text: // SPDX-License-Identifier: GPL-2.0-or-later
  /* AFS dynamic root handling
   *
   * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   */
  
  #include <linux/fs.h>
  #include <linux/namei.h>
  #include <linux/dns_resolver.h>
  #include "internal.h"
  
  static atomic_t afs_autocell_ino;
  
  /*
   * iget5() comparator for inode created by autocell operations
   *
   * These pseudo inodes don't match anything.
   */
  static int afs_iget5_pseudo_test(struct inode *inode, void *opaque)
  {
  	return 0;
  }
  
  /*
   * iget5() inode initialiser
   */
  static int afs_iget5_pseudo_set(struct inode *inode, void *opaque)
  {
  	struct afs_super_info *as = AFS_FS_S(inode->i_sb);
  	struct afs_vnode *vnode = AFS_FS_I(inode);
  	struct afs_fid *fid = opaque;
  
  	vnode->volume		= as->volume;
  	vnode->fid		= *fid;
  	inode->i_ino		= fid->vnode;
  	inode->i_generation	= fid->unique;
  	return 0;
  }
  
  /*
   * Create an inode for a dynamic root directory or an autocell dynamic
   * automount dir.
   */
  struct inode *afs_iget_pseudo_dir(struct super_block *sb, bool root)
  {
  	struct afs_super_info *as = AFS_FS_S(sb);
  	struct afs_vnode *vnode;
  	struct inode *inode;
  	struct afs_fid fid = {};
  
  	_enter("");
  
  	if (as->volume)
  		fid.vid = as->volume->vid;
  	if (root) {
  		fid.vnode = 1;
  		fid.unique = 1;
  	} else {
  		fid.vnode = atomic_inc_return(&afs_autocell_ino);
  		fid.unique = 0;
  	}
  
  	inode = iget5_locked(sb, fid.vnode,
  			     afs_iget5_pseudo_test, afs_iget5_pseudo_set, &fid);
  	if (!inode) {
  		_leave(" = -ENOMEM");
  		return ERR_PTR(-ENOMEM);
  	}
  
  	_debug("GOT INODE %p { ino=%lu, vl=%llx, vn=%llx, u=%x }",
  	       inode, inode->i_ino, fid.vid, fid.vnode, fid.unique);
  
  	vnode = AFS_FS_I(inode);
  
  	/* there shouldn't be an existing inode */
  	BUG_ON(!(inode->i_state & I_NEW));
  
  	inode->i_size		= 0;
  	inode->i_mode		= S_IFDIR | S_IRUGO | S_IXUGO;
  	if (root) {
  		inode->i_op	= &afs_dynroot_inode_operations;
  		inode->i_fop	= &simple_dir_operations;
  	} else {
  		inode->i_op	= &afs_autocell_inode_operations;
  	}
  	set_nlink(inode, 2);
  	inode->i_uid		= GLOBAL_ROOT_UID;
  	inode->i_gid		= GLOBAL_ROOT_GID;
  	inode->i_ctime = inode->i_atime = inode->i_mtime = current_time(inode);
  	inode->i_blocks		= 0;
  	inode->i_generation	= 0;
  
  	set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
  	if (!root) {
  		set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);
  		inode->i_flags |= S_AUTOMOUNT;
  	}
  
  	inode->i_flags |= S_NOATIME;
  	unlock_new_inode(inode);
  	_leave(" = %p", inode);
  	return inode;
  }
  
  /*
   * Probe to see if a cell may exist.  This prevents positive dentries from
   * being created unnecessarily.
   */
  static int afs_probe_cell_name(struct dentry *dentry)
  {
  	struct afs_cell *cell;
  	struct afs_net *net = afs_d2net(dentry);
  	const char *name = dentry->d_name.name;
  	size_t len = dentry->d_name.len;
  	int ret;
  
  	/* Names prefixed with a dot are R/W mounts. */
  	if (name[0] == '.') {
  		if (len == 1)
  			return -EINVAL;
  		name++;
  		len--;
  	}
  
  	cell = afs_lookup_cell_rcu(net, name, len);
  	if (!IS_ERR(cell)) {
  		afs_put_cell(net, cell);
  		return 0;
  	}
  
  	ret = dns_query(net->net, "afsdb", name, len, "srv=1",
  			NULL, NULL, false);
  	if (ret == -ENODATA)
  		ret = -EDESTADDRREQ;
  	return ret;
  }
  
  /*
   * Try to auto mount the mountpoint with pseudo directory, if the autocell
   * operation is setted.
   */
  struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
  {
  	struct afs_vnode *vnode = AFS_FS_I(dir);
  	struct inode *inode;
  	int ret = -ENOENT;
  
  	_enter("%p{%pd}, {%llx:%llu}",
  	       dentry, dentry, vnode->fid.vid, vnode->fid.vnode);
  
  	if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
  		goto out;
  
  	ret = afs_probe_cell_name(dentry);
  	if (ret < 0)
  		goto out;
  
  	inode = afs_iget_pseudo_dir(dir->i_sb, false);
  	if (IS_ERR(inode)) {
  		ret = PTR_ERR(inode);
  		goto out;
  	}
  
  	_leave("= %p", inode);
  	return inode;
  
  out:
  	_leave("= %d", ret);
  	return ret == -ENOENT ? NULL : ERR_PTR(ret);
  }
  
  /*
   * Look up @cell in a dynroot directory.  This is a substitution for the
   * local cell name for the net namespace.
   */
  static struct dentry *afs_lookup_atcell(struct dentry *dentry)
  {
  	struct afs_cell *cell;
  	struct afs_net *net = afs_d2net(dentry);
  	struct dentry *ret;
  	unsigned int seq = 0;
  	char *name;
  	int len;
  
  	if (!net->ws_cell)
  		return ERR_PTR(-ENOENT);
  
  	ret = ERR_PTR(-ENOMEM);
  	name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
  	if (!name)
  		goto out_p;
  
  	rcu_read_lock();
  	do {
  		read_seqbegin_or_lock(&net->cells_lock, &seq);
  		cell = rcu_dereference_raw(net->ws_cell);
  		if (cell) {
  			len = cell->name_len;
  			memcpy(name, cell->name, len + 1);
  		}
  	} while (need_seqretry(&net->cells_lock, seq));
  	done_seqretry(&net->cells_lock, seq);
  	rcu_read_unlock();
  
  	ret = ERR_PTR(-ENOENT);
  	if (!cell)
  		goto out_n;
  
  	ret = lookup_one_len(name, dentry->d_parent, len);
  
  	/* We don't want to d_add() the @cell dentry here as we don't want to
  	 * the cached dentry to hide changes to the local cell name.
  	 */
  
  out_n:
  	kfree(name);
  out_p:
  	return ret;
  }
  
  /*
   * Look up an entry in a dynroot directory.
   */
  static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
  					 unsigned int flags)
  {
  	_enter("%pd", dentry);
  
  	ASSERTCMP(d_inode(dentry), ==, NULL);
  
  	if (flags & LOOKUP_CREATE)
  		return ERR_PTR(-EOPNOTSUPP);
  
  	if (dentry->d_name.len >= AFSNAMEMAX) {
  		_leave(" = -ENAMETOOLONG");
  		return ERR_PTR(-ENAMETOOLONG);
  	}
  
  	if (dentry->d_name.len == 5 &&
  	    memcmp(dentry->d_name.name, "@cell", 5) == 0)
  		return afs_lookup_atcell(dentry);
  
  	return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
  }
  
  const struct inode_operations afs_dynroot_inode_operations = {
  	.lookup		= afs_dynroot_lookup,
  };
  
  /*
   * Dirs in the dynamic root don't need revalidation.
   */
  static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
  {
  	return 1;
  }
  
  /*
   * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
   * sleep)
   * - called from dput() when d_count is going to 0.
   * - return 1 to request dentry be unhashed, 0 otherwise
   */
  static int afs_dynroot_d_delete(const struct dentry *dentry)
  {
  	return d_really_is_positive(dentry);
  }
  
  const struct dentry_operations afs_dynroot_dentry_operations = {
  	.d_revalidate	= afs_dynroot_d_revalidate,
  	.d_delete	= afs_dynroot_d_delete,
  	.d_release	= afs_d_release,
  	.d_automount	= afs_d_automount,
  };
  
  /*
   * Create a manually added cell mount directory.
   * - The caller must hold net->proc_cells_lock
   */
  int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
  {
  	struct super_block *sb = net->dynroot_sb;
  	struct dentry *root, *subdir;
  	int ret;
  
  	if (!sb || atomic_read(&sb->s_active) == 0)
  		return 0;
  
  	/* Let the ->lookup op do the creation */
  	root = sb->s_root;
  	inode_lock(root->d_inode);
  	subdir = lookup_one_len(cell->name, root, cell->name_len);
  	if (IS_ERR(subdir)) {
  		ret = PTR_ERR(subdir);
  		goto unlock;
  	}
  
  	/* Note that we're retaining an extra ref on the dentry */
  	subdir->d_fsdata = (void *)1UL;
  	ret = 0;
  unlock:
  	inode_unlock(root->d_inode);
  	return ret;
  }
  
  /*
   * Remove a manually added cell mount directory.
   * - The caller must hold net->proc_cells_lock
   */
  void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
  {
  	struct super_block *sb = net->dynroot_sb;
  	struct dentry *root, *subdir;
  
  	if (!sb || atomic_read(&sb->s_active) == 0)
  		return;
  
  	root = sb->s_root;
  	inode_lock(root->d_inode);
  
  	/* Don't want to trigger a lookup call, which will re-add the cell */
  	subdir = try_lookup_one_len(cell->name, root, cell->name_len);
  	if (IS_ERR_OR_NULL(subdir)) {
  		_debug("lookup %ld", PTR_ERR(subdir));
  		goto no_dentry;
  	}
  
  	_debug("rmdir %pd %u", subdir, d_count(subdir));
  
  	if (subdir->d_fsdata) {
  		_debug("unpin %u", d_count(subdir));
  		subdir->d_fsdata = NULL;
  		dput(subdir);
  	}
  	dput(subdir);
  no_dentry:
  	inode_unlock(root->d_inode);
  	_leave("");
  }
  
  /*
   * Populate a newly created dynamic root with cell names.
   */
  int afs_dynroot_populate(struct super_block *sb)
  {
  	struct afs_cell *cell;
  	struct afs_net *net = afs_sb2net(sb);
  	int ret;
  
  	mutex_lock(&net->proc_cells_lock);
  
  	net->dynroot_sb = sb;
  	hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
  		ret = afs_dynroot_mkdir(net, cell);
  		if (ret < 0)
  			goto error;
  	}
  
  	ret = 0;
  out:
  	mutex_unlock(&net->proc_cells_lock);
  	return ret;
  
  error:
  	net->dynroot_sb = NULL;
  	goto out;
  }
  
  /*
   * When a dynamic root that's in the process of being destroyed, depopulate it
   * of pinned directories.
   */
  void afs_dynroot_depopulate(struct super_block *sb)
  {
  	struct afs_net *net = afs_sb2net(sb);
  	struct dentry *root = sb->s_root, *subdir, *tmp;
  
  	/* Prevent more subdirs from being created */
  	mutex_lock(&net->proc_cells_lock);
  	if (net->dynroot_sb == sb)
  		net->dynroot_sb = NULL;
  	mutex_unlock(&net->proc_cells_lock);
  
  	inode_lock(root->d_inode);
  
  	/* Remove all the pins for dirs created for manually added cells */
  	list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
  		if (subdir->d_fsdata) {
  			subdir->d_fsdata = NULL;
  			dput(subdir);
  		}
  	}
  
  	inode_unlock(root->d_inode);
  }
  