1// SPDX-License-Identifier: GPL-2.0-or-later
  2/* AFS dynamic root handling
  3 *
  4 * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
  5 * Written by David Howells (dhowells@redhat.com)
  6 */
  7
  8#include <linux/fs.h>
  9#include <linux/namei.h>
 10#include <linux/dns_resolver.h>
 11#include "internal.h"
 12
 13static atomic_t afs_autocell_ino;
 14
 15/*
 16 * iget5() comparator for inode created by autocell operations
 17 *
 18 * These pseudo inodes don't match anything.
 19 */
 20static int afs_iget5_pseudo_test(struct inode *inode, void *opaque)
 21{
 22	return 0;
 23}
 24
 25/*
 26 * iget5() inode initialiser
 27 */
 28static int afs_iget5_pseudo_set(struct inode *inode, void *opaque)
 29{
 30	struct afs_super_info *as = AFS_FS_S(inode->i_sb);
 31	struct afs_vnode *vnode = AFS_FS_I(inode);
 32	struct afs_fid *fid = opaque;
 33
 34	vnode->volume		= as->volume;
 35	vnode->fid		= *fid;
 36	inode->i_ino		= fid->vnode;
 37	inode->i_generation	= fid->unique;
 38	return 0;
 39}
 40
 41/*
 42 * Create an inode for a dynamic root directory or an autocell dynamic
 43 * automount dir.
 44 */
 45struct inode *afs_iget_pseudo_dir(struct super_block *sb, bool root)
 46{
 47	struct afs_super_info *as = AFS_FS_S(sb);
 48	struct afs_vnode *vnode;
 49	struct inode *inode;
 50	struct afs_fid fid = {};
 51
 52	_enter("");
 53
 54	if (as->volume)
 55		fid.vid = as->volume->vid;
 56	if (root) {
 57		fid.vnode = 1;
 58		fid.unique = 1;
 59	} else {
 60		fid.vnode = atomic_inc_return(&afs_autocell_ino);
 61		fid.unique = 0;
 62	}
 63
 64	inode = iget5_locked(sb, fid.vnode,
 65			     afs_iget5_pseudo_test, afs_iget5_pseudo_set, &fid);
 66	if (!inode) {
 67		_leave(" = -ENOMEM");
 68		return ERR_PTR(-ENOMEM);
 69	}
 70
 71	_debug("GOT INODE %p { ino=%lu, vl=%llx, vn=%llx, u=%x }",
 72	       inode, inode->i_ino, fid.vid, fid.vnode, fid.unique);
 73
 74	vnode = AFS_FS_I(inode);
 75
 76	/* there shouldn't be an existing inode */
 77	BUG_ON(!(inode->i_state & I_NEW));
 78
 79	netfs_inode_init(&vnode->netfs, NULL);
 80	inode->i_size		= 0;
 81	inode->i_mode		= S_IFDIR | S_IRUGO | S_IXUGO;
 82	if (root) {
 83		inode->i_op	= &afs_dynroot_inode_operations;
 84		inode->i_fop	= &simple_dir_operations;
 85	} else {
 86		inode->i_op	= &afs_autocell_inode_operations;
 87	}
 88	set_nlink(inode, 2);
 89	inode->i_uid		= GLOBAL_ROOT_UID;
 90	inode->i_gid		= GLOBAL_ROOT_GID;
 91	inode->i_ctime = inode->i_atime = inode->i_mtime = current_time(inode);
 92	inode->i_blocks		= 0;
 93	inode->i_generation	= 0;
 94
 95	set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
 96	if (!root) {
 97		set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);
 98		inode->i_flags |= S_AUTOMOUNT;
 99	}
100
101	inode->i_flags |= S_NOATIME;
102	unlock_new_inode(inode);
103	_leave(" = %p", inode);
104	return inode;
105}
106
107/*
108 * Probe to see if a cell may exist.  This prevents positive dentries from
109 * being created unnecessarily.
110 */
111static int afs_probe_cell_name(struct dentry *dentry)
112{
113	struct afs_cell *cell;
114	struct afs_net *net = afs_d2net(dentry);
115	const char *name = dentry->d_name.name;
116	size_t len = dentry->d_name.len;
117	int ret;
118
119	/* Names prefixed with a dot are R/W mounts. */
120	if (name[0] == '.') {
121		if (len == 1)
122			return -EINVAL;
123		name++;
124		len--;
125	}
126
127	cell = afs_find_cell(net, name, len, afs_cell_trace_use_probe);
128	if (!IS_ERR(cell)) {
129		afs_unuse_cell(net, cell, afs_cell_trace_unuse_probe);
130		return 0;
131	}
132
133	ret = dns_query(net->net, "afsdb", name, len, "srv=1",
134			NULL, NULL, false);
135	if (ret == -ENODATA)
136		ret = -EDESTADDRREQ;
137	return ret;
138}
139
140/*
141 * Try to auto mount the mountpoint with pseudo directory, if the autocell
142 * operation is setted.
143 */
144struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
145{
146	struct afs_vnode *vnode = AFS_FS_I(dir);
147	struct inode *inode;
148	int ret = -ENOENT;
149
150	_enter("%p{%pd}, {%llx:%llu}",
151	       dentry, dentry, vnode->fid.vid, vnode->fid.vnode);
152
153	if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
154		goto out;
155
156	ret = afs_probe_cell_name(dentry);
157	if (ret < 0)
158		goto out;
159
160	inode = afs_iget_pseudo_dir(dir->i_sb, false);
161	if (IS_ERR(inode)) {
162		ret = PTR_ERR(inode);
163		goto out;
164	}
165
166	_leave("= %p", inode);
167	return inode;
168
169out:
170	_leave("= %d", ret);
171	return ret == -ENOENT ? NULL : ERR_PTR(ret);
172}
173
174/*
175 * Look up @cell in a dynroot directory.  This is a substitution for the
176 * local cell name for the net namespace.
177 */
178static struct dentry *afs_lookup_atcell(struct dentry *dentry)
179{
180	struct afs_cell *cell;
181	struct afs_net *net = afs_d2net(dentry);
182	struct dentry *ret;
183	char *name;
184	int len;
185
186	if (!net->ws_cell)
187		return ERR_PTR(-ENOENT);
188
189	ret = ERR_PTR(-ENOMEM);
190	name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
191	if (!name)
192		goto out_p;
193
194	down_read(&net->cells_lock);
195	cell = net->ws_cell;
196	if (cell) {
197		len = cell->name_len;
198		memcpy(name, cell->name, len + 1);
199	}
200	up_read(&net->cells_lock);
201
202	ret = ERR_PTR(-ENOENT);
203	if (!cell)
204		goto out_n;
205
206	ret = lookup_one_len(name, dentry->d_parent, len);
207
208	/* We don't want to d_add() the @cell dentry here as we don't want to
209	 * the cached dentry to hide changes to the local cell name.
210	 */
211
212out_n:
213	kfree(name);
214out_p:
215	return ret;
216}
217
218/*
219 * Look up an entry in a dynroot directory.
220 */
221static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
222					 unsigned int flags)
223{
224	_enter("%pd", dentry);
225
226	ASSERTCMP(d_inode(dentry), ==, NULL);
227
228	if (flags & LOOKUP_CREATE)
229		return ERR_PTR(-EOPNOTSUPP);
230
231	if (dentry->d_name.len >= AFSNAMEMAX) {
232		_leave(" = -ENAMETOOLONG");
233		return ERR_PTR(-ENAMETOOLONG);
234	}
235
236	if (dentry->d_name.len == 5 &&
237	    memcmp(dentry->d_name.name, "@cell", 5) == 0)
238		return afs_lookup_atcell(dentry);
239
240	return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
241}
242
243const struct inode_operations afs_dynroot_inode_operations = {
244	.lookup		= afs_dynroot_lookup,
245};
246
247/*
248 * Dirs in the dynamic root don't need revalidation.
249 */
250static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
251{
252	return 1;
253}
254
255/*
256 * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
257 * sleep)
258 * - called from dput() when d_count is going to 0.
259 * - return 1 to request dentry be unhashed, 0 otherwise
260 */
261static int afs_dynroot_d_delete(const struct dentry *dentry)
262{
263	return d_really_is_positive(dentry);
264}
265
266const struct dentry_operations afs_dynroot_dentry_operations = {
267	.d_revalidate	= afs_dynroot_d_revalidate,
268	.d_delete	= afs_dynroot_d_delete,
269	.d_release	= afs_d_release,
270	.d_automount	= afs_d_automount,
271};
272
273/*
274 * Create a manually added cell mount directory.
275 * - The caller must hold net->proc_cells_lock
276 */
277int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
278{
279	struct super_block *sb = net->dynroot_sb;
280	struct dentry *root, *subdir;
281	int ret;
282
283	if (!sb || atomic_read(&sb->s_active) == 0)
284		return 0;
285
286	/* Let the ->lookup op do the creation */
287	root = sb->s_root;
288	inode_lock(root->d_inode);
289	subdir = lookup_one_len(cell->name, root, cell->name_len);
290	if (IS_ERR(subdir)) {
291		ret = PTR_ERR(subdir);
292		goto unlock;
293	}
294
295	/* Note that we're retaining an extra ref on the dentry */
296	subdir->d_fsdata = (void *)1UL;
297	ret = 0;
298unlock:
299	inode_unlock(root->d_inode);
300	return ret;
301}
302
303/*
304 * Remove a manually added cell mount directory.
305 * - The caller must hold net->proc_cells_lock
306 */
307void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
308{
309	struct super_block *sb = net->dynroot_sb;
310	struct dentry *root, *subdir;
311
312	if (!sb || atomic_read(&sb->s_active) == 0)
313		return;
314
315	root = sb->s_root;
316	inode_lock(root->d_inode);
317
318	/* Don't want to trigger a lookup call, which will re-add the cell */
319	subdir = try_lookup_one_len(cell->name, root, cell->name_len);
320	if (IS_ERR_OR_NULL(subdir)) {
321		_debug("lookup %ld", PTR_ERR(subdir));
322		goto no_dentry;
323	}
324
325	_debug("rmdir %pd %u", subdir, d_count(subdir));
326
327	if (subdir->d_fsdata) {
328		_debug("unpin %u", d_count(subdir));
329		subdir->d_fsdata = NULL;
330		dput(subdir);
331	}
332	dput(subdir);
333no_dentry:
334	inode_unlock(root->d_inode);
335	_leave("");
336}
337
338/*
339 * Populate a newly created dynamic root with cell names.
340 */
341int afs_dynroot_populate(struct super_block *sb)
342{
343	struct afs_cell *cell;
344	struct afs_net *net = afs_sb2net(sb);
345	int ret;
346
347	mutex_lock(&net->proc_cells_lock);
348
349	net->dynroot_sb = sb;
350	hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
351		ret = afs_dynroot_mkdir(net, cell);
352		if (ret < 0)
353			goto error;
354	}
355
356	ret = 0;
357out:
358	mutex_unlock(&net->proc_cells_lock);
359	return ret;
360
361error:
362	net->dynroot_sb = NULL;
363	goto out;
364}
365
366/*
367 * When a dynamic root that's in the process of being destroyed, depopulate it
368 * of pinned directories.
369 */
370void afs_dynroot_depopulate(struct super_block *sb)
371{
372	struct afs_net *net = afs_sb2net(sb);
373	struct dentry *root = sb->s_root, *subdir, *tmp;
374
375	/* Prevent more subdirs from being created */
376	mutex_lock(&net->proc_cells_lock);
377	if (net->dynroot_sb == sb)
378		net->dynroot_sb = NULL;
379	mutex_unlock(&net->proc_cells_lock);
380
381	if (root) {
382		inode_lock(root->d_inode);
383
384		/* Remove all the pins for dirs created for manually added cells */
385		list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
386			if (subdir->d_fsdata) {
387				subdir->d_fsdata = NULL;
388				dput(subdir);
389			}
390		}
391
392		inode_unlock(root->d_inode);
393	}
394}