct winsize w;
 184
 185         /* may truncate u_int -> u_short */
 186         w.ws_row = row;
 187         w.ws_col = col;
 188         w.ws_xpixel = xpixel;
 189         w.ws_ypixel = ypixel;
 190         (void) ioctl(ptyfd, TIOCSWINSZ, &w);
 191 }
 192
 193 void
 194 pty_setowner(struct passwd *pw, const char *tty)
 195 {
 196         struct group *grp;
 197         gid_t gid;
 198         mode_t mode;
 199         struct stat st;
 200
 201         /* Determine the group to make the owner of the tty. */
 202         grp = getgrnam("tty");
 203         if (grp) {
 204                 gid = grp->gr_gid;
 205                 mode = S_IRUSR | S_IWUSR | S_IWGRP;
 206         } else {
 207                 gid = pw->pw_gid;
 208                 mode = S_IRUSR | S_IWUSR | S_IWGRP | S_IWOTH;
 209         }
 210
 211         /*
 212          * Change owner and mode of the tty as required.
 213          * Warn but continue if filesystem is read-only and the uids match/
 214          * tty is owned by root.
 215          */
 216         if (stat(tty, &st))
 217                 fatal("stat(%.100s) failed: %.100s", tty,
 218                     strerror(errno));
 219
 220 #ifdef WITH_SELINUX
 221         ssh_selinux_setup_pty(pw->pw_name, tty);
 222 #endif
 223
 224         if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
 225                 if (chown(tty, pw->pw_uid, gid) < 0) {
 226                         if (errno == EROFS &&
 227                             (st.st_uid == pw->pw_uid || st.st_uid == 0))
 228                                 debug("chown(%.100s, %u, %u) failed: %.100s",
 229                                     tty, (u_int)pw->pw_uid, (u_int)gid,
 230                                     strerror(errno));
 231                         else
 232                                 fatal("chown(%.100s, %u, %u) failed: %.100s",
 233                                     tty, (u_int)pw->pw_uid, (u_int)gid,
 234                                     strerror(errno));
 235                 }
 236         }
 237
 238         if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
 239                 if (chmod(tty, mode) < 0) {
 240                         if (errno == EROFS &&
 241                             (st.st_mode & (S_IRGRP | S_IROTH)) == 0)
 242                                 debug("chmod(%.100s, 0%o) failed: %.100s",
 243                                     tty, (u_int)mode, strerror(errno));
 244                         else
 245                                 fatal("chmod(%.100s, 0%o) failed: %.100s",
 246                                     tty, (u_int)mode, strerror(errno));
 247                 }
 248         }
 249 }