Line data Source code
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 :
22 : struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;
23 : struct kernfs_global_locks *kernfs_locks;
24 :
25 0 : static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
26 : {
27 0 : struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
28 0 : struct kernfs_syscall_ops *scops = root->syscall_ops;
29 :
30 0 : if (scops && scops->show_options)
31 0 : return scops->show_options(sf, root);
32 : return 0;
33 : }
34 :
35 0 : static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
36 : {
37 0 : struct kernfs_node *node = kernfs_dentry_node(dentry);
38 0 : struct kernfs_root *root = kernfs_root(node);
39 0 : struct kernfs_syscall_ops *scops = root->syscall_ops;
40 :
41 0 : if (scops && scops->show_path)
42 0 : return scops->show_path(sf, node, root);
43 :
44 0 : seq_dentry(sf, dentry, " \t\n\\");
45 0 : return 0;
46 : }
47 :
48 : const struct super_operations kernfs_sops = {
49 : .statfs = simple_statfs,
50 : .drop_inode = generic_delete_inode,
51 : .evict_inode = kernfs_evict_inode,
52 :
53 : .show_options = kernfs_sop_show_options,
54 : .show_path = kernfs_sop_show_path,
55 : };
56 :
57 0 : static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
58 : struct inode *parent)
59 : {
60 0 : struct kernfs_node *kn = inode->i_private;
61 :
62 0 : if (*max_len < 2) {
63 0 : *max_len = 2;
64 0 : return FILEID_INVALID;
65 : }
66 :
67 0 : *max_len = 2;
68 0 : *(u64 *)fh = kn->id;
69 0 : return FILEID_KERNFS;
70 : }
71 :
72 0 : static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
73 : struct fid *fid, int fh_len,
74 : int fh_type, bool get_parent)
75 : {
76 0 : struct kernfs_super_info *info = kernfs_info(sb);
77 : struct kernfs_node *kn;
78 : struct inode *inode;
79 : u64 id;
80 :
81 0 : if (fh_len < 2)
82 : return NULL;
83 :
84 0 : switch (fh_type) {
85 : case FILEID_KERNFS:
86 0 : id = *(u64 *)fid;
87 0 : break;
88 : case FILEID_INO32_GEN:
89 : case FILEID_INO32_GEN_PARENT:
90 : /*
91 : * blk_log_action() exposes "LOW32,HIGH32" pair without
92 : * type and userland can call us with generic fid
93 : * constructed from them. Combine it back to ID. See
94 : * blk_log_action().
95 : */
96 0 : id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
97 0 : break;
98 : default:
99 : return NULL;
100 : }
101 :
102 0 : kn = kernfs_find_and_get_node_by_id(info->root, id);
103 0 : if (!kn)
104 : return ERR_PTR(-ESTALE);
105 :
106 0 : if (get_parent) {
107 : struct kernfs_node *parent;
108 :
109 0 : parent = kernfs_get_parent(kn);
110 0 : kernfs_put(kn);
111 0 : kn = parent;
112 0 : if (!kn)
113 : return ERR_PTR(-ESTALE);
114 : }
115 :
116 0 : inode = kernfs_get_inode(sb, kn);
117 0 : kernfs_put(kn);
118 0 : if (!inode)
119 : return ERR_PTR(-ESTALE);
120 :
121 0 : return d_obtain_alias(inode);
122 : }
123 :
124 0 : static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
125 : struct fid *fid, int fh_len,
126 : int fh_type)
127 : {
128 0 : return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
129 : }
130 :
131 0 : static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
132 : struct fid *fid, int fh_len,
133 : int fh_type)
134 : {
135 0 : return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
136 : }
137 :
138 0 : static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
139 : {
140 0 : struct kernfs_node *kn = kernfs_dentry_node(child);
141 :
142 0 : return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
143 : }
144 :
145 : static const struct export_operations kernfs_export_ops = {
146 : .encode_fh = kernfs_encode_fh,
147 : .fh_to_dentry = kernfs_fh_to_dentry,
148 : .fh_to_parent = kernfs_fh_to_parent,
149 : .get_parent = kernfs_get_parent_dentry,
150 : };
151 :
152 : /**
153 : * kernfs_root_from_sb - determine kernfs_root associated with a super_block
154 : * @sb: the super_block in question
155 : *
156 : * Return: the kernfs_root associated with @sb. If @sb is not a kernfs one,
157 : * %NULL is returned.
158 : */
159 0 : struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
160 : {
161 0 : if (sb->s_op == &kernfs_sops)
162 0 : return kernfs_info(sb)->root;
163 : return NULL;
164 : }
165 :
166 : /*
167 : * find the next ancestor in the path down to @child, where @parent was the
168 : * ancestor whose descendant we want to find.
169 : *
170 : * Say the path is /a/b/c/d. @child is d, @parent is %NULL. We return the root
171 : * node. If @parent is b, then we return the node for c.
172 : * Passing in d as @parent is not ok.
173 : */
174 0 : static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
175 : struct kernfs_node *parent)
176 : {
177 0 : if (child == parent) {
178 0 : pr_crit_once("BUG in find_next_ancestor: called with parent == child");
179 : return NULL;
180 : }
181 :
182 0 : while (child->parent != parent) {
183 0 : if (!child->parent)
184 : return NULL;
185 : child = child->parent;
186 : }
187 :
188 : return child;
189 : }
190 :
191 : /**
192 : * kernfs_node_dentry - get a dentry for the given kernfs_node
193 : * @kn: kernfs_node for which a dentry is needed
194 : * @sb: the kernfs super_block
195 : *
196 : * Return: the dentry pointer
197 : */
198 0 : struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
199 : struct super_block *sb)
200 : {
201 : struct dentry *dentry;
202 0 : struct kernfs_node *knparent = NULL;
203 :
204 0 : BUG_ON(sb->s_op != &kernfs_sops);
205 :
206 0 : dentry = dget(sb->s_root);
207 :
208 : /* Check if this is the root kernfs_node */
209 0 : if (!kn->parent)
210 : return dentry;
211 :
212 0 : knparent = find_next_ancestor(kn, NULL);
213 0 : if (WARN_ON(!knparent)) {
214 0 : dput(dentry);
215 0 : return ERR_PTR(-EINVAL);
216 : }
217 :
218 : do {
219 : struct dentry *dtmp;
220 : struct kernfs_node *kntmp;
221 :
222 0 : if (kn == knparent)
223 : return dentry;
224 0 : kntmp = find_next_ancestor(kn, knparent);
225 0 : if (WARN_ON(!kntmp)) {
226 0 : dput(dentry);
227 0 : return ERR_PTR(-EINVAL);
228 : }
229 0 : dtmp = lookup_positive_unlocked(kntmp->name, dentry,
230 0 : strlen(kntmp->name));
231 0 : dput(dentry);
232 0 : if (IS_ERR(dtmp))
233 : return dtmp;
234 : knparent = kntmp;
235 : dentry = dtmp;
236 : } while (true);
237 : }
238 :
239 0 : static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
240 : {
241 0 : struct kernfs_super_info *info = kernfs_info(sb);
242 0 : struct kernfs_root *kf_root = kfc->root;
243 : struct inode *inode;
244 : struct dentry *root;
245 :
246 0 : info->sb = sb;
247 : /* Userspace would break if executables or devices appear on sysfs */
248 0 : sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
249 0 : sb->s_blocksize = PAGE_SIZE;
250 0 : sb->s_blocksize_bits = PAGE_SHIFT;
251 0 : sb->s_magic = kfc->magic;
252 0 : sb->s_op = &kernfs_sops;
253 0 : sb->s_xattr = kernfs_xattr_handlers;
254 0 : if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
255 0 : sb->s_export_op = &kernfs_export_ops;
256 0 : sb->s_time_gran = 1;
257 :
258 : /* sysfs dentries and inodes don't require IO to create */
259 0 : sb->s_shrink.seeks = 0;
260 :
261 : /* get root inode, initialize and unlock it */
262 0 : down_read(&kf_root->kernfs_rwsem);
263 0 : inode = kernfs_get_inode(sb, info->root->kn);
264 0 : up_read(&kf_root->kernfs_rwsem);
265 0 : if (!inode) {
266 : pr_debug("kernfs: could not get root inode\n");
267 : return -ENOMEM;
268 : }
269 :
270 : /* instantiate and link root dentry */
271 0 : root = d_make_root(inode);
272 0 : if (!root) {
273 : pr_debug("%s: could not get root dentry!\n", __func__);
274 : return -ENOMEM;
275 : }
276 0 : sb->s_root = root;
277 0 : sb->s_d_op = &kernfs_dops;
278 : return 0;
279 : }
280 :
281 0 : static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
282 : {
283 0 : struct kernfs_super_info *sb_info = kernfs_info(sb);
284 0 : struct kernfs_super_info *info = fc->s_fs_info;
285 :
286 0 : return sb_info->root == info->root && sb_info->ns == info->ns;
287 : }
288 :
289 0 : static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
290 : {
291 0 : struct kernfs_fs_context *kfc = fc->fs_private;
292 :
293 0 : kfc->ns_tag = NULL;
294 0 : return set_anon_super_fc(sb, fc);
295 : }
296 :
297 : /**
298 : * kernfs_super_ns - determine the namespace tag of a kernfs super_block
299 : * @sb: super_block of interest
300 : *
301 : * Return: the namespace tag associated with kernfs super_block @sb.
302 : */
303 0 : const void *kernfs_super_ns(struct super_block *sb)
304 : {
305 0 : struct kernfs_super_info *info = kernfs_info(sb);
306 :
307 0 : return info->ns;
308 : }
309 :
310 : /**
311 : * kernfs_get_tree - kernfs filesystem access/retrieval helper
312 : * @fc: The filesystem context.
313 : *
314 : * This is to be called from each kernfs user's fs_context->ops->get_tree()
315 : * implementation, which should set the specified ->@fs_type and ->@flags, and
316 : * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
317 : * respectively.
318 : *
319 : * Return: %0 on success, -errno on failure.
320 : */
321 0 : int kernfs_get_tree(struct fs_context *fc)
322 : {
323 0 : struct kernfs_fs_context *kfc = fc->fs_private;
324 : struct super_block *sb;
325 : struct kernfs_super_info *info;
326 : int error;
327 :
328 0 : info = kzalloc(sizeof(*info), GFP_KERNEL);
329 0 : if (!info)
330 : return -ENOMEM;
331 :
332 0 : info->root = kfc->root;
333 0 : info->ns = kfc->ns_tag;
334 0 : INIT_LIST_HEAD(&info->node);
335 :
336 0 : fc->s_fs_info = info;
337 0 : sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
338 0 : if (IS_ERR(sb))
339 0 : return PTR_ERR(sb);
340 :
341 0 : if (!sb->s_root) {
342 0 : struct kernfs_super_info *info = kernfs_info(sb);
343 0 : struct kernfs_root *root = kfc->root;
344 :
345 0 : kfc->new_sb_created = true;
346 :
347 0 : error = kernfs_fill_super(sb, kfc);
348 0 : if (error) {
349 0 : deactivate_locked_super(sb);
350 0 : return error;
351 : }
352 0 : sb->s_flags |= SB_ACTIVE;
353 :
354 0 : down_write(&root->kernfs_rwsem);
355 0 : list_add(&info->node, &info->root->supers);
356 0 : up_write(&root->kernfs_rwsem);
357 : }
358 :
359 0 : fc->root = dget(sb->s_root);
360 0 : return 0;
361 : }
362 :
363 0 : void kernfs_free_fs_context(struct fs_context *fc)
364 : {
365 : /* Note that we don't deal with kfc->ns_tag here. */
366 0 : kfree(fc->s_fs_info);
367 0 : fc->s_fs_info = NULL;
368 0 : }
369 :
370 : /**
371 : * kernfs_kill_sb - kill_sb for kernfs
372 : * @sb: super_block being killed
373 : *
374 : * This can be used directly for file_system_type->kill_sb(). If a kernfs
375 : * user needs extra cleanup, it can implement its own kill_sb() and call
376 : * this function at the end.
377 : */
378 0 : void kernfs_kill_sb(struct super_block *sb)
379 : {
380 0 : struct kernfs_super_info *info = kernfs_info(sb);
381 0 : struct kernfs_root *root = info->root;
382 :
383 0 : down_write(&root->kernfs_rwsem);
384 0 : list_del(&info->node);
385 0 : up_write(&root->kernfs_rwsem);
386 :
387 : /*
388 : * Remove the superblock from fs_supers/s_instances
389 : * so we can't find it, before freeing kernfs_super_info.
390 : */
391 0 : kill_anon_super(sb);
392 0 : kfree(info);
393 0 : }
394 :
395 1 : static void __init kernfs_mutex_init(void)
396 : {
397 : int count;
398 :
399 3 : for (count = 0; count < NR_KERNFS_LOCKS; count++)
400 2 : mutex_init(&kernfs_locks->open_file_mutex[count]);
401 1 : }
402 :
403 1 : static void __init kernfs_lock_init(void)
404 : {
405 1 : kernfs_locks = kmalloc(sizeof(struct kernfs_global_locks), GFP_KERNEL);
406 1 : WARN_ON(!kernfs_locks);
407 :
408 1 : kernfs_mutex_init();
409 1 : }
410 :
411 1 : void __init kernfs_init(void)
412 : {
413 1 : kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
414 : sizeof(struct kernfs_node),
415 : 0, SLAB_PANIC, NULL);
416 :
417 : /* Creates slab cache for kernfs inode attributes */
418 1 : kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache",
419 : sizeof(struct kernfs_iattrs),
420 : 0, SLAB_PANIC, NULL);
421 :
422 1 : kernfs_lock_init();
423 1 : }
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