path: root/trans/mtab.c

/* This is an mtab translator.

   Copyright (C) 2013 Free Software Foundation, Inc.

   Written by Justus Winter <4winter@informatik.uni-hamburg.de>

   This file is part of the GNU Hurd.

   The GNU Hurd is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2, or (at
   your option) any later version.

   The GNU Hurd 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
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with the GNU Hurd.  If not, see <http://www.gnu.org/licenses/>.  */

#include <argp.h>
#include <argz.h>
#include <error.h>
#include <fcntl.h>
#include <hurd.h>
#include <hurd/trivfs.h>
#include <inttypes.h>
#include <mntent.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>
#include <version.h>

#include "fsys_U.h"

static char *target_path = NULL;
static int insecure = 0;

/* Our control port.  */
struct trivfs_control *control;

/* These kind of objects are created and populated in the open_hook.
   They keep track of the content and file position of the client.  */
struct mtab
{
  char *contents;
  size_t contents_len;
  off_t offs;
};

const char *argp_program_version = STANDARD_HURD_VERSION (mtab);

static const struct argp_option options[] =
{
  {"insecure", 'I', 0, 0,
   "Follow translators not bound to nodes owned by you or root"},
  {}
};

/* Parse a command line option.	 */
error_t parse_opt (int key, char *arg, struct argp_state *state)
{
  switch (key)
    {
    case 'I':
      insecure = 1;
      break;

    case ARGP_KEY_ARG:
      target_path = realpath (arg, NULL);
      if (! target_path)
	argp_error (state, "Error while canonicalizing path");
      break;

    case ARGP_KEY_NO_ARGS:
      argp_usage (state);
      return EINVAL;

    default:
      return ARGP_ERR_UNKNOWN;
    }
  return 0;
}

static struct argp argp =
  {
    options,
    parse_opt,
    "TARGET\tFile name of a node with an active translator",
    "A translator providing mtab compatible information about active "
    "and passive translators below TARGET.",
  };

/* This will be called from libtrivfs to help construct the answer
   to an fsys_get_options RPC.	*/
error_t
trivfs_append_args (struct trivfs_control *fsys,
		    char **argz, size_t *argz_len)
{
  error_t err;

  if (insecure)
    {
      err = argz_add (argz, argz_len, target_path);
      if (err)
	return err;
    }

  err = argz_add (argz, argz_len, target_path);
  return err;
}

/* Setting this variable makes libtrivfs use our argp to
   parse options passed in an fsys_set_options RPC.  */
struct argp *trivfs_runtime_argp = &argp;

/* Authentication of the current process.  */
uid_t *uids;
gid_t *gids;
size_t uids_len, gids_len;

/* Initialize and populate the uids and gids vectors.  */
error_t
get_credentials (void)
{
  /* Fetch uids...  */
  uids_len = geteuids (0, 0);
  if (uids_len < 0)
    return errno;

  uids = malloc (uids_len * sizeof (uid_t));
  if (! uids)
    return ENOMEM;

  uids_len = geteuids (uids_len, uids);
  if (uids_len < 0)
    return errno;

  /* ... and gids.  */
  gids_len = getgroups (0, 0);
  if (gids_len < 0)
    return errno;

  gids = malloc (gids_len * sizeof (gid_t));
  if (! uids)
    return ENOMEM;

  gids_len = getgroups (gids_len, gids);
  if (gids_len < 0)
    return errno;

  return 0;
}

/* Check if the given struct stat describes a node owned by the
   current user.  */
int
is_owner (io_statbuf_t *st)
{
  int found = 0;
  for (size_t i = 0; i < uids_len; i++)
    if (uids[i] == st->st_uid)
      {
	found = 1;
	break;
      }

  if (! found)
    return 0;

  found = 0;
  for (size_t i = 0; i < gids_len; i++)
    if (gids[i] == st->st_gid)
      {
	found = 1;
	break;
      }

  return found;
}

error_t
mtab_populate (struct mtab *mtab, const char *path, int insecure);

error_t
argz_add_device (char **options, size_t *options_len, const char *device);

error_t
map_device_to_path (const char *device, char **path);

int
main (int argc, char *argv[])
{
  error_t err;

  err = argp_parse (&argp, argc, argv, ARGP_IN_ORDER, 0, 0);
  if (err)
    error (1, err, "argument parsing");

  err = get_credentials ();
  if (err)
    error (2, err, "getting credentials");

  mach_port_t bootstrap;
  task_get_bootstrap_port (mach_task_self (), &bootstrap);
  if (bootstrap != MACH_PORT_NULL)
    {
      /* Started as a translator.  */

      auth_t nullauth;
      err = auth_makeauth (getauth (),
			   NULL, MACH_MSG_TYPE_COPY_SEND, 0,
			   NULL, 0,
			   NULL, 0,
			   NULL, 0,
			   NULL, 0,
			   &nullauth);
      if (err)
        error (3, err, "dropping credentials");

      err = setauth (nullauth);
      if (err)
        error (3, err, "dropping credentials");

      /* Reply to our parent.  */
      err = trivfs_startup (bootstrap, 0, 0, 0, 0, 0, &control);
      mach_port_deallocate (mach_task_self (), bootstrap);
      if (err)
	error (4, err, "trivfs_startup");

      /* Launch.  */
      ports_manage_port_operations_one_thread (control->pi.bucket,
					       trivfs_demuxer,
					       0);
    }
  else
    {
      /* One-shot mode.	 */
      struct mtab mtab = { NULL, 0, 0 };
      err = mtab_populate (&mtab, target_path, insecure);
      if (err)
	error (5, err, "%s", target_path);

      if (mtab.contents)
	printf ("%s", mtab.contents);
    }

  return 0;
}

error_t
mtab_add_entry (struct mtab *mtab, const char *entry, size_t length)
{
  char *p = realloc (mtab->contents, mtab->contents_len + length + 1);
  if (! p)
    return ENOMEM;

  memcpy (&p[mtab->contents_len], entry, length);

  mtab->contents = p;
  mtab->contents_len += length;

  /* Zero-terminate contents so that we can also interpret it as
     string.  */
  mtab->contents[mtab->contents_len] = '\0';

  return 0;
}

/* Populates the given MTAB object with the information for PATH.  If
   INSECURE is given, also follow translators bound to nodes not owned
   by root or the current user.  */
/* XXX split up */
error_t
mtab_populate (struct mtab *mtab, const char *path, int insecure)
{
  error_t err = 0;

  /* These resources are freed in the epilogue.	 */
  file_t node = MACH_PORT_NULL;
  fsys_t fsys = MACH_PORT_NULL;
  char *argz = NULL;
  size_t argz_len = 0;
  char **argv = NULL;
  char *type = NULL;
  char *options = NULL;
  size_t options_len = 0;
  char *src = NULL;
  char *entry = NULL;
  size_t entry_len = 0;
  char *children = NULL;
  size_t children_len = 0;

  /* Get the underlying node.  */
  node = file_name_lookup (path, O_NOTRANS, 0666);
  if (node == MACH_PORT_NULL)
    {
      err = errno;
      goto errout;
    }

  if (! insecure)
    {
      /* Check who owns the node the translator is bound to.  */
      io_statbuf_t st;
      err = io_stat (node, &st);
      if (err)
	goto errout;

      if (st.st_uid != 0 && st.st_gid != 0 && ! is_owner (&st))
	{
	  err = EPERM;
	  goto errout;
	}
    }

  err = file_get_translator_cntl (node, &fsys);
  if (err == EPERM)
    /* If we do not have permission to do that, it cannot be a node
       bound to our control port, so ignore this error.	 */
    err = 0;

  if (err == ENXIO && strcmp (path, "/") == 0)
    /* The root translator fails differently, but this can't be bound
       to our control port either, so ignore this error.  */
    err = 0;

  if (err)
    return err;

  if (control && control->pi.port_right == fsys)
    /* This node is bound to our control port, ignore it.  */
    goto errout;

  /* Re-do the lookup without O_NOTRANS to get the root node.  */
  mach_port_deallocate (mach_task_self (), node);
  node = file_name_lookup (path, 0, 0666);
  if (node == MACH_PORT_NULL)
    {
      err = errno;
      goto errout;
    }

  /* Query its options.	 */
  err = file_get_fs_options (node, &argz, &argz_len);
  if (err)
    {
      if (err == EOPNOTSUPP)
	err = 0; /* There's not much we could do then.	*/

      goto errout;
    }

  size_t count = argz_count (argz, argz_len);
  argv = malloc ((count + 1) * sizeof (char *));
  if (! argv)
    {
      err = ENOMEM;
      goto errout;
    }

  argz_extract (argz, argz_len, argv);

  type = strdup (argv[0]);
  if (! type)
    {
      err = ENOMEM;
      goto errout;
    }

  for (int i = 1; i < count - 1; i++)
    {
      char *v = argv[i];

      if (*v == '-')
	v++;
      if (*v == '-')
	v++;

      err = argz_add (&options, &options_len, v);
      if (err)
	goto errout;
    }

  err = argz_add_device (&options, &options_len, argv[count - 1]);
  if (err)
    goto errout;

  argz_stringify (options, options_len, ',');

  string_t source;
  err = fsys_get_source (node, source);
  if (err)
    {
      if (err == EOPNOTSUPP)
	{
	  /* Guess based on the last argument.	*/
	  err = map_device_to_path (argv[count - 1], &src);
	  if (err)
	    goto errout;
	}
      else
	goto errout;
    }
  else
    src = source;

  entry_len = asprintf (&entry, "%s %s %s %s 0 0\n", src, path, type,
			options? options: MNTOPT_DEFAULTS);
  if (! entry)
    {
      err = ENOMEM;
      goto errout;
    }

  err = mtab_add_entry (mtab, entry, entry_len);
  if (err)
    goto errout;

  /* path has an active translator, query its children.	 */
  err = fsys_get_children (node, &children, &children_len);
  if (err == EOPNOTSUPP)
    {
      err = 0;
      children_len = 0;
    }

  if (err)
    goto errout;

  if (children_len)
    for (char *c = children; c; c = argz_next (children, children_len, c))
      {
	char *p = NULL;
	asprintf (&p, "%s%s%s",
		  path,
		  path[strlen (path) - 1] == '/'? "": "/",
		  c);
	if (! p)
	  {
	    err = ENOMEM;
	    goto errout;
	  }

	err = mtab_populate (mtab, p, insecure);
	if (err)
	  {
	    /* There is really not much we can do about errors here.  */
	    error (0, err, "%s", p);
	    err = 0;
	  }

	free (p);
      }

 errout:
  if (node != MACH_PORT_NULL)
    mach_port_deallocate (mach_task_self (), node);

  if (fsys != MACH_PORT_NULL)
    mach_port_deallocate (mach_task_self (), fsys);

  if (argz)
    vm_deallocate (mach_task_self (), (vm_address_t) argz, argz_len);

  free (argv);
  free (type);
  free (options);

  if (src != source)
    free (src);

  free (entry);

  if (children)
    vm_deallocate (mach_task_self (), (vm_address_t) children, children_len);

  return err;
}

/* Decodes the DEVICE string into appropriate OPTIONS.  Currently only
   tmpfs-style size declarations are supported.  */
error_t
argz_add_device (char **options, size_t *options_len, const char *device)
{
  error_t err;
  char *end = NULL;
  intmax_t size = strtoimax (device, &end, 0);
  if (end == NULL || end == device)
    return 0;

  if (size < 0)
    return 0;

  switch (*end)
    {
      case 'g':
      case 'G':
      case 'm':
      case 'M':
      case 'k':
      case 'K':
	break;
    default:
      return 0;
    }

  /* device specifies a size.  */
  char *arg = NULL;
  asprintf (&arg, "size=%s", device);
  if (! arg)
    return ENOMEM;

  err = argz_add (options, options_len, arg);

  free (arg);
  return err;
}

/* Matches [hs]d\ds\d\d?.  */
int
looks_like_block_device (const char *s)
{
  size_t len = strlen (s);
  if (len != 3 && len != 5 && len != 6)
    return 0;

  return ((s[0] == 'h' || s[0] == 's') && s[1] == 'd' && isdigit (s[2]) &&
          (len == 3 || (s[3] == 's' && isdigit (s[4]) &&
                        (len == 5 || isdigit (s[5])))));
}

/* Map a device string to a file name referencing the appropriate
   device file.	 */
error_t
map_device_to_path (const char *device, char **path)
{
  if (strncmp (device, "device:", 7) == 0)
    asprintf (path, "/dev/%s", &device[7]);
  else if (strncmp (device, "/dev/", 5) == 0)
    *path = strdup (device);
  else if (looks_like_block_device (device))
    asprintf (path, "/dev/%s", device);
  else
    *path = strdup ("none");

  if (! *path)
    return ENOMEM;

  return 0;
}

/* Trivfs hooks.  */
int trivfs_fstype = FSTYPE_MISC;
int trivfs_fsid = 0;

int trivfs_allow_open = O_READ;

int trivfs_support_read = 1;
int trivfs_support_write = 0;
int trivfs_support_exec = 0;

void
trivfs_modify_stat (struct trivfs_protid *cred, struct stat *st)
{
  /* Mark the node as a read-only plain file.  */
  st->st_mode &= ~(S_IFMT | ALLPERMS);
  st->st_mode |= (S_IFREG | S_IRUSR | S_IRGRP | S_IROTH);
  st->st_size = ((struct mtab *) cred->po->hook)->contents_len;
}

error_t
trivfs_goaway (struct trivfs_control *cntl, int flags)
{
  exit (EXIT_SUCCESS);
}

static error_t
open_hook (struct trivfs_peropen *peropen)
{
  struct mtab *mtab = malloc (sizeof (struct mtab));
  if (mtab == NULL)
    return ENOMEM;

  /* Hook! */
  peropen->hook = mtab;

  /* Initialize the fields.  */
  mtab->offs = 0;
  mtab->contents = NULL;
  mtab->contents_len = 0;

  return mtab_populate (mtab, target_path, insecure);
}

static void
close_hook (struct trivfs_peropen *peropen)
{
  free (((struct mtab *) peropen->hook)->contents);
  free (peropen->hook);
}

/* Read data from an IO object.	 If offset is -1, read from the object
   maintained file pointer.  If the object is not seekable, offset is
   ignored.  The amount desired to be read is in AMOUNT.  */
error_t
trivfs_S_io_read (struct trivfs_protid *cred,
		  mach_port_t reply, mach_msg_type_name_t reply_type,
		  char **data, mach_msg_type_number_t *data_len,
		  loff_t offs, mach_msg_type_number_t amount)
{
  struct mtab *op;

  /* Deny access if they have bad credentials.	*/
  if (! cred)
    return EOPNOTSUPP;

  if (! (cred->po->openmodes & O_READ))
    return EBADF;

  /* Get the offset.  */
  op = cred->po->hook;
  if (offs == -1)
    offs = op->offs;

  /* Prune the amount they want to read.  */
  if (offs > op->contents_len)
    offs = op->contents_len;
  if (offs + amount > op->contents_len)
    amount = op->contents_len - offs;

  if (amount > 0)
    {
      /* Possibly allocate a new buffer.  */
      if (*data_len < amount)
	{
	  *data = mmap (0, amount, PROT_READ|PROT_WRITE, MAP_ANON, 0, 0);
	  if (*data == MAP_FAILED)
	    return ENOMEM;
	}

      /* Copy the constant data into the buffer.  */
      memcpy ((char *) *data, op->contents + offs, amount);

      /* Update the saved offset.  */
      op->offs += amount;
    }

  *data_len = amount;
  return 0;
}


/* Change current read/write offset */
error_t
trivfs_S_io_seek (struct trivfs_protid *cred,
		  mach_port_t reply, mach_msg_type_name_t reply_type,
		  off_t offs, int whence, off_t *new_offs)
{
  if (! cred)
    return EOPNOTSUPP;

  struct mtab *op = cred->po->hook;

  switch (whence)
    {
    case SEEK_CUR:
      offs += op->offs;
      goto check;
    case SEEK_END:
      offs += op->contents_len;
    case SEEK_SET:
    check:
      if (offs >= 0)
	{
	  *new_offs = op->offs = offs;
	  break;
	}
    default:
      return EINVAL;
    }

  return 0;
}

/* If this variable is set, it is called every time a new peropen
   structure is created and initialized.  */
error_t (*trivfs_peropen_create_hook)(struct trivfs_peropen *) = open_hook;

/* If this variable is set, it is called every time a peropen structure
   is about to be destroyed.  */
void (*trivfs_peropen_destroy_hook) (struct trivfs_peropen *) = close_hook;

/* Tell how much data can be read from the object without blocking for
   a "long time" (this should be the same meaning of "long time" used
   by the nonblocking flag.  */
kern_return_t
trivfs_S_io_readable (struct trivfs_protid *cred,
		      mach_port_t reply, mach_msg_type_name_t replytype,
		      mach_msg_type_number_t *amount)
{
  if (!cred)
    return EOPNOTSUPP;

  if (!(cred->po->openmodes & O_READ))
    return EINVAL;

  struct mtab *op = cred->po->hook;

  *amount = op->contents_len - op->offs;
  return 0;
}

/* SELECT_TYPE is the bitwise OR of SELECT_READ, SELECT_WRITE, and SELECT_URG.
   Block until one of the indicated types of i/o can be done "quickly", and
   return the types that are then available.  ID_TAG is returned as passed; it
   is just for the convenience of the user in matching up reply messages with
   specific requests sent.  */
kern_return_t
trivfs_S_io_select (struct trivfs_protid *cred,
		    mach_port_t reply, mach_msg_type_name_t replytype,
		    int *type)
{
  if (!cred)
    return EOPNOTSUPP;

  if (((*type & SELECT_READ) && !(cred->po->openmodes & O_READ))
      || ((*type & SELECT_WRITE) && !(cred->po->openmodes & O_WRITE)))
    return EBADF;

  *type &= ~SELECT_URG;
  return 0;
}

kern_return_t
trivfs_S_io_select_timeout (struct trivfs_protid *cred,
			    mach_port_t reply, mach_msg_type_name_t replytype,
			    struct timespec ts,
			    int *type)
{
  return trivfs_S_io_select (cred, reply, replytype, type);
}

/* These four routines modify the O_APPEND, O_ASYNC, O_FSYNC, and
   O_NONBLOCK bits for the IO object. In addition, io_get_openmodes
   will tell you which of O_READ, O_WRITE, and O_EXEC the object can
   be used for.	 The O_ASYNC bit affects icky async I/O; good async
   I/O is done through io_async which is orthogonal to these calls. */

kern_return_t
trivfs_S_io_get_openmodes (struct trivfs_protid *cred,
			   mach_port_t reply, mach_msg_type_name_t replytype,
			   int *bits)
{
  if (!cred)
    return EOPNOTSUPP;

  *bits = cred->po->openmodes;
  return 0;
}

error_t
trivfs_S_io_set_all_openmodes(struct trivfs_protid *cred,
			      mach_port_t reply,
			      mach_msg_type_name_t replytype,
			      int mode)
{
  if (!cred)
    return EOPNOTSUPP;

  return 0;
}

kern_return_t
trivfs_S_io_set_some_openmodes (struct trivfs_protid *cred,
				mach_port_t reply,
				mach_msg_type_name_t replytype,
				int bits)
{
  if (!cred)
    return EOPNOTSUPP;

  return 0;
}

kern_return_t
trivfs_S_io_clear_some_openmodes (struct trivfs_protid *cred,
				  mach_port_t reply,
				  mach_msg_type_name_t replytype,
				  int bits)
{
  if (!cred)
    return EOPNOTSUPP;

  return 0;
}