mount.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * fs/kernfs/mount.c - kernfs mount implementation
  4 *
  5 * Copyright (c) 2001-3 Patrick Mochel
  6 * Copyright (c) 2007 SUSE Linux Products GmbH
  7 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
  8 */
  9
 10#include <linux/fs.h>
 11#include <linux/mount.h>
 12#include <linux/init.h>
 13#include <linux/magic.h>
 14#include <linux/slab.h>
 15#include <linux/pagemap.h>
 16#include <linux/namei.h>
 17#include <linux/seq_file.h>
 18#include <linux/exportfs.h>
 19#include <linux/uuid.h>
 20#include <linux/statfs.h>
 21
 22#include "kernfs-internal.h"
 23
 24struct kmem_cache *kernfs_node_cache __ro_after_init;
 25struct kmem_cache *kernfs_iattrs_cache __ro_after_init;
 26struct kernfs_global_locks *kernfs_locks __ro_after_init;
 27
 28static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
 29{
 30	struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
 31	struct kernfs_syscall_ops *scops = root->syscall_ops;
 32
 33	if (scops && scops->show_options)
 34		return scops->show_options(sf, root);
 35	return 0;
 36}
 37
 38static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
 39{
 40	struct kernfs_node *node = kernfs_dentry_node(dentry);
 41	struct kernfs_root *root = kernfs_root(node);
 42	struct kernfs_syscall_ops *scops = root->syscall_ops;
 43
 44	if (scops && scops->show_path)
 45		return scops->show_path(sf, node, root);
 46
 47	seq_dentry(sf, dentry, " \t\n\\");
 48	return 0;
 49}
 50
 51static int kernfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 52{
 53	simple_statfs(dentry, buf);
 54	buf->f_fsid = uuid_to_fsid(dentry->d_sb->s_uuid.b);
 55	return 0;
 56}
 57
 58const struct super_operations kernfs_sops = {
 59	.statfs		= kernfs_statfs,
 60	.drop_inode	= inode_just_drop,
 61	.evict_inode	= kernfs_evict_inode,
 62
 63	.show_options	= kernfs_sop_show_options,
 64	.show_path	= kernfs_sop_show_path,
 65
 66	/*
 67	 * sysfs is built on top of kernfs and sysfs provides the power
 68	 * management infrastructure to support suspend/hibernate by
 69	 * writing to various files in /sys/power/. As filesystems may
 70	 * be automatically frozen during suspend/hibernate implementing
 71	 * freeze/thaw support for kernfs generically will cause
 72	 * deadlocks as the suspending/hibernation initiating task will
 73	 * hold a VFS lock that it will then wait upon to be released.
 74	 * If freeze/thaw for kernfs is needed talk to the VFS.
 75	 */
 76	.freeze_fs	= NULL,
 77	.unfreeze_fs	= NULL,
 78	.freeze_super	= NULL,
 79	.thaw_super	= NULL,
 80};
 81
 82static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
 83			    struct inode *parent)
 84{
 85	struct kernfs_node *kn = inode->i_private;
 86
 87	if (*max_len < 2) {
 88		*max_len = 2;
 89		return FILEID_INVALID;
 90	}
 91
 92	*max_len = 2;
 93	*(u64 *)fh = kn->id;
 94	return FILEID_KERNFS;
 95}
 96
 97static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
 98					    struct fid *fid, int fh_len,
 99					    int fh_type, bool get_parent)
100{
101	struct kernfs_super_info *info = kernfs_info(sb);
102	struct kernfs_node *kn;
103	struct inode *inode;
104	u64 id;
105
106	if (fh_len < 2)
107		return NULL;
108
109	switch (fh_type) {
110	case FILEID_KERNFS:
111		id = *(u64 *)fid;
112		break;
113	case FILEID_INO32_GEN:
114	case FILEID_INO32_GEN_PARENT:
115		/*
116		 * blk_log_action() exposes "LOW32,HIGH32" pair without
117		 * type and userland can call us with generic fid
118		 * constructed from them.  Combine it back to ID.  See
119		 * blk_log_action().
120		 */
121		id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
122		break;
123	default:
124		return NULL;
125	}
126
127	kn = kernfs_find_and_get_node_by_id(info->root, id);
128	if (!kn)
129		return ERR_PTR(-ESTALE);
130
131	if (get_parent) {
132		struct kernfs_node *parent;
133
134		parent = kernfs_get_parent(kn);
135		kernfs_put(kn);
136		kn = parent;
137		if (!kn)
138			return ERR_PTR(-ESTALE);
139	}
140
141	inode = kernfs_get_inode(sb, kn);
142	kernfs_put(kn);
143	return d_obtain_alias(inode);
144}
145
146static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
147					  struct fid *fid, int fh_len,
148					  int fh_type)
149{
150	return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
151}
152
153static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
154					  struct fid *fid, int fh_len,
155					  int fh_type)
156{
157	return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
158}
159
160static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
161{
162	struct kernfs_node *kn = kernfs_dentry_node(child);
163	struct kernfs_root *root = kernfs_root(kn);
164
165	guard(rwsem_read)(&root->kernfs_rwsem);
166	return d_obtain_alias(kernfs_get_inode(child->d_sb, kernfs_parent(kn)));
167}
168
169static const struct export_operations kernfs_export_ops = {
170	.encode_fh	= kernfs_encode_fh,
171	.fh_to_dentry	= kernfs_fh_to_dentry,
172	.fh_to_parent	= kernfs_fh_to_parent,
173	.get_parent	= kernfs_get_parent_dentry,
174};
175
176/**
177 * kernfs_root_from_sb - determine kernfs_root associated with a super_block
178 * @sb: the super_block in question
179 *
180 * Return: the kernfs_root associated with @sb.  If @sb is not a kernfs one,
181 * %NULL is returned.
182 */
183struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
184{
185	if (sb->s_op == &kernfs_sops)
186		return kernfs_info(sb)->root;
187	return NULL;
188}
189
190/*
191 * find the next ancestor in the path down to @child, where @parent was the
192 * ancestor whose descendant we want to find.
193 *
194 * Say the path is /a/b/c/d.  @child is d, @parent is %NULL.  We return the root
195 * node.  If @parent is b, then we return the node for c.
196 * Passing in d as @parent is not ok.
197 */
198static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
199					      struct kernfs_node *parent)
200{
201	if (child == parent) {
202		pr_crit_once("BUG in find_next_ancestor: called with parent == child");
203		return NULL;
204	}
205
206	while (kernfs_parent(child) != parent) {
207		child = kernfs_parent(child);
208		if (!child)
209			return NULL;
210	}
211
212	return child;
213}
214
215/**
216 * kernfs_node_dentry - get a dentry for the given kernfs_node
217 * @kn: kernfs_node for which a dentry is needed
218 * @sb: the kernfs super_block
219 *
220 * Return: the dentry pointer
221 */
222struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
223				  struct super_block *sb)
224{
225	struct dentry *dentry;
226	struct kernfs_node *knparent;
227	struct kernfs_root *root;
228
229	BUG_ON(sb->s_op != &kernfs_sops);
230
231	dentry = dget(sb->s_root);
232
233	/* Check if this is the root kernfs_node */
234	if (!rcu_access_pointer(kn->__parent))
235		return dentry;
236
237	root = kernfs_root(kn);
238	/*
239	 * As long as kn is valid, its parent can not vanish. This is cgroup's
240	 * kn so it can't have its parent replaced. Therefore it is safe to use
241	 * the ancestor node outside of the RCU or locked section.
242	 */
243	if (WARN_ON_ONCE(!(root->flags & KERNFS_ROOT_INVARIANT_PARENT)))
244		return ERR_PTR(-EINVAL);
245	scoped_guard(rcu) {
246		knparent = find_next_ancestor(kn, NULL);
247	}
248	if (WARN_ON(!knparent)) {
249		dput(dentry);
250		return ERR_PTR(-EINVAL);
251	}
252
253	do {
254		struct dentry *dtmp;
255		struct kernfs_node *kntmp;
256		const char *name;
257
258		if (kn == knparent)
259			return dentry;
260
261		scoped_guard(rwsem_read, &root->kernfs_rwsem) {
262			kntmp = find_next_ancestor(kn, knparent);
263			if (WARN_ON(!kntmp)) {
264				dput(dentry);
265				return ERR_PTR(-EINVAL);
266			}
267			name = kstrdup(kernfs_rcu_name(kntmp), GFP_KERNEL);
268		}
269		if (!name) {
270			dput(dentry);
271			return ERR_PTR(-ENOMEM);
272		}
273		dtmp = lookup_noperm_positive_unlocked(&QSTR(name), dentry);
274		dput(dentry);
275		kfree(name);
276		if (IS_ERR(dtmp))
277			return dtmp;
278		knparent = kntmp;
279		dentry = dtmp;
280	} while (true);
281}
282
283static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
284{
285	struct kernfs_super_info *info = kernfs_info(sb);
286	struct kernfs_root *kf_root = kfc->root;
287	struct inode *inode;
288	struct dentry *root;
289
290	info->sb = sb;
291	/* Userspace would break if executables or devices appear on sysfs */
292	sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
293	sb->s_blocksize = PAGE_SIZE;
294	sb->s_blocksize_bits = PAGE_SHIFT;
295	sb->s_magic = kfc->magic;
296	sb->s_op = &kernfs_sops;
297	sb->s_xattr = kernfs_xattr_handlers;
298	if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
299		sb->s_export_op = &kernfs_export_ops;
300	sb->s_time_gran = 1;
301	sb->s_maxbytes  = MAX_LFS_FILESIZE;
302
303	/* sysfs dentries and inodes don't require IO to create */
304	sb->s_shrink->seeks = 0;
305
306	/* get root inode, initialize and unlock it */
307	down_read(&kf_root->kernfs_rwsem);
308	inode = kernfs_get_inode(sb, info->root->kn);
309	up_read(&kf_root->kernfs_rwsem);
310	if (!inode) {
311		pr_debug("kernfs: could not get root inode\n");
312		return -ENOMEM;
313	}
314
315	/* instantiate and link root dentry */
316	root = d_make_root(inode);
317	if (!root) {
318		pr_debug("%s: could not get root dentry!\n", __func__);
319		return -ENOMEM;
320	}
321	sb->s_root = root;
322	set_default_d_op(sb, &kernfs_dops);
323	return 0;
324}
325
326static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
327{
328	struct kernfs_super_info *sb_info = kernfs_info(sb);
329	struct kernfs_super_info *info = fc->s_fs_info;
330
331	return sb_info->root == info->root && sb_info->ns == info->ns;
332}
333
334static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
335{
336	struct kernfs_fs_context *kfc = fc->fs_private;
337
338	kfc->ns_tag = NULL;
339	return set_anon_super_fc(sb, fc);
340}
341
342/**
343 * kernfs_super_ns - determine the namespace tag of a kernfs super_block
344 * @sb: super_block of interest
345 *
346 * Return: the namespace tag associated with kernfs super_block @sb.
347 */
348const void *kernfs_super_ns(struct super_block *sb)
349{
350	struct kernfs_super_info *info = kernfs_info(sb);
351
352	return info->ns;
353}
354
355/**
356 * kernfs_get_tree - kernfs filesystem access/retrieval helper
357 * @fc: The filesystem context.
358 *
359 * This is to be called from each kernfs user's fs_context->ops->get_tree()
360 * implementation, which should set the specified ->@fs_type and ->@flags, and
361 * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
362 * respectively.
363 *
364 * Return: %0 on success, -errno on failure.
365 */
366int kernfs_get_tree(struct fs_context *fc)
367{
368	struct kernfs_fs_context *kfc = fc->fs_private;
369	struct super_block *sb;
370	struct kernfs_super_info *info;
371	int error;
372
373	info = kzalloc(sizeof(*info), GFP_KERNEL);
374	if (!info)
375		return -ENOMEM;
376
377	info->root = kfc->root;
378	info->ns = kfc->ns_tag;
379	INIT_LIST_HEAD(&info->node);
380
381	fc->s_fs_info = info;
382	sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
383	if (IS_ERR(sb))
384		return PTR_ERR(sb);
385
386	if (!sb->s_root) {
387		struct kernfs_super_info *info = kernfs_info(sb);
388		struct kernfs_root *root = kfc->root;
389
390		kfc->new_sb_created = true;
391
392		error = kernfs_fill_super(sb, kfc);
393		if (error) {
394			deactivate_locked_super(sb);
395			return error;
396		}
397		sb->s_flags |= SB_ACTIVE;
398
399		uuid_t uuid;
400		uuid_gen(&uuid);
401		super_set_uuid(sb, uuid.b, sizeof(uuid));
402
403		down_write(&root->kernfs_supers_rwsem);
404		list_add(&info->node, &info->root->supers);
405		up_write(&root->kernfs_supers_rwsem);
406	}
407
408	fc->root = dget(sb->s_root);
409	return 0;
410}
411
412void kernfs_free_fs_context(struct fs_context *fc)
413{
414	/* Note that we don't deal with kfc->ns_tag here. */
415	kfree(fc->s_fs_info);
416	fc->s_fs_info = NULL;
417}
418
419/**
420 * kernfs_kill_sb - kill_sb for kernfs
421 * @sb: super_block being killed
422 *
423 * This can be used directly for file_system_type->kill_sb().  If a kernfs
424 * user needs extra cleanup, it can implement its own kill_sb() and call
425 * this function at the end.
426 */
427void kernfs_kill_sb(struct super_block *sb)
428{
429	struct kernfs_super_info *info = kernfs_info(sb);
430	struct kernfs_root *root = info->root;
431
432	down_write(&root->kernfs_supers_rwsem);
433	list_del(&info->node);
434	up_write(&root->kernfs_supers_rwsem);
435
436	/*
437	 * Remove the superblock from fs_supers/s_instances
438	 * so we can't find it, before freeing kernfs_super_info.
439	 */
440	kill_anon_super(sb);
441	kfree(info);
442}
443
444static void __init kernfs_mutex_init(void)
445{
446	int count;
447
448	for (count = 0; count < NR_KERNFS_LOCKS; count++)
449		mutex_init(&kernfs_locks->open_file_mutex[count]);
450}
451
452static void __init kernfs_lock_init(void)
453{
454	kernfs_locks = kmalloc(sizeof(struct kernfs_global_locks), GFP_KERNEL);
455	WARN_ON(!kernfs_locks);
456
457	kernfs_mutex_init();
458}
459
460void __init kernfs_init(void)
461{
462	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
463					      sizeof(struct kernfs_node),
464					      0, SLAB_PANIC, NULL);
465
466	/* Creates slab cache for kernfs inode attributes */
467	kernfs_iattrs_cache  = kmem_cache_create("kernfs_iattrs_cache",
468					      sizeof(struct kernfs_iattrs),
469					      0, SLAB_PANIC, NULL);
470
471	kernfs_lock_init();
472}