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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
20#include "kernfs-internal.h"
21
22struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;
23
24static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
25{
26 struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
27 struct kernfs_syscall_ops *scops = root->syscall_ops;
28
29 if (scops && scops->show_options)
30 return scops->show_options(sf, root);
31 return 0;
32}
33
34static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
35{
36 struct kernfs_node *node = kernfs_dentry_node(dentry);
37 struct kernfs_root *root = kernfs_root(node);
38 struct kernfs_syscall_ops *scops = root->syscall_ops;
39
40 if (scops && scops->show_path)
41 return scops->show_path(sf, node, root);
42
43 seq_dentry(sf, dentry, " \t\n\\");
44 return 0;
45}
46
47const struct super_operations kernfs_sops = {
48 .statfs = simple_statfs,
49 .drop_inode = generic_delete_inode,
50 .evict_inode = kernfs_evict_inode,
51
52 .show_options = kernfs_sop_show_options,
53 .show_path = kernfs_sop_show_path,
54};
55
56/*
57 * Similar to kernfs_fh_get_inode, this one gets kernfs node from inode
58 * number and generation
59 */
60struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root,
61 const union kernfs_node_id *id)
62{
63 struct kernfs_node *kn;
64
65 kn = kernfs_find_and_get_node_by_ino(root, id->ino);
66 if (!kn)
67 return NULL;
68 if (kn->id.generation != id->generation) {
69 kernfs_put(kn);
70 return NULL;
71 }
72 return kn;
73}
74
75static struct inode *kernfs_fh_get_inode(struct super_block *sb,
76 u64 ino, u32 generation)
77{
78 struct kernfs_super_info *info = kernfs_info(sb);
79 struct inode *inode;
80 struct kernfs_node *kn;
81
82 if (ino == 0)
83 return ERR_PTR(-ESTALE);
84
85 kn = kernfs_find_and_get_node_by_ino(info->root, ino);
86 if (!kn)
87 return ERR_PTR(-ESTALE);
88 inode = kernfs_get_inode(sb, kn);
89 kernfs_put(kn);
90 if (!inode)
91 return ERR_PTR(-ESTALE);
92
93 if (generation && inode->i_generation != generation) {
94 /* we didn't find the right inode.. */
95 iput(inode);
96 return ERR_PTR(-ESTALE);
97 }
98 return inode;
99}
100
101static struct dentry *kernfs_fh_to_dentry(struct super_block *sb, struct fid *fid,
102 int fh_len, int fh_type)
103{
104 return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
105 kernfs_fh_get_inode);
106}
107
108static struct dentry *kernfs_fh_to_parent(struct super_block *sb, struct fid *fid,
109 int fh_len, int fh_type)
110{
111 return generic_fh_to_parent(sb, fid, fh_len, fh_type,
112 kernfs_fh_get_inode);
113}
114
115static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
116{
117 struct kernfs_node *kn = kernfs_dentry_node(child);
118
119 return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
120}
121
122static const struct export_operations kernfs_export_ops = {
123 .fh_to_dentry = kernfs_fh_to_dentry,
124 .fh_to_parent = kernfs_fh_to_parent,
125 .get_parent = kernfs_get_parent_dentry,
126};
127
128/**
129 * kernfs_root_from_sb - determine kernfs_root associated with a super_block
130 * @sb: the super_block in question
131 *
132 * Return the kernfs_root associated with @sb. If @sb is not a kernfs one,
133 * %NULL is returned.
134 */
135struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
136{
137 if (sb->s_op == &kernfs_sops)
138 return kernfs_info(sb)->root;
139 return NULL;
140}
141
142/*
143 * find the next ancestor in the path down to @child, where @parent was the
144 * ancestor whose descendant we want to find.
145 *
146 * Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root
147 * node. If @parent is b, then we return the node for c.
148 * Passing in d as @parent is not ok.
149 */
150static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
151 struct kernfs_node *parent)
152{
153 if (child == parent) {
154 pr_crit_once("BUG in find_next_ancestor: called with parent == child");
155 return NULL;
156 }
157
158 while (child->parent != parent) {
159 if (!child->parent)
160 return NULL;
161 child = child->parent;
162 }
163
164 return child;
165}
166
167/**
168 * kernfs_node_dentry - get a dentry for the given kernfs_node
169 * @kn: kernfs_node for which a dentry is needed
170 * @sb: the kernfs super_block
171 */
172struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
173 struct super_block *sb)
174{
175 struct dentry *dentry;
176 struct kernfs_node *knparent = NULL;
177
178 BUG_ON(sb->s_op != &kernfs_sops);
179
180 dentry = dget(sb->s_root);
181
182 /* Check if this is the root kernfs_node */
183 if (!kn->parent)
184 return dentry;
185
186 knparent = find_next_ancestor(kn, NULL);
187 if (WARN_ON(!knparent)) {
188 dput(dentry);
189 return ERR_PTR(-EINVAL);
190 }
191
192 do {
193 struct dentry *dtmp;
194 struct kernfs_node *kntmp;
195
196 if (kn == knparent)
197 return dentry;
198 kntmp = find_next_ancestor(kn, knparent);
199 if (WARN_ON(!kntmp)) {
200 dput(dentry);
201 return ERR_PTR(-EINVAL);
202 }
203 dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
204 strlen(kntmp->name));
205 dput(dentry);
206 if (IS_ERR(dtmp))
207 return dtmp;
208 knparent = kntmp;
209 dentry = dtmp;
210 } while (true);
211}
212
213static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
214{
215 struct kernfs_super_info *info = kernfs_info(sb);
216 struct inode *inode;
217 struct dentry *root;
218
219 info->sb = sb;
220 /* Userspace would break if executables or devices appear on sysfs */
221 sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
222 sb->s_blocksize = PAGE_SIZE;
223 sb->s_blocksize_bits = PAGE_SHIFT;
224 sb->s_magic = kfc->magic;
225 sb->s_op = &kernfs_sops;
226 sb->s_xattr = kernfs_xattr_handlers;
227 if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
228 sb->s_export_op = &kernfs_export_ops;
229 sb->s_time_gran = 1;
230
231 /* sysfs dentries and inodes don't require IO to create */
232 sb->s_shrink.seeks = 0;
233
234 /* get root inode, initialize and unlock it */
235 mutex_lock(&kernfs_mutex);
236 inode = kernfs_get_inode(sb, info->root->kn);
237 mutex_unlock(&kernfs_mutex);
238 if (!inode) {
239 pr_debug("kernfs: could not get root inode\n");
240 return -ENOMEM;
241 }
242
243 /* instantiate and link root dentry */
244 root = d_make_root(inode);
245 if (!root) {
246 pr_debug("%s: could not get root dentry!\n", __func__);
247 return -ENOMEM;
248 }
249 sb->s_root = root;
250 sb->s_d_op = &kernfs_dops;
251 return 0;
252}
253
254static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
255{
256 struct kernfs_super_info *sb_info = kernfs_info(sb);
257 struct kernfs_super_info *info = fc->s_fs_info;
258
259 return sb_info->root == info->root && sb_info->ns == info->ns;
260}
261
262static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
263{
264 struct kernfs_fs_context *kfc = fc->fs_private;
265
266 kfc->ns_tag = NULL;
267 return set_anon_super_fc(sb, fc);
268}
269
270/**
271 * kernfs_super_ns - determine the namespace tag of a kernfs super_block
272 * @sb: super_block of interest
273 *
274 * Return the namespace tag associated with kernfs super_block @sb.
275 */
276const void *kernfs_super_ns(struct super_block *sb)
277{
278 struct kernfs_super_info *info = kernfs_info(sb);
279
280 return info->ns;
281}
282
283/**
284 * kernfs_get_tree - kernfs filesystem access/retrieval helper
285 * @fc: The filesystem context.
286 *
287 * This is to be called from each kernfs user's fs_context->ops->get_tree()
288 * implementation, which should set the specified ->@fs_type and ->@flags, and
289 * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
290 * respectively.
291 */
292int kernfs_get_tree(struct fs_context *fc)
293{
294 struct kernfs_fs_context *kfc = fc->fs_private;
295 struct super_block *sb;
296 struct kernfs_super_info *info;
297 int error;
298
299 info = kzalloc(sizeof(*info), GFP_KERNEL);
300 if (!info)
301 return -ENOMEM;
302
303 info->root = kfc->root;
304 info->ns = kfc->ns_tag;
305 INIT_LIST_HEAD(&info->node);
306
307 fc->s_fs_info = info;
308 sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
309 if (IS_ERR(sb))
310 return PTR_ERR(sb);
311
312 if (!sb->s_root) {
313 struct kernfs_super_info *info = kernfs_info(sb);
314
315 kfc->new_sb_created = true;
316
317 error = kernfs_fill_super(sb, kfc);
318 if (error) {
319 deactivate_locked_super(sb);
320 return error;
321 }
322 sb->s_flags |= SB_ACTIVE;
323
324 mutex_lock(&kernfs_mutex);
325 list_add(&info->node, &info->root->supers);
326 mutex_unlock(&kernfs_mutex);
327 }
328
329 fc->root = dget(sb->s_root);
330 return 0;
331}
332
333void kernfs_free_fs_context(struct fs_context *fc)
334{
335 /* Note that we don't deal with kfc->ns_tag here. */
336 kfree(fc->s_fs_info);
337 fc->s_fs_info = NULL;
338}
339
340/**
341 * kernfs_kill_sb - kill_sb for kernfs
342 * @sb: super_block being killed
343 *
344 * This can be used directly for file_system_type->kill_sb(). If a kernfs
345 * user needs extra cleanup, it can implement its own kill_sb() and call
346 * this function at the end.
347 */
348void kernfs_kill_sb(struct super_block *sb)
349{
350 struct kernfs_super_info *info = kernfs_info(sb);
351
352 mutex_lock(&kernfs_mutex);
353 list_del(&info->node);
354 mutex_unlock(&kernfs_mutex);
355
356 /*
357 * Remove the superblock from fs_supers/s_instances
358 * so we can't find it, before freeing kernfs_super_info.
359 */
360 kill_anon_super(sb);
361 kfree(info);
362}
363
364void __init kernfs_init(void)
365{
366
367 /*
368 * the slab is freed in RCU context, so kernfs_find_and_get_node_by_ino
369 * can access the slab lock free. This could introduce stale nodes,
370 * please see how kernfs_find_and_get_node_by_ino filters out stale
371 * nodes.
372 */
373 kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
374 sizeof(struct kernfs_node),
375 0,
376 SLAB_PANIC | SLAB_TYPESAFE_BY_RCU,
377 NULL);
378
379 /* Creates slab cache for kernfs inode attributes */
380 kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache",
381 sizeof(struct kernfs_iattrs),
382 0, SLAB_PANIC, NULL);
383}