sshpty.c

   1 /* $OpenBSD: sshpty.c,v 1.25 2006/07/22 20:48:23 stevesk 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/ioctl.h>
  18 #include <sys/types.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 <string.h>
  30 #include <termios.h>
  31 #ifdef HAVE_UTIL_H
  32 # include <util.h>
  33 #endif /* HAVE_UTIL_H */
  34 #include <unistd.h>
  35
  36 #include "sshpty.h"
  37 #include "log.h"
  38 #include "misc.h"
  39
  40 #ifdef HAVE_PTY_H
  41 # include <pty.h>
  42 #endif
  43
  44 #ifndef O_NOCTTY
  45 #define O_NOCTTY 0
  46 #endif
  47
  48 /*
  49  * Allocates and opens a pty.  Returns 0 if no pty could be allocated, or
  50  * nonzero if a pty was successfully allocated.  On success, open file
  51  * descriptors for the pty and tty sides and the name of the tty side are
  52  * returned (the buffer must be able to hold at least 64 characters).
  53  */
  54
  55 int
  56 pty_allocate(int *ptyfd, int *ttyfd, char *namebuf, size_t namebuflen)
  57 {
  58         /* openpty(3) exists in OSF/1 and some other os'es */
  59         char *name;
  60         int i;
  61
  62         i = openpty(ptyfd, ttyfd, NULL, NULL, NULL);
  63         if (i < 0) {
  64                 error("openpty: %.100s", strerror(errno));
  65                 return 0;
  66         }
  67         name = ttyname(*ttyfd);
  68         if (!name)
  69                 fatal("openpty returns device for which ttyname fails.");
  70
  71         strlcpy(namebuf, name, namebuflen);     /* possible truncation */
  72         return 1;
  73 }
  74
  75 /* Releases the tty.  Its ownership is returned to root, and permissions to 0666. */
  76
  77 void
  78 pty_release(const char *tty)
  79 {
  80         if (chown(tty, (uid_t) 0, (gid_t) 0) < 0)
  81                 error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
  82         if (chmod(tty, (mode_t) 0666) < 0)
  83                 error("chmod %.100s 0666 failed: %.100s", tty, strerror(errno));
  84 }
  85
  86 /* Makes the tty the process's controlling tty and sets it to sane modes. */
  87
  88 void
  89 pty_make_controlling_tty(int *ttyfd, const char *tty)
  90 {
  91         int fd;
  92 #ifdef USE_VHANGUP
  93         void *old;
  94 #endif /* USE_VHANGUP */
  95
  96 #ifdef _UNICOS
  97         if (setsid() < 0)
  98                 error("setsid: %.100s", strerror(errno));
  99
 100         fd = open(tty, O_RDWR|O_NOCTTY);
 101         if (fd != -1) {
 102                 signal(SIGHUP, SIG_IGN);
 103                 ioctl(fd, TCVHUP, (char *)NULL);
 104                 signal(SIGHUP, SIG_DFL);
 105                 setpgid(0, 0);
 106                 close(fd);
 107         } else {
 108                 error("Failed to disconnect from controlling tty.");
 109         }
 110
 111         debug("Setting controlling tty using TCSETCTTY.");
 112         ioctl(*ttyfd, TCSETCTTY, NULL);
 113         fd = open("/dev/tty", O_RDWR);
 114         if (fd < 0)
 115                 error("%.100s: %.100s", tty, strerror(errno));
 116         close(*ttyfd);
 117         *ttyfd = fd;
 118 #else /* _UNICOS */
 119
 120         /* First disconnect from the old controlling tty. */
 121 #ifdef TIOCNOTTY
 122         fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
 123         if (fd >= 0) {
 124                 (void) ioctl(fd, TIOCNOTTY, NULL);
 125                 close(fd);
 126         }
 127 #endif /* TIOCNOTTY */
 128         if (setsid() < 0)
 129                 error("setsid: %.100s", strerror(errno));
 130
 131         /*
 132          * Verify that we are successfully disconnected from the controlling
 133          * tty.
 134          */
 135         fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
 136         if (fd >= 0) {
 137                 error("Failed to disconnect from controlling tty.");
 138                 close(fd);
 139         }
 140         /* Make it our controlling tty. */
 141 #ifdef TIOCSCTTY
 142         debug("Setting controlling tty using TIOCSCTTY.");
 143         if (ioctl(*ttyfd, TIOCSCTTY, NULL) < 0)
 144                 error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
 145 #endif /* TIOCSCTTY */
 146 #ifdef NEED_SETPGRP
 147         if (setpgrp(0,0) < 0)
 148                 error("SETPGRP %s",strerror(errno));
 149 #endif /* NEED_SETPGRP */
 150 #ifdef USE_VHANGUP
 151         old = signal(SIGHUP, SIG_IGN);
 152         vhangup();
 153         signal(SIGHUP, old);
 154 #endif /* USE_VHANGUP */
 155         fd = open(tty, O_RDWR);
 156         if (fd < 0) {
 157                 error("%.100s: %.100s", tty, strerror(errno));
 158         } else {
 159 #ifdef USE_VHANGUP
 160                 close(*ttyfd);
 161                 *ttyfd = fd;
 162 #else /* USE_VHANGUP */
 163                 close(fd);
 164 #endif /* USE_VHANGUP */
 165         }
 166         /* Verify that we now have a controlling tty. */
 167         fd = open(_PATH_TTY, O_WRONLY);
 168         if (fd < 0)
 169                 error("open /dev/tty failed - could not set controlling tty: %.100s",
 170                     strerror(errno));
 171         else
 172                 close(fd);
 173 #endif /* _UNICOS */
 174 }
 175
 176 /* Changes the window size associated with the pty. */
 177
 178 void
 179 pty_change_window_size(int ptyfd, u_int row, u_int col,
 180         u_int xpixel, u_int ypixel)
 181 {
 182         struct winsize w;
 183
 184         /* may truncate u_int -> u_short */
 185         w.ws_row = row;
 186         w.ws_col = col;
 187         w.ws_xpixel = xpixel;
 188         w.ws_ypixel = ypixel;
 189         (void) ioctl(ptyfd, TIOCSWINSZ, &w);
 190 }
 191
 192 void
 193 pty_setowner(struct passwd *pw, const char *tty)
 194 {
 195         struct group *grp;
 196         gid_t gid;
 197         mode_t mode;
 198         struct stat st;
 199
 200         /* Determine the group to make the owner of the tty. */
 201         grp = getgrnam("tty");
 202         if (grp) {
 203                 gid = grp->gr_gid;
 204                 mode = S_IRUSR | S_IWUSR | S_IWGRP;
 205         } else {
 206                 gid = pw->pw_gid;
 207                 mode = S_IRUSR | S_IWUSR | S_IWGRP | S_IWOTH;
 208         }
 209
 210         /*
 211          * Change owner and mode of the tty as required.
 212          * Warn but continue if filesystem is read-only and the uids match/
 213          * tty is owned by root.
 214          */
 215         if (stat(tty, &st))
 216                 fatal("stat(%.100s) failed: %.100s", tty,
 217                     strerror(errno));
 218
 219 #ifdef WITH_SELINUX
 220         ssh_selinux_setup_pty(pw->pw_name, tty);
 221 #endif
 222
 223         if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
 224                 if (chown(tty, pw->pw_uid, gid) < 0) {
 225                         if (errno == EROFS &&
 226                             (st.st_uid == pw->pw_uid || st.st_uid == 0))
 227                                 debug("chown(%.100s, %u, %u) failed: %.100s",
 228                                     tty, (u_int)pw->pw_uid, (u_int)gid,
 229                                     strerror(errno));
 230                         else
 231                                 fatal("chown(%.100s, %u, %u) failed: %.100s",
 232                                     tty, (u_int)pw->pw_uid, (u_int)gid,
 233                                     strerror(errno));
 234                 }
 235         }
 236
 237         if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
 238                 if (chmod(tty, mode) < 0) {
 239                         if (errno == EROFS &&
 240                             (st.st_mode & (S_IRGRP | S_IROTH)) == 0)
 241                                 debug("chmod(%.100s, 0%o) failed: %.100s",
 242                                     tty, (u_int)mode, strerror(errno));
 243                         else
 244                                 fatal("chmod(%.100s, 0%o) failed: %.100s",
 245                                     tty, (u_int)mode, strerror(errno));
 246                 }
 247         }
 248 }