/* hairy bits of Hurd file name lookup

   Copyright (C) 1992-2018 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, see

   <http://www.gnu.org/licenses/>.  */

#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 <_itoa.h>

#include <eloop-threshold.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, const 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)

    {

      if (file_name[0] == '/' && file_name[1] != '\0')

	{

	  while (file_name[1] == '/')

	    /* Remove double leading slash.  */

	    file_name++;

	  if (file_name[1] != '\0')

	    /* Remove leading slash when we have more than the slash.  */

	    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++ >= __eloop_threshold ())

	    {

	      __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 only, 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)

		    {

		      if (flags & O_DIRECTORY && !S_ISDIR (st.st_mode))

			err = ENOTDIR;

		      if (S_ISLNK (st.st_mode))

			err = ELOOP;

		      else if (st.st_mode & (S_IPTRANS|S_IATRANS))

			{

			  if (st.st_uid != 0)

			    err = ELOOP;

			  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 = ELOOP;

			    }

			}

		    }

		}

	      /* 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++ >= __eloop_threshold ())

		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_internal (&retryname[3], &end, 10, 0);

		  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)