xref: /kernel/linux/linux-6.6/fs/kernfs/mount.c (revision 62306a36) 
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, *kernfs_iattrs_cache;
25struct kernfs_global_locks *kernfs_locks;
26
27static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
28{
29	struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
30	struct kernfs_syscall_ops *scops = root->syscall_ops;
31
32	if (scops && scops->show_options)
33		return scops->show_options(sf, root);
34	return 0;
35}
36
37static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
38{
39	struct kernfs_node *node = kernfs_dentry_node(dentry);
40	struct kernfs_root *root = kernfs_root(node);
41	struct kernfs_syscall_ops *scops = root->syscall_ops;
42
43	if (scops && scops->show_path)
44		return scops->show_path(sf, node, root);
45
46	seq_dentry(sf, dentry, " \t\n\\");
47	return 0;
48}
49
50static int kernfs_statfs(struct dentry *dentry, struct kstatfs *buf)
51{
52	simple_statfs(dentry, buf);
53	buf->f_fsid = uuid_to_fsid(dentry->d_sb->s_uuid.b);
54	return 0;
55}
56
57const struct super_operations kernfs_sops = {
58	.statfs		= kernfs_statfs,
59	.drop_inode	= generic_delete_inode,
60	.evict_inode	= kernfs_evict_inode,
61
62	.show_options	= kernfs_sop_show_options,
63	.show_path	= kernfs_sop_show_path,
64};
65
66static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
67			    struct inode *parent)
68{
69	struct kernfs_node *kn = inode->i_private;
70
71	if (*max_len < 2) {
72		*max_len = 2;
73		return FILEID_INVALID;
74	}
75
76	*max_len = 2;
77	*(u64 *)fh = kn->id;
78	return FILEID_KERNFS;
79}
80
81static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
82					    struct fid *fid, int fh_len,
83					    int fh_type, bool get_parent)
84{
85	struct kernfs_super_info *info = kernfs_info(sb);
86	struct kernfs_node *kn;
87	struct inode *inode;
88	u64 id;
89
90	if (fh_len < 2)
91		return NULL;
92
93	switch (fh_type) {
94	case FILEID_KERNFS:
95		id = *(u64 *)fid;
96		break;
97	case FILEID_INO32_GEN:
98	case FILEID_INO32_GEN_PARENT:
99		/*
100		 * blk_log_action() exposes "LOW32,HIGH32" pair without
101		 * type and userland can call us with generic fid
102		 * constructed from them.  Combine it back to ID.  See
103		 * blk_log_action().
104		 */
105		id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
106		break;
107	default:
108		return NULL;
109	}
110
111	kn = kernfs_find_and_get_node_by_id(info->root, id);
112	if (!kn)
113		return ERR_PTR(-ESTALE);
114
115	if (get_parent) {
116		struct kernfs_node *parent;
117
118		parent = kernfs_get_parent(kn);
119		kernfs_put(kn);
120		kn = parent;
121		if (!kn)
122			return ERR_PTR(-ESTALE);
123	}
124
125	inode = kernfs_get_inode(sb, kn);
126	kernfs_put(kn);
127	if (!inode)
128		return ERR_PTR(-ESTALE);
129
130	return d_obtain_alias(inode);
131}
132
133static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
134					  struct fid *fid, int fh_len,
135					  int fh_type)
136{
137	return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
138}
139
140static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
141					  struct fid *fid, int fh_len,
142					  int fh_type)
143{
144	return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
145}
146
147static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
148{
149	struct kernfs_node *kn = kernfs_dentry_node(child);
150
151	return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
152}
153
154static const struct export_operations kernfs_export_ops = {
155	.encode_fh	= kernfs_encode_fh,
156	.fh_to_dentry	= kernfs_fh_to_dentry,
157	.fh_to_parent	= kernfs_fh_to_parent,
158	.get_parent	= kernfs_get_parent_dentry,
159};
160
161/**
162 * kernfs_root_from_sb - determine kernfs_root associated with a super_block
163 * @sb: the super_block in question
164 *
165 * Return: the kernfs_root associated with @sb.  If @sb is not a kernfs one,
166 * %NULL is returned.
167 */
168struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
169{
170	if (sb->s_op == &kernfs_sops)
171		return kernfs_info(sb)->root;
172	return NULL;
173}
174
175/*
176 * find the next ancestor in the path down to @child, where @parent was the
177 * ancestor whose descendant we want to find.
178 *
179 * Say the path is /a/b/c/d.  @child is d, @parent is %NULL.  We return the root
180 * node.  If @parent is b, then we return the node for c.
181 * Passing in d as @parent is not ok.
182 */
183static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
184					      struct kernfs_node *parent)
185{
186	if (child == parent) {
187		pr_crit_once("BUG in find_next_ancestor: called with parent == child");
188		return NULL;
189	}
190
191	while (child->parent != parent) {
192		if (!child->parent)
193			return NULL;
194		child = child->parent;
195	}
196
197	return child;
198}
199
200/**
201 * kernfs_node_dentry - get a dentry for the given kernfs_node
202 * @kn: kernfs_node for which a dentry is needed
203 * @sb: the kernfs super_block
204 *
205 * Return: the dentry pointer
206 */
207struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
208				  struct super_block *sb)
209{
210	struct dentry *dentry;
211	struct kernfs_node *knparent = NULL;
212
213	BUG_ON(sb->s_op != &kernfs_sops);
214
215	dentry = dget(sb->s_root);
216
217	/* Check if this is the root kernfs_node */
218	if (!kn->parent)
219		return dentry;
220
221	knparent = find_next_ancestor(kn, NULL);
222	if (WARN_ON(!knparent)) {
223		dput(dentry);
224		return ERR_PTR(-EINVAL);
225	}
226
227	do {
228		struct dentry *dtmp;
229		struct kernfs_node *kntmp;
230
231		if (kn == knparent)
232			return dentry;
233		kntmp = find_next_ancestor(kn, knparent);
234		if (WARN_ON(!kntmp)) {
235			dput(dentry);
236			return ERR_PTR(-EINVAL);
237		}
238		dtmp = lookup_positive_unlocked(kntmp->name, dentry,
239					       strlen(kntmp->name));
240		dput(dentry);
241		if (IS_ERR(dtmp))
242			return dtmp;
243		knparent = kntmp;
244		dentry = dtmp;
245	} while (true);
246}
247
248static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
249{
250	struct kernfs_super_info *info = kernfs_info(sb);
251	struct kernfs_root *kf_root = kfc->root;
252	struct inode *inode;
253	struct dentry *root;
254
255	info->sb = sb;
256	/* Userspace would break if executables or devices appear on sysfs */
257	sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
258	sb->s_blocksize = PAGE_SIZE;
259	sb->s_blocksize_bits = PAGE_SHIFT;
260	sb->s_magic = kfc->magic;
261	sb->s_op = &kernfs_sops;
262	sb->s_xattr = kernfs_xattr_handlers;
263	if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
264		sb->s_export_op = &kernfs_export_ops;
265	sb->s_time_gran = 1;
266
267	/* sysfs dentries and inodes don't require IO to create */
268	sb->s_shrink.seeks = 0;
269
270	/* get root inode, initialize and unlock it */
271	down_read(&kf_root->kernfs_rwsem);
272	inode = kernfs_get_inode(sb, info->root->kn);
273	up_read(&kf_root->kernfs_rwsem);
274	if (!inode) {
275		pr_debug("kernfs: could not get root inode\n");
276		return -ENOMEM;
277	}
278
279	/* instantiate and link root dentry */
280	root = d_make_root(inode);
281	if (!root) {
282		pr_debug("%s: could not get root dentry!\n", __func__);
283		return -ENOMEM;
284	}
285	sb->s_root = root;
286	sb->s_d_op = &kernfs_dops;
287	return 0;
288}
289
290static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
291{
292	struct kernfs_super_info *sb_info = kernfs_info(sb);
293	struct kernfs_super_info *info = fc->s_fs_info;
294
295	return sb_info->root == info->root && sb_info->ns == info->ns;
296}
297
298static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
299{
300	struct kernfs_fs_context *kfc = fc->fs_private;
301
302	kfc->ns_tag = NULL;
303	return set_anon_super_fc(sb, fc);
304}
305
306/**
307 * kernfs_super_ns - determine the namespace tag of a kernfs super_block
308 * @sb: super_block of interest
309 *
310 * Return: the namespace tag associated with kernfs super_block @sb.
311 */
312const void *kernfs_super_ns(struct super_block *sb)
313{
314	struct kernfs_super_info *info = kernfs_info(sb);
315
316	return info->ns;
317}
318
319/**
320 * kernfs_get_tree - kernfs filesystem access/retrieval helper
321 * @fc: The filesystem context.
322 *
323 * This is to be called from each kernfs user's fs_context->ops->get_tree()
324 * implementation, which should set the specified ->@fs_type and ->@flags, and
325 * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
326 * respectively.
327 *
328 * Return: %0 on success, -errno on failure.
329 */
330int kernfs_get_tree(struct fs_context *fc)
331{
332	struct kernfs_fs_context *kfc = fc->fs_private;
333	struct super_block *sb;
334	struct kernfs_super_info *info;
335	int error;
336
337	info = kzalloc(sizeof(*info), GFP_KERNEL);
338	if (!info)
339		return -ENOMEM;
340
341	info->root = kfc->root;
342	info->ns = kfc->ns_tag;
343	INIT_LIST_HEAD(&info->node);
344
345	fc->s_fs_info = info;
346	sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
347	if (IS_ERR(sb))
348		return PTR_ERR(sb);
349
350	if (!sb->s_root) {
351		struct kernfs_super_info *info = kernfs_info(sb);
352		struct kernfs_root *root = kfc->root;
353
354		kfc->new_sb_created = true;
355
356		error = kernfs_fill_super(sb, kfc);
357		if (error) {
358			deactivate_locked_super(sb);
359			return error;
360		}
361		sb->s_flags |= SB_ACTIVE;
362
363		uuid_gen(&sb->s_uuid);
364
365		down_write(&root->kernfs_supers_rwsem);
366		list_add(&info->node, &info->root->supers);
367		up_write(&root->kernfs_supers_rwsem);
368	}
369
370	fc->root = dget(sb->s_root);
371	return 0;
372}
373
374void kernfs_free_fs_context(struct fs_context *fc)
375{
376	/* Note that we don't deal with kfc->ns_tag here. */
377	kfree(fc->s_fs_info);
378	fc->s_fs_info = NULL;
379}
380
381/**
382 * kernfs_kill_sb - kill_sb for kernfs
383 * @sb: super_block being killed
384 *
385 * This can be used directly for file_system_type->kill_sb().  If a kernfs
386 * user needs extra cleanup, it can implement its own kill_sb() and call
387 * this function at the end.
388 */
389void kernfs_kill_sb(struct super_block *sb)
390{
391	struct kernfs_super_info *info = kernfs_info(sb);
392	struct kernfs_root *root = info->root;
393
394	down_write(&root->kernfs_supers_rwsem);
395	list_del(&info->node);
396	up_write(&root->kernfs_supers_rwsem);
397
398	/*
399	 * Remove the superblock from fs_supers/s_instances
400	 * so we can't find it, before freeing kernfs_super_info.
401	 */
402	kill_anon_super(sb);
403	kfree(info);
404}
405
406static void __init kernfs_mutex_init(void)
407{
408	int count;
409
410	for (count = 0; count < NR_KERNFS_LOCKS; count++)
411		mutex_init(&kernfs_locks->open_file_mutex[count]);
412}
413
414static void __init kernfs_lock_init(void)
415{
416	kernfs_locks = kmalloc(sizeof(struct kernfs_global_locks), GFP_KERNEL);
417	WARN_ON(!kernfs_locks);
418
419	kernfs_mutex_init();
420}
421
422void __init kernfs_init(void)
423{
424	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
425					      sizeof(struct kernfs_node),
426					      0, SLAB_PANIC, NULL);
427
428	/* Creates slab cache for kernfs inode attributes */
429	kernfs_iattrs_cache  = kmem_cache_create("kernfs_iattrs_cache",
430					      sizeof(struct kernfs_iattrs),
431					      0, SLAB_PANIC, NULL);
432
433	kernfs_lock_init();
434}
435