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	= generic_delete_inode,
61	.evict_inode	= kernfs_evict_inode,
62
63	.show_options	= kernfs_sop_show_options,
64	.show_path	= kernfs_sop_show_path,
65};
66
67static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
68			    struct inode *parent)
69{
70	struct kernfs_node *kn = inode->i_private;
71
72	if (*max_len < 2) {
73		*max_len = 2;
74		return FILEID_INVALID;
75	}
76
77	*max_len = 2;
78	*(u64 *)fh = kn->id;
79	return FILEID_KERNFS;
80}
81
82static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
83					    struct fid *fid, int fh_len,
84					    int fh_type, bool get_parent)
85{
86	struct kernfs_super_info *info = kernfs_info(sb);
87	struct kernfs_node *kn;
88	struct inode *inode;
89	u64 id;
90
91	if (fh_len < 2)
92		return NULL;
93
94	switch (fh_type) {
95	case FILEID_KERNFS:
96		id = *(u64 *)fid;
97		break;
98	case FILEID_INO32_GEN:
99	case FILEID_INO32_GEN_PARENT:
100		/*
101		 * blk_log_action() exposes "LOW32,HIGH32" pair without
102		 * type and userland can call us with generic fid
103		 * constructed from them.  Combine it back to ID.  See
104		 * blk_log_action().
105		 */
106		id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
107		break;
108	default:
109		return NULL;
110	}
111
112	kn = kernfs_find_and_get_node_by_id(info->root, id);
113	if (!kn)
114		return ERR_PTR(-ESTALE);
115
116	if (get_parent) {
117		struct kernfs_node *parent;
118
119		parent = kernfs_get_parent(kn);
120		kernfs_put(kn);
121		kn = parent;
122		if (!kn)
123			return ERR_PTR(-ESTALE);
124	}
125
126	inode = kernfs_get_inode(sb, kn);
127	kernfs_put(kn);
128	return d_obtain_alias(inode);
129}
130
131static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
132					  struct fid *fid, int fh_len,
133					  int fh_type)
134{
135	return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
136}
137
138static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
139					  struct fid *fid, int fh_len,
140					  int fh_type)
141{
142	return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
143}
144
145static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
146{
147	struct kernfs_node *kn = kernfs_dentry_node(child);
148
149	return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
150}
151
152static const struct export_operations kernfs_export_ops = {
153	.encode_fh	= kernfs_encode_fh,
154	.fh_to_dentry	= kernfs_fh_to_dentry,
155	.fh_to_parent	= kernfs_fh_to_parent,
156	.get_parent	= kernfs_get_parent_dentry,
157};
158
159/**
160 * kernfs_root_from_sb - determine kernfs_root associated with a super_block
161 * @sb: the super_block in question
162 *
163 * Return: the kernfs_root associated with @sb.  If @sb is not a kernfs one,
164 * %NULL is returned.
165 */
166struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
167{
168	if (sb->s_op == &kernfs_sops)
169		return kernfs_info(sb)->root;
170	return NULL;
171}
172
173/*
174 * find the next ancestor in the path down to @child, where @parent was the
175 * ancestor whose descendant we want to find.
176 *
177 * Say the path is /a/b/c/d.  @child is d, @parent is %NULL.  We return the root
178 * node.  If @parent is b, then we return the node for c.
179 * Passing in d as @parent is not ok.
180 */
181static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
182					      struct kernfs_node *parent)
183{
184	if (child == parent) {
185		pr_crit_once("BUG in find_next_ancestor: called with parent == child");
186		return NULL;
187	}
188
189	while (child->parent != parent) {
190		if (!child->parent)
191			return NULL;
192		child = child->parent;
193	}
194
195	return child;
196}
197
198/**
199 * kernfs_node_dentry - get a dentry for the given kernfs_node
200 * @kn: kernfs_node for which a dentry is needed
201 * @sb: the kernfs super_block
202 *
203 * Return: the dentry pointer
204 */
205struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
206				  struct super_block *sb)
207{
208	struct dentry *dentry;
209	struct kernfs_node *knparent = NULL;
210
211	BUG_ON(sb->s_op != &kernfs_sops);
212
213	dentry = dget(sb->s_root);
214
215	/* Check if this is the root kernfs_node */
216	if (!kn->parent)
217		return dentry;
218
219	knparent = find_next_ancestor(kn, NULL);
220	if (WARN_ON(!knparent)) {
221		dput(dentry);
222		return ERR_PTR(-EINVAL);
223	}
224
225	do {
226		struct dentry *dtmp;
227		struct kernfs_node *kntmp;
228
229		if (kn == knparent)
230			return dentry;
231		kntmp = find_next_ancestor(kn, knparent);
232		if (WARN_ON(!kntmp)) {
233			dput(dentry);
234			return ERR_PTR(-EINVAL);
235		}
236		dtmp = lookup_positive_unlocked(kntmp->name, dentry,
237					       strlen(kntmp->name));
238		dput(dentry);
239		if (IS_ERR(dtmp))
240			return dtmp;
241		knparent = kntmp;
242		dentry = dtmp;
243	} while (true);
244}
245
246static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
247{
248	struct kernfs_super_info *info = kernfs_info(sb);
249	struct kernfs_root *kf_root = kfc->root;
250	struct inode *inode;
251	struct dentry *root;
252
253	info->sb = sb;
254	/* Userspace would break if executables or devices appear on sysfs */
255	sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
256	sb->s_blocksize = PAGE_SIZE;
257	sb->s_blocksize_bits = PAGE_SHIFT;
258	sb->s_magic = kfc->magic;
259	sb->s_op = &kernfs_sops;
260	sb->s_xattr = kernfs_xattr_handlers;
261	if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
262		sb->s_export_op = &kernfs_export_ops;
263	sb->s_time_gran = 1;
264
265	/* sysfs dentries and inodes don't require IO to create */
266	sb->s_shrink->seeks = 0;
267
268	/* get root inode, initialize and unlock it */
269	down_read(&kf_root->kernfs_rwsem);
270	inode = kernfs_get_inode(sb, info->root->kn);
271	up_read(&kf_root->kernfs_rwsem);
272	if (!inode) {
273		pr_debug("kernfs: could not get root inode\n");
274		return -ENOMEM;
275	}
276
277	/* instantiate and link root dentry */
278	root = d_make_root(inode);
279	if (!root) {
280		pr_debug("%s: could not get root dentry!\n", __func__);
281		return -ENOMEM;
282	}
283	sb->s_root = root;
284	sb->s_d_op = &kernfs_dops;
285	return 0;
286}
287
288static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
289{
290	struct kernfs_super_info *sb_info = kernfs_info(sb);
291	struct kernfs_super_info *info = fc->s_fs_info;
292
293	return sb_info->root == info->root && sb_info->ns == info->ns;
294}
295
296static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
297{
298	struct kernfs_fs_context *kfc = fc->fs_private;
299
300	kfc->ns_tag = NULL;
301	return set_anon_super_fc(sb, fc);
302}
303
304/**
305 * kernfs_super_ns - determine the namespace tag of a kernfs super_block
306 * @sb: super_block of interest
307 *
308 * Return: the namespace tag associated with kernfs super_block @sb.
309 */
310const void *kernfs_super_ns(struct super_block *sb)
311{
312	struct kernfs_super_info *info = kernfs_info(sb);
313
314	return info->ns;
315}
316
317/**
318 * kernfs_get_tree - kernfs filesystem access/retrieval helper
319 * @fc: The filesystem context.
320 *
321 * This is to be called from each kernfs user's fs_context->ops->get_tree()
322 * implementation, which should set the specified ->@fs_type and ->@flags, and
323 * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
324 * respectively.
325 *
326 * Return: %0 on success, -errno on failure.
327 */
328int kernfs_get_tree(struct fs_context *fc)
329{
330	struct kernfs_fs_context *kfc = fc->fs_private;
331	struct super_block *sb;
332	struct kernfs_super_info *info;
333	int error;
334
335	info = kzalloc(sizeof(*info), GFP_KERNEL);
336	if (!info)
337		return -ENOMEM;
338
339	info->root = kfc->root;
340	info->ns = kfc->ns_tag;
341	INIT_LIST_HEAD(&info->node);
342
343	fc->s_fs_info = info;
344	sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
345	if (IS_ERR(sb))
346		return PTR_ERR(sb);
347
348	if (!sb->s_root) {
349		struct kernfs_super_info *info = kernfs_info(sb);
350		struct kernfs_root *root = kfc->root;
351
352		kfc->new_sb_created = true;
353
354		error = kernfs_fill_super(sb, kfc);
355		if (error) {
356			deactivate_locked_super(sb);
357			return error;
358		}
359		sb->s_flags |= SB_ACTIVE;
360
361		uuid_t uuid;
362		uuid_gen(&uuid);
363		super_set_uuid(sb, uuid.b, sizeof(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