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lookup-retry.c

/* hairy bits of Hurd file name lookup
   Copyright (C) 1992,1993,1994,1995,1996,1997,1999,2001,2002,2003,2005
      Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <hurd.h>
#include <hurd/lookup.h>
#include <hurd/term.h>
#include <hurd/paths.h>
#include <limits.h>
#include <fcntl.h>
#include <string.h>
#include "stdio-common/_itoa.h"

/* Translate the error from dir_lookup into the error the user sees.  */
static inline error_t
lookup_error (error_t error)
{
  switch (error)
    {
    case EOPNOTSUPP:
    case MIG_BAD_ID:
      /* These indicate that the server does not understand dir_lookup
       at all.  If it were a directory, it would, by definition.  */
      return ENOTDIR;
    default:
      return error;
    }
}

error_t
__hurd_file_name_lookup_retry (error_t (*use_init_port)
                           (int which, error_t (*operate) (file_t)),
                         file_t (*get_dtable_port) (int fd),
                         error_t (*lookup)
                           (file_t dir, char *name,
                          int flags, mode_t mode,
                          retry_type *do_retry, string_t retry_name,
                          mach_port_t *result),
                         enum retry_type doretry,
                         char retryname[1024],
                         int flags, mode_t mode,
                         file_t *result)
{
  error_t err;
  char *file_name;
  int nloops;

  error_t lookup_op (file_t startdir)
    {
      while (file_name[0] == '/')
      file_name++;

      return lookup_error ((*lookup) (startdir, file_name, flags, mode,
                              &doretry, retryname, result));
    }
  error_t reauthenticate (file_t unauth)
    {
      error_t err;
      mach_port_t ref = __mach_reply_port ();
      error_t reauth (auth_t auth)
      {
        return __auth_user_authenticate (auth, ref,
                                 MACH_MSG_TYPE_MAKE_SEND,
                                 result);
      }
      err = __io_reauthenticate (unauth, ref, MACH_MSG_TYPE_MAKE_SEND);
      if (! err)
      err = (*use_init_port) (INIT_PORT_AUTH, &reauth);
      __mach_port_destroy (__mach_task_self (), ref);
      __mach_port_deallocate (__mach_task_self (), unauth);
      return err;
    }

  if (! lookup)
    lookup = __dir_lookup;

  nloops = 0;
  err = 0;
  do
    {
      file_t startdir = MACH_PORT_NULL;
      int dirport = INIT_PORT_CWDIR;

      switch (doretry)
      {
      case FS_RETRY_REAUTH:
        if (err = reauthenticate (*result))
          return err;
        /* Fall through.  */

      case FS_RETRY_NORMAL:
        if (nloops++ >= SYMLOOP_MAX)
          {
            __mach_port_deallocate (__mach_task_self (), *result);
            return ELOOP;
          }

        /* An empty RETRYNAME indicates we have the final port.  */
        if (retryname[0] == '\0' &&
            /* If reauth'd, we must do one more retry on "" to give the new
             translator a chance to make a new port for us.  */
            doretry == FS_RETRY_NORMAL)
          {
            if (flags & O_NOFOLLOW)
            {
              /* In Linux, O_NOFOLLOW means to reject symlinks.  If we
                 did an O_NOLINK lookup above and io_stat here to check
                 for S_IFLNK, a translator like firmlink could easily
                 spoof this check by not showing S_IFLNK, but in fact
                 redirecting the lookup to some other name
                 (i.e. opening the very same holes a symlink would).

                 Instead we do an O_NOTRANS lookup above, and stat the
                 underlying node: if it has a translator set, and its
                 owner is not root (st_uid 0) then we reject it.
                 Since the motivation for this feature is security, and
                 that security presumes we trust the containing
                 directory, this check approximates the security of
                 refusing symlinks while accepting mount points.
                 Note that we actually permit something Linux doesn't:
                 we follow root-owned symlinks; if that is deemed
                 undesireable, we can add a final check for that
                 one exception to our general translator-based rule.  */
              struct stat64 st;
              err = __io_stat (*result, &st);
              if (!err
                  && (st.st_mode & (S_IPTRANS|S_IATRANS)))
                {
                  if (st.st_uid != 0)
                  err = ENOENT;
                  else if (st.st_mode & S_IPTRANS)
                  {
                    char buf[1024];
                    char *trans = buf;
                    size_t translen = sizeof buf;
                    err = __file_get_translator (*result,
                                           &trans, &translen);
                    if (!err
                        && translen > sizeof _HURD_SYMLINK
                        && !memcmp (trans,
                                _HURD_SYMLINK, sizeof _HURD_SYMLINK))
                      err = ENOENT;
                  }
                }
            }

            /* We got a successful translation.  Now apply any open-time
             action flags we were passed.  */

            if (!err && (flags & O_TRUNC)) /* Asked to truncate the file.  */
            err = __file_set_size (*result, 0);

            if (err)
            __mach_port_deallocate (__mach_task_self (), *result);
            return err;
          }

        startdir = *result;
        file_name = retryname;
        break;

      case FS_RETRY_MAGICAL:
        switch (retryname[0])
          {
          case '/':
            dirport = INIT_PORT_CRDIR;
            if (*result != MACH_PORT_NULL)
            __mach_port_deallocate (__mach_task_self (), *result);
            if (nloops++ >= SYMLOOP_MAX)
            return ELOOP;
            file_name = &retryname[1];
            break;

          case 'f':
            if (retryname[1] == 'd' && retryname[2] == '/')
            {
              int fd;
              char *end;
              int save = errno;
              errno = 0;
              fd = (int) strtoul (&retryname[3], &end, 10);
              if (end == NULL || errno || /* Malformed number.  */
                  /* Check for excess text after the number.  A slash
                   is valid; it ends the component.  Anything else
                   does not name a numeric file descriptor.  */
                  (*end != '/' && *end != '\0'))
                {
                  errno = save;
                  return ENOENT;
                }
              if (! get_dtable_port)
                err = EGRATUITOUS;
              else
                {
                  *result = (*get_dtable_port) (fd);
                  if (*result == MACH_PORT_NULL)
                  {
                    /* If the name was a proper number, but the file
                       descriptor does not exist, we return EBADF instead
                       of ENOENT.  */
                    err = errno;
                    errno = save;
                  }
                }
              errno = save;
              if (err)
                return err;
              if (*end == '\0')
                return 0;
              else
                {
                  /* Do a normal retry on the remaining components.  */
                  startdir = *result;
                  file_name = end + 1; /* Skip the slash.  */
                  break;
                }
            }
            else
            goto bad_magic;
            break;

          case 'm':
            if (retryname[1] == 'a' && retryname[2] == 'c' &&
              retryname[3] == 'h' && retryname[4] == 't' &&
              retryname[5] == 'y' && retryname[6] == 'p' &&
              retryname[7] == 'e')
            {
              error_t err;
              struct host_basic_info hostinfo;
              mach_msg_type_number_t hostinfocnt = HOST_BASIC_INFO_COUNT;
              char *p;
              /* XXX want client's host */
              if (err = __host_info (__mach_host_self (), HOST_BASIC_INFO,
                               (integer_t *) &hostinfo,
                               &hostinfocnt))
                return err;
              if (hostinfocnt != HOST_BASIC_INFO_COUNT)
                return EGRATUITOUS;
              p = _itoa (hostinfo.cpu_subtype, &retryname[8], 10, 0);
              *--p = '/';
              p = _itoa (hostinfo.cpu_type, &retryname[8], 10, 0);
              if (p < retryname)
                abort ();     /* XXX write this right if this ever happens */
              if (p > retryname)
                strcpy (retryname, p);
              startdir = *result;
            }
            else
            goto bad_magic;
            break;

          case 't':
            if (retryname[1] == 't' && retryname[2] == 'y')
            switch (retryname[3])
              {
                error_t opentty (file_t *result)
                  {
                  error_t err;
                  error_t ctty_open (file_t port)
                    {
                      if (port == MACH_PORT_NULL)
                        return ENXIO; /* No controlling terminal.  */
                      return __termctty_open_terminal (port,
                                               flags,
                                               result);
                    }
                  err = (*use_init_port) (INIT_PORT_CTTYID, &ctty_open);
                  if (! err)
                    err = reauthenticate (*result);
                  return err;
                  }

              case '\0':
                return opentty (result);
              case '/':
                if (err = opentty (&startdir))
                  return err;
                strcpy (retryname, &retryname[4]);
                break;
              default:
                goto bad_magic;
              }
            else
            goto bad_magic;
            break;

          default:
          bad_magic:
            return EGRATUITOUS;
          }
        break;

      default:
        return EGRATUITOUS;
      }

      if (startdir != MACH_PORT_NULL)
      {
        err = lookup_op (startdir);
        __mach_port_deallocate (__mach_task_self (), startdir);
        startdir = MACH_PORT_NULL;
      }
      else
      err = (*use_init_port) (dirport, &lookup_op);
    } while (! err);

  return err;
}
weak_alias (__hurd_file_name_lookup_retry, hurd_file_name_lookup_retry)

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