sshpty.c

   1 /* $OpenBSD: sshpty.c,v 1.24 2006/07/17 01:31:10 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 <termios.h>
  30 #ifdef HAVE_UTIL_H
  31 # include <util.h>
  32 #endif /* HAVE_UTIL_H */
  33 #include <unistd.h>
  34
  35 #include "sshpty.h"
  36 #include "log.h"
  37 #include "misc.h"
  38
  39 #ifdef HAVE_PTY_H
  40 # include <pty.h>
  41 #endif
  42
  43 #ifndef O_NOCTTY
  44 #define O_NOCTTY 0
  45 #endif
  46
  47 /*
  48  * Allocates and opens a pty.  Returns 0 if no pty could be allocated, or
  49  * nonzero if a pty was successfully allocated.  On success, open file
  50  * descriptors for the pty and tty sides and the name of the tty side are
  51  * returned (the buffer must be able to hold at least 64 characters).
  52  */
  53
  54 int
  55 pty_allocate(int *ptyfd, int *ttyfd, char *namebuf, size_t namebuflen)
  56 {
  57         /* openpty(3) exists in OSF/1 and some other os'es */
  58         char *name;
  59         int i;
  60
  61         i = openpty(ptyfd, ttyfd, NULL, NULL, NULL);
  62         if (i < 0) {
  63                 error("openpty: %.100s", strerror(errno));
  64                 return 0;
  65         }
  66         name = ttyname(*ttyfd);
  67         if (!name)
  68                 fatal("openpty returns device for which ttyname fails.");
  69
  70         strlcpy(namebuf, name, namebuflen);     /* possible truncation */
  71         return 1;
  72 }
  73
  74 /* Releases the tty.  Its ownership is returned to root, and permissions to 0666. */
  75
  76 void
  77 pty_release(const char *tty)
  78 {
  79         if (chown(tty, (uid_t) 0, (gid_t) 0) < 0)
  80                 error("chown %.100s 0 0 failed: %.100s", tty, strerror(errno));
  81         if (chmod(tty, (mode_t) 0666) < 0)
  82                 error("chmod %.100s 0666 failed: %.100s", tty, strerror(errno));
  83 }
  84
  85 /* Makes the tty the process's controlling tty and sets it to sane modes. */
  86
  87 void
  88 pty_make_controlling_tty(int *ttyfd, const char *tty)
  89 {
  90         int fd;
  91 #ifdef USE_VHANGUP
  92         void *old;
  93 #endif /* USE_VHANGUP */
  94
  95 #ifdef _UNICOS
  96         if (setsid() < 0)
  97                 error("setsid: %.100s", strerror(errno));
  98
  99         fd = open(tty, O_RDWR|O_NOCTTY);
 100         if (fd != -1) {
 101                 signal(SIGHUP, SIG_IGN);
 102                 ioctl(fd, TCVHUP, (char *)NULL);
 103                 signal(SIGHUP, SIG_DFL);
 104                 setpgid(0, 0);
 105                 close(fd);
 106         } else {
 107                 error("Failed to disconnect from controlling tty.");
 108         }
 109
 110         debug("Setting controlling tty using TCSETCTTY.");
 111         ioctl(*ttyfd, TCSETCTTY, NULL);
 112         fd = open("/dev/tty", O_RDWR);
 113         if (fd < 0)
 114                 error("%.100s: %.100s", tty, strerror(errno));
 115         close(*ttyfd);
 116         *ttyfd = fd;
 117 #else /* _UNICOS */
 118
 119         /* First disconnect from the old controlling tty. */
 120 #ifdef TIOCNOTTY
 121         fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
 122         if (fd >= 0) {
 123                 (void) ioctl(fd, TIOCNOTTY, NULL);
 124                 close(fd);
 125         }
 126 #endif /* TIOCNOTTY */
 127         if (setsid() < 0)
 128                 error("setsid: %.100s", strerror(errno));
 129
 130         /*
 131          * Verify that we are successfully disconnected from the controlling
 132          * tty.
 133          */
 134         fd = open(_PATH_TTY, O_RDWR | O_NOCTTY);
 135         if (fd >= 0) {
 136                 error("Failed to disconnect from controlling tty.");
 137                 close(fd);
 138         }
 139         /* Make it our controlling tty. */
 140 #ifdef TIOCSCTTY
 141         debug("Setting controlling tty using TIOCSCTTY.");
 142         if (ioctl(*ttyfd, TIOCSCTTY, NULL) < 0)
 143                 error("ioctl(TIOCSCTTY): %.100s", strerror(errno));
 144 #endif /* TIOCSCTTY */
 145 #ifdef NEED_SETPGRP
 146         if (setpgrp(0,0) < 0)
 147                 error("SETPGRP %s",strerror(errno));
 148 #endif /* NEED_SETPGRP */
 149 #ifdef USE_VHANGUP
 150         old = signal(SIGHUP, SIG_IGN);
 151         vhangup();
 152         signal(SIGHUP, old);
 153 #endif /* USE_VHANGUP */
 154         fd = open(tty, O_RDWR);
 155         if (fd < 0) {
 156                 error("%.100s: %.100s", tty, strerror(errno));
 157         } else {
 158 #ifdef USE_VHANGUP
 159                 close(*ttyfd);
 160                 *ttyfd = fd;
 161 #else /* USE_VHANGUP */
 162                 close(fd);
 163 #endif /* USE_VHANGUP */
 164         }
 165         /* Verify that we now have a controlling tty. */
 166         fd = open(_PATH_TTY, O_WRONLY);
 167         if (fd < 0)
 168                 error("open /dev/tty failed - could not set controlling tty: %.100s",
 169                     strerror(errno));
 170         else
 171                 close(fd);
 172 #endif /* _UNICOS */
 173 }
 174
 175 /* Changes the window size associated with the pty. */
 176
 177 void
 178 pty_change_window_size(int ptyfd, u_int row, u_int col,
 179         u_int xpixel, u_int ypixel)
 180 {
 181         struct winsize w;
 182
 183         /* may truncate u_int -> u_short */
 184         w.ws_row = row;
 185         w.ws_col = col;
 186         w.ws_xpixel = xpixel;
 187         w.ws_ypixel = ypixel;
 188         (void) ioctl(ptyfd, TIOCSWINSZ, &w);
 189 }
 190
 191 void
 192 pty_setowner(struct passwd *pw, const char *tty)
 193 {
 194         struct group *grp;
 195         gid_t gid;
 196         mode_t mode;
 197         struct stat st;
 198
 199         /* Determine the group to make the owner of the tty. */
 200         grp = getgrnam("tty");
 201         if (grp) {
 202                 gid = grp->gr_gid;
 203                 mode = S_IRUSR | S_IWUSR | S_IWGRP;
 204         } else {
 205                 gid = pw->pw_gid;
 206                 mode = S_IRUSR | S_IWUSR | S_IWGRP | S_IWOTH;
 207         }
 208
 209         /*
 210          * Change owner and mode of the tty as required.
 211          * Warn but continue if filesystem is read-only and the uids match/
 212          * tty is owned by root.
 213          */
 214         if (stat(tty, &st))
 215                 fatal("stat(%.100s) failed: %.100s", tty,
 216                     strerror(errno));
 217
 218 #ifdef WITH_SELINUX
 219         ssh_selinux_setup_pty(pw->pw_name, tty);
 220 #endif
 221
 222         if (st.st_uid != pw->pw_uid || st.st_gid != gid) {
 223                 if (chown(tty, pw->pw_uid, gid) < 0) {
 224                         if (errno == EROFS &&
 225                             (st.st_uid == pw->pw_uid || st.st_uid == 0))
 226                                 debug("chown(%.100s, %u, %u) failed: %.100s",
 227                                     tty, (u_int)pw->pw_uid, (u_int)gid,
 228                                     strerror(errno));
 229                         else
 230                                 fatal("chown(%.100s, %u, %u) failed: %.100s",
 231                                     tty, (u_int)pw->pw_uid, (u_int)gid,
 232                                     strerror(errno));
 233                 }
 234         }
 235
 236         if ((st.st_mode & (S_IRWXU|S_IRWXG|S_IRWXO)) != mode) {
 237                 if (chmod(tty, mode) < 0) {
 238                         if (errno == EROFS &&
 239                             (st.st_mode & (S_IRGRP | S_IROTH)) == 0)
 240                                 debug("chmod(%.100s, 0%o) failed: %.100s",
 241                                     tty, (u_int)mode, strerror(errno));
 242                         else
 243                                 fatal("chmod(%.100s, 0%o) failed: %.100s",
 244                                     tty, (u_int)mode, strerror(errno));
 245                 }
 246         }
 247 }