/* -*- linux-c -*- --------------------------------------------------------- *
   *
   * linux/fs/devpts/inode.c
   *
   *  Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
   *
   * This file is part of the Linux kernel and is made available under
   * the terms of the GNU General Public License, version 2, or at your
   * option, any later version, incorporated herein by reference.
   *
   * ------------------------------------------------------------------------- */
  
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/fs.h>
  #include <linux/sched.h>
  #include <linux/namei.h>

  #include <linux/slab.h>

  #include <linux/mount.h>
  #include <linux/tty.h>

  #include <linux/mutex.h>

  #include <linux/magic.h>

  #include <linux/idr.h>

  #include <linux/devpts_fs.h>

  #include <linux/parser.h>

  #include <linux/fsnotify.h>

  #include <linux/seq_file.h>

  #define DEVPTS_DEFAULT_MODE 0600

  /*
   * ptmx is a new node in /dev/pts and will be unused in legacy (single-
   * instance) mode. To prevent surprises in user space, set permissions of
   * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
   * permissions.
   */
  #define DEVPTS_DEFAULT_PTMX_MODE 0000

  #define PTMX_MINOR	2

  /*
   * sysctl support for setting limits on the number of Unix98 ptys allocated.
   * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
   */
  static int pty_limit = NR_UNIX98_PTY_DEFAULT;

  static int pty_reserve = NR_UNIX98_PTY_RESERVE;

  static int pty_limit_min;

  static int pty_limit_max = INT_MAX;

  static int pty_count;
  
  static struct ctl_table pty_table[] = {
  	{
  		.procname	= "max",
  		.maxlen		= sizeof(int),
  		.mode		= 0644,
  		.data		= &pty_limit,
  		.proc_handler	= proc_dointvec_minmax,
  		.extra1		= &pty_limit_min,
  		.extra2		= &pty_limit_max,
  	}, {

  		.procname	= "reserve",
  		.maxlen		= sizeof(int),
  		.mode		= 0644,
  		.data		= &pty_reserve,
  		.proc_handler	= proc_dointvec_minmax,
  		.extra1		= &pty_limit_min,
  		.extra2		= &pty_limit_max,
  	}, {

  		.procname	= "nr",
  		.maxlen		= sizeof(int),
  		.mode		= 0444,
  		.data		= &pty_count,
  		.proc_handler	= proc_dointvec,
  	},
  	{}
  };
  
  static struct ctl_table pty_kern_table[] = {
  	{
  		.procname	= "pty",
  		.mode		= 0555,
  		.child		= pty_table,
  	},
  	{}
  };
  
  static struct ctl_table pty_root_table[] = {
  	{
  		.procname	= "kernel",
  		.mode		= 0555,
  		.child		= pty_kern_table,
  	},
  	{}
  };

  static DEFINE_MUTEX(allocated_ptys_lock);

  static struct vfsmount *devpts_mnt;

  struct pts_mount_opts {

  	int setuid;
  	int setgid;

  	kuid_t   uid;
  	kgid_t   gid;

  	umode_t mode;

  	umode_t ptmxmode;

  	int newinstance;

  	int max;

  };

  enum {

  	Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,  Opt_max,

  	Opt_err
  };

  static const match_table_t tokens = {

  	{Opt_uid, "uid=%u"},
  	{Opt_gid, "gid=%u"},
  	{Opt_mode, "mode=%o"},

  #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
  	{Opt_ptmxmode, "ptmxmode=%o"},

  	{Opt_newinstance, "newinstance"},

  	{Opt_max, "max=%d"},

  #endif

  	{Opt_err, NULL}
  };

  struct pts_fs_info {
  	struct ida allocated_ptys;

  	struct pts_mount_opts mount_opts;

  	struct dentry *ptmx_dentry;

  };
  
  static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
  {
  	return sb->s_fs_info;
  }

  static inline struct super_block *pts_sb_from_inode(struct inode *inode)
  {

  #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES

  	if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
  		return inode->i_sb;

  #endif

  	return devpts_mnt->mnt_sb;
  }

  #define PARSE_MOUNT	0
  #define PARSE_REMOUNT	1

  /*
   * parse_mount_options():
   * 	Set @opts to mount options specified in @data. If an option is not
   * 	specified in @data, set it to its default value. The exception is
   * 	'newinstance' option which can only be set/cleared on a mount (i.e.
   * 	cannot be changed during remount).
   *
   * Note: @data may be NULL (in which case all options are set to default).
   */

  static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)

  {

  	char *p;

  	kuid_t uid;
  	kgid_t gid;

  	opts->setuid  = 0;
  	opts->setgid  = 0;

  	opts->uid     = GLOBAL_ROOT_UID;
  	opts->gid     = GLOBAL_ROOT_GID;

  	opts->mode    = DEVPTS_DEFAULT_MODE;

  	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;

  	opts->max     = NR_UNIX98_PTY_MAX;

  	/* newinstance makes sense only on initial mount */
  	if (op == PARSE_MOUNT)
  		opts->newinstance = 0;

  	while ((p = strsep(&data, ",")) != NULL) {
  		substring_t args[MAX_OPT_ARGS];
  		int token;
  		int option;
  
  		if (!*p)

  			continue;

  
  		token = match_token(p, tokens, args);
  		switch (token) {
  		case Opt_uid:
  			if (match_int(&args[0], &option))
  				return -EINVAL;

  			uid = make_kuid(current_user_ns(), option);
  			if (!uid_valid(uid))
  				return -EINVAL;
  			opts->uid = uid;

  			opts->setuid = 1;

  			break;
  		case Opt_gid:
  			if (match_int(&args[0], &option))
  				return -EINVAL;

  			gid = make_kgid(current_user_ns(), option);
  			if (!gid_valid(gid))
  				return -EINVAL;
  			opts->gid = gid;

  			opts->setgid = 1;

  			break;
  		case Opt_mode:
  			if (match_octal(&args[0], &option))
  				return -EINVAL;

  			opts->mode = option & S_IALLUGO;

  			break;

  #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
  		case Opt_ptmxmode:
  			if (match_octal(&args[0], &option))
  				return -EINVAL;
  			opts->ptmxmode = option & S_IALLUGO;
  			break;

  		case Opt_newinstance:
  			/* newinstance makes sense only on initial mount */
  			if (op == PARSE_MOUNT)
  				opts->newinstance = 1;
  			break;

  		case Opt_max:
  			if (match_int(&args[0], &option) ||
  			    option < 0 || option > NR_UNIX98_PTY_MAX)
  				return -EINVAL;
  			opts->max = option;
  			break;

  #endif

  		default:
  			printk(KERN_ERR "devpts: called with bogus options
  ");

  			return -EINVAL;
  		}
  	}

  
  	return 0;
  }

  #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
  static int mknod_ptmx(struct super_block *sb)
  {
  	int mode;
  	int rc = -ENOMEM;
  	struct dentry *dentry;
  	struct inode *inode;
  	struct dentry *root = sb->s_root;
  	struct pts_fs_info *fsi = DEVPTS_SB(sb);
  	struct pts_mount_opts *opts = &fsi->mount_opts;

  	kuid_t root_uid;
  	kgid_t root_gid;
  
  	root_uid = make_kuid(current_user_ns(), 0);
  	root_gid = make_kgid(current_user_ns(), 0);
  	if (!uid_valid(root_uid) || !gid_valid(root_gid))
  		return -EINVAL;

  
  	mutex_lock(&root->d_inode->i_mutex);
  
  	/* If we have already created ptmx node, return */
  	if (fsi->ptmx_dentry) {
  		rc = 0;
  		goto out;
  	}
  
  	dentry = d_alloc_name(root, "ptmx");
  	if (!dentry) {
  		printk(KERN_NOTICE "Unable to alloc dentry for ptmx node
  ");
  		goto out;
  	}
  
  	/*
  	 * Create a new 'ptmx' node in this mount of devpts.
  	 */
  	inode = new_inode(sb);
  	if (!inode) {
  		printk(KERN_ERR "Unable to alloc inode for ptmx node
  ");
  		dput(dentry);
  		goto out;
  	}
  
  	inode->i_ino = 2;

  	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
  
  	mode = S_IFCHR|opts->ptmxmode;
  	init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));

  	inode->i_uid = root_uid;
  	inode->i_gid = root_gid;

  
  	d_add(dentry, inode);
  
  	fsi->ptmx_dentry = dentry;
  	rc = 0;

  out:
  	mutex_unlock(&root->d_inode->i_mutex);
  	return rc;
  }
  
  static void update_ptmx_mode(struct pts_fs_info *fsi)
  {
  	struct inode *inode;
  	if (fsi->ptmx_dentry) {
  		inode = fsi->ptmx_dentry->d_inode;
  		inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
  	}
  }
  #else
  static inline void update_ptmx_mode(struct pts_fs_info *fsi)
  {
         return;
  }
  #endif

  static int devpts_remount(struct super_block *sb, int *flags, char *data)
  {

  	int err;

  	struct pts_fs_info *fsi = DEVPTS_SB(sb);
  	struct pts_mount_opts *opts = &fsi->mount_opts;

  	sync_filesystem(sb);

  	err = parse_mount_options(data, PARSE_REMOUNT, opts);

  
  	/*
  	 * parse_mount_options() restores options to default values
  	 * before parsing and may have changed ptmxmode. So, update the
  	 * mode in the inode too. Bogus options don't fail the remount,
  	 * so do this even on error return.
  	 */
  	update_ptmx_mode(fsi);
  
  	return err;

  }

  static int devpts_show_options(struct seq_file *seq, struct dentry *root)

  {

  	struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);

  	struct pts_mount_opts *opts = &fsi->mount_opts;
  
  	if (opts->setuid)

  		seq_printf(seq, ",uid=%u", from_kuid_munged(&init_user_ns, opts->uid));

  	if (opts->setgid)

  		seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, opts->gid));

  	seq_printf(seq, ",mode=%03o", opts->mode);

  #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
  	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);

  	if (opts->max < NR_UNIX98_PTY_MAX)
  		seq_printf(seq, ",max=%d", opts->max);

  #endif

  
  	return 0;
  }

  static const struct super_operations devpts_sops = {

  	.statfs		= simple_statfs,
  	.remount_fs	= devpts_remount,

  	.show_options	= devpts_show_options,

  };

  static void *new_pts_fs_info(void)
  {
  	struct pts_fs_info *fsi;
  
  	fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
  	if (!fsi)
  		return NULL;
  
  	ida_init(&fsi->allocated_ptys);

  	fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;

  	fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;

  
  	return fsi;
  }

  static int
  devpts_fill_super(struct super_block *s, void *data, int silent)
  {

  	struct inode *inode;

  
  	s->s_blocksize = 1024;
  	s->s_blocksize_bits = 10;
  	s->s_magic = DEVPTS_SUPER_MAGIC;
  	s->s_op = &devpts_sops;

  	s->s_time_gran = 1;

  	s->s_fs_info = new_pts_fs_info();
  	if (!s->s_fs_info)
  		goto fail;

  	inode = new_inode(s);
  	if (!inode)

  		goto fail;

  	inode->i_ino = 1;
  	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;

  	inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
  	inode->i_op = &simple_dir_inode_operations;
  	inode->i_fop = &simple_dir_operations;

  	set_nlink(inode, 2);

  	s->s_root = d_make_root(inode);

  	if (s->s_root)
  		return 0;

  	printk(KERN_ERR "devpts: get root dentry failed
  ");

  fail:
  	return -ENOMEM;
  }

  #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES

  static int compare_init_pts_sb(struct super_block *s, void *p)
  {
  	if (devpts_mnt)
  		return devpts_mnt->mnt_sb == s;

  	return 0;
  }

  /*

   * devpts_mount()

   *
   *     If the '-o newinstance' mount option was specified, mount a new
   *     (private) instance of devpts.  PTYs created in this instance are
   *     independent of the PTYs in other devpts instances.
   *
   *     If the '-o newinstance' option was not specified, mount/remount the
   *     initial kernel mount of devpts.  This type of mount gives the
   *     legacy, single-instance semantics.

   *

   *     The 'newinstance' option is needed to support multiple namespace
   *     semantics in devpts while preserving backward compatibility of the
   *     current 'single-namespace' semantics. i.e all mounts of devpts
   *     without the 'newinstance' mount option should bind to the initial

   *     kernel mount, like mount_single().

   *

   *     Mounts with 'newinstance' option create a new, private namespace.

   *

   *     NOTE:

   *

   *     For single-mount semantics, devpts cannot use mount_single(),
   *     because mount_single()/sget() find and use the super-block from

   *     the most recent mount of devpts. But that recent mount may be a

   *     'newinstance' mount and mount_single() would pick the newinstance

   *     super-block instead of the initial super-block.

   */

  static struct dentry *devpts_mount(struct file_system_type *fs_type,
  	int flags, const char *dev_name, void *data)

  {

  	int error;
  	struct pts_mount_opts opts;

  	struct super_block *s;

  	error = parse_mount_options(data, PARSE_MOUNT, &opts);
  	if (error)

  		return ERR_PTR(error);

  	/* Require newinstance for all user namespace mounts to ensure
  	 * the mount options are not changed.
  	 */
  	if ((current_user_ns() != &init_user_ns) && !opts.newinstance)
  		return ERR_PTR(-EINVAL);

  	if (opts.newinstance)

  		s = sget(fs_type, NULL, set_anon_super, flags, NULL);

  	else

  		s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
  			 NULL);

  	if (IS_ERR(s))

  		return ERR_CAST(s);

  
  	if (!s->s_root) {

  		error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
  		if (error)
  			goto out_undo_sget;
  		s->s_flags |= MS_ACTIVE;
  	}

  	memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));

  	error = mknod_ptmx(s);

  	if (error)

  		goto out_undo_sget;

  	return dget(s->s_root);

  
  out_undo_sget:

  	deactivate_locked_super(s);

  	return ERR_PTR(error);

  }

  #else
  /*
   * This supports only the legacy single-instance semantics (no
   * multiple-instance semantics)
   */

  static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
  		const char *dev_name, void *data)

  {

  	return mount_single(fs_type, flags, data, devpts_fill_super);

  }
  #endif

  static void devpts_kill_sb(struct super_block *sb)
  {
  	struct pts_fs_info *fsi = DEVPTS_SB(sb);

  	ida_destroy(&fsi->allocated_ptys);

  	kfree(fsi);

  	kill_litter_super(sb);

  }

  static struct file_system_type devpts_fs_type = {

  	.name		= "devpts",

  	.mount		= devpts_mount,

  	.kill_sb	= devpts_kill_sb,

  #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
  	.fs_flags	= FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT,
  #endif

  };
  
  /*
   * The normal naming convention is simply /dev/pts/<number>; this conforms
   * to the System V naming convention
   */

  int devpts_new_index(struct inode *ptmx_inode)

  {

  	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
  	struct pts_fs_info *fsi = DEVPTS_SB(sb);

  	int index;

  	int ida_ret;

  
  retry:

  	if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))

  		return -ENOMEM;

  
  	mutex_lock(&allocated_ptys_lock);

  	if (pty_count >= pty_limit -
  			(fsi->mount_opts.newinstance ? pty_reserve : 0)) {
  		mutex_unlock(&allocated_ptys_lock);
  		return -ENOSPC;
  	}

  	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);

  	if (ida_ret < 0) {

  		mutex_unlock(&allocated_ptys_lock);

  		if (ida_ret == -EAGAIN)

  			goto retry;
  		return -EIO;
  	}

  	if (index >= fsi->mount_opts.max) {

  		ida_remove(&fsi->allocated_ptys, index);

  		mutex_unlock(&allocated_ptys_lock);

  		return -ENOSPC;

  	}

  	pty_count++;

  	mutex_unlock(&allocated_ptys_lock);
  	return index;
  }

  void devpts_kill_index(struct inode *ptmx_inode, int idx)

  {

  	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
  	struct pts_fs_info *fsi = DEVPTS_SB(sb);

  	mutex_lock(&allocated_ptys_lock);

  	ida_remove(&fsi->allocated_ptys, idx);

  	pty_count--;

  	mutex_unlock(&allocated_ptys_lock);
  }

  /**
   * devpts_pty_new -- create a new inode in /dev/pts/
   * @ptmx_inode: inode of the master
   * @device: major+minor of the node to be created
   * @index: used as a name of the node
   * @priv: what's given back by devpts_get_priv
   *
   * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
   */

  struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
  		void *priv)

  {

  	struct dentry *dentry;

  	struct super_block *sb = pts_sb_from_inode(ptmx_inode);

  	struct inode *inode;

  	struct dentry *root = sb->s_root;

  	struct pts_fs_info *fsi = DEVPTS_SB(sb);
  	struct pts_mount_opts *opts = &fsi->mount_opts;

  	char s[12];

  	inode = new_inode(sb);

  	if (!inode)

  		return ERR_PTR(-ENOMEM);

  	inode->i_ino = index + 3;

  	inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
  	inode->i_gid = opts->setgid ? opts->gid : current_fsgid();

  	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;

  	init_special_inode(inode, S_IFCHR|opts->mode, device);

  	inode->i_private = priv;

  	sprintf(s, "%d", index);

  	mutex_lock(&root->d_inode->i_mutex);

  	dentry = d_alloc_name(root, s);

  	if (dentry) {

  		d_add(dentry, inode);

  		fsnotify_create(root->d_inode, dentry);

  	} else {
  		iput(inode);

  		inode = ERR_PTR(-ENOMEM);

  	}

  	mutex_unlock(&root->d_inode->i_mutex);

  	return inode;

  }

  /**
   * devpts_get_priv -- get private data for a slave
   * @pts_inode: inode of the slave
   *
   * Returns whatever was passed as priv in devpts_pty_new for a given inode.
   */

  void *devpts_get_priv(struct inode *pts_inode)

  {

  	struct dentry *dentry;

  	void *priv = NULL;

  	BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));

  	/* Ensure dentry has not been deleted by devpts_pty_kill() */
  	dentry = d_find_alias(pts_inode);
  	if (!dentry)
  		return NULL;

  	if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)

  		priv = pts_inode->i_private;

  
  	dput(dentry);

  	return priv;

  }

  /**
   * devpts_pty_kill -- remove inode form /dev/pts/
   * @inode: inode of the slave to be removed
   *
   * This is an inverse operation of devpts_pty_new.
   */

  void devpts_pty_kill(struct inode *inode)

  {

  	struct super_block *sb = pts_sb_from_inode(inode);
  	struct dentry *root = sb->s_root;

  	struct dentry *dentry;

  	BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));

  	mutex_lock(&root->d_inode->i_mutex);

  
  	dentry = d_find_alias(inode);

  	drop_nlink(inode);

  	d_delete(dentry);
  	dput(dentry);	/* d_alloc_name() in devpts_pty_new() */

  	dput(dentry);		/* d_find_alias above */

  	mutex_unlock(&root->d_inode->i_mutex);

  }
  
  static int __init init_devpts_fs(void)
  {
  	int err = register_filesystem(&devpts_fs_type);

  	struct ctl_table_header *table;

  	if (!err) {

  		table = register_sysctl_table(pty_root_table);

  		devpts_mnt = kern_mount(&devpts_fs_type);

  		if (IS_ERR(devpts_mnt)) {

  			err = PTR_ERR(devpts_mnt);

  			unregister_filesystem(&devpts_fs_type);

  			unregister_sysctl_table(table);

  		}

  	}
  	return err;
  }

  module_init(init_devpts_fs)