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 :
24 908 : static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
25 : {
26 1816 : struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
27 908 : struct kernfs_syscall_ops *scops = root->syscall_ops;
28 :
29 908 : if (scops && scops->show_options)
30 577 : return scops->show_options(sf, root);
31 : return 0;
32 : }
33 :
34 903 : static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
35 : {
36 903 : struct kernfs_node *node = kernfs_dentry_node(dentry);
37 903 : struct kernfs_root *root = kernfs_root(node);
38 903 : struct kernfs_syscall_ops *scops = root->syscall_ops;
39 :
40 903 : if (scops && scops->show_path)
41 574 : return scops->show_path(sf, node, root);
42 :
43 329 : seq_dentry(sf, dentry, " \t\n\\");
44 329 : return 0;
45 : }
46 :
47 : const 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 0 : static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
57 : struct inode *parent)
58 : {
59 0 : struct kernfs_node *kn = inode->i_private;
60 :
61 0 : if (*max_len < 2) {
62 0 : *max_len = 2;
63 0 : return FILEID_INVALID;
64 : }
65 :
66 0 : *max_len = 2;
67 0 : *(u64 *)fh = kn->id;
68 0 : return FILEID_KERNFS;
69 : }
70 :
71 0 : static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
72 : struct fid *fid, int fh_len,
73 : int fh_type, bool get_parent)
74 : {
75 0 : struct kernfs_super_info *info = kernfs_info(sb);
76 0 : struct kernfs_node *kn;
77 0 : struct inode *inode;
78 0 : u64 id;
79 :
80 0 : if (fh_len < 2)
81 : return NULL;
82 :
83 0 : switch (fh_type) {
84 0 : case FILEID_KERNFS:
85 0 : id = *(u64 *)fid;
86 0 : break;
87 0 : case FILEID_INO32_GEN:
88 : case FILEID_INO32_GEN_PARENT:
89 : /*
90 : * blk_log_action() exposes "LOW32,HIGH32" pair without
91 : * type and userland can call us with generic fid
92 : * constructed from them. Combine it back to ID. See
93 : * blk_log_action().
94 : */
95 0 : id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
96 0 : break;
97 : default:
98 : return NULL;
99 : }
100 :
101 0 : kn = kernfs_find_and_get_node_by_id(info->root, id);
102 0 : if (!kn)
103 0 : return ERR_PTR(-ESTALE);
104 :
105 0 : if (get_parent) {
106 0 : struct kernfs_node *parent;
107 :
108 0 : parent = kernfs_get_parent(kn);
109 0 : kernfs_put(kn);
110 0 : kn = parent;
111 0 : if (!kn)
112 0 : return ERR_PTR(-ESTALE);
113 : }
114 :
115 0 : inode = kernfs_get_inode(sb, kn);
116 0 : kernfs_put(kn);
117 0 : if (!inode)
118 0 : return ERR_PTR(-ESTALE);
119 :
120 0 : return d_obtain_alias(inode);
121 : }
122 :
123 0 : static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
124 : struct fid *fid, int fh_len,
125 : int fh_type)
126 : {
127 0 : return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
128 : }
129 :
130 0 : static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
131 : struct fid *fid, int fh_len,
132 : int fh_type)
133 : {
134 0 : return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
135 : }
136 :
137 0 : static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
138 : {
139 0 : struct kernfs_node *kn = kernfs_dentry_node(child);
140 :
141 0 : return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
142 : }
143 :
144 : static const struct export_operations kernfs_export_ops = {
145 : .encode_fh = kernfs_encode_fh,
146 : .fh_to_dentry = kernfs_fh_to_dentry,
147 : .fh_to_parent = kernfs_fh_to_parent,
148 : .get_parent = kernfs_get_parent_dentry,
149 : };
150 :
151 : /**
152 : * kernfs_root_from_sb - determine kernfs_root associated with a super_block
153 : * @sb: the super_block in question
154 : *
155 : * Return the kernfs_root associated with @sb. If @sb is not a kernfs one,
156 : * %NULL is returned.
157 : */
158 0 : struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
159 : {
160 0 : if (sb->s_op == &kernfs_sops)
161 0 : return kernfs_info(sb)->root;
162 : return NULL;
163 : }
164 :
165 : /*
166 : * find the next ancestor in the path down to @child, where @parent was the
167 : * ancestor whose descendant we want to find.
168 : *
169 : * Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root
170 : * node. If @parent is b, then we return the node for c.
171 : * Passing in d as @parent is not ok.
172 : */
173 0 : static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
174 : struct kernfs_node *parent)
175 : {
176 0 : if (child == parent) {
177 0 : pr_crit_once("BUG in find_next_ancestor: called with parent == child");
178 0 : return NULL;
179 : }
180 :
181 0 : while (child->parent != parent) {
182 0 : if (!child->parent)
183 : return NULL;
184 : child = child->parent;
185 : }
186 :
187 : return child;
188 : }
189 :
190 : /**
191 : * kernfs_node_dentry - get a dentry for the given kernfs_node
192 : * @kn: kernfs_node for which a dentry is needed
193 : * @sb: the kernfs super_block
194 : */
195 0 : struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
196 : struct super_block *sb)
197 : {
198 0 : struct dentry *dentry;
199 0 : struct kernfs_node *knparent = NULL;
200 :
201 0 : BUG_ON(sb->s_op != &kernfs_sops);
202 :
203 0 : dentry = dget(sb->s_root);
204 :
205 : /* Check if this is the root kernfs_node */
206 0 : if (!kn->parent)
207 : return dentry;
208 :
209 0 : knparent = find_next_ancestor(kn, NULL);
210 0 : if (WARN_ON(!knparent)) {
211 0 : dput(dentry);
212 0 : return ERR_PTR(-EINVAL);
213 : }
214 :
215 0 : do {
216 0 : struct dentry *dtmp;
217 0 : struct kernfs_node *kntmp;
218 :
219 0 : if (kn == knparent)
220 0 : return dentry;
221 0 : kntmp = find_next_ancestor(kn, knparent);
222 0 : if (WARN_ON(!kntmp)) {
223 0 : dput(dentry);
224 0 : return ERR_PTR(-EINVAL);
225 : }
226 0 : dtmp = lookup_positive_unlocked(kntmp->name, dentry,
227 0 : strlen(kntmp->name));
228 0 : dput(dentry);
229 0 : if (IS_ERR(dtmp))
230 0 : return dtmp;
231 : knparent = kntmp;
232 : dentry = dtmp;
233 : } while (true);
234 : }
235 :
236 3 : static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
237 : {
238 3 : struct kernfs_super_info *info = kernfs_info(sb);
239 3 : struct inode *inode;
240 3 : struct dentry *root;
241 :
242 3 : info->sb = sb;
243 : /* Userspace would break if executables or devices appear on sysfs */
244 3 : sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
245 3 : sb->s_blocksize = PAGE_SIZE;
246 3 : sb->s_blocksize_bits = PAGE_SHIFT;
247 3 : sb->s_magic = kfc->magic;
248 3 : sb->s_op = &kernfs_sops;
249 3 : sb->s_xattr = kernfs_xattr_handlers;
250 3 : if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
251 2 : sb->s_export_op = &kernfs_export_ops;
252 3 : sb->s_time_gran = 1;
253 :
254 : /* sysfs dentries and inodes don't require IO to create */
255 3 : sb->s_shrink.seeks = 0;
256 :
257 : /* get root inode, initialize and unlock it */
258 3 : mutex_lock(&kernfs_mutex);
259 3 : inode = kernfs_get_inode(sb, info->root->kn);
260 3 : mutex_unlock(&kernfs_mutex);
261 3 : if (!inode) {
262 : pr_debug("kernfs: could not get root inode\n");
263 : return -ENOMEM;
264 : }
265 :
266 : /* instantiate and link root dentry */
267 3 : root = d_make_root(inode);
268 3 : if (!root) {
269 : pr_debug("%s: could not get root dentry!\n", __func__);
270 : return -ENOMEM;
271 : }
272 3 : sb->s_root = root;
273 3 : sb->s_d_op = &kernfs_dops;
274 3 : return 0;
275 : }
276 :
277 1 : static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
278 : {
279 1 : struct kernfs_super_info *sb_info = kernfs_info(sb);
280 1 : struct kernfs_super_info *info = fc->s_fs_info;
281 :
282 1 : return sb_info->root == info->root && sb_info->ns == info->ns;
283 : }
284 :
285 3 : static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
286 : {
287 3 : struct kernfs_fs_context *kfc = fc->fs_private;
288 :
289 3 : kfc->ns_tag = NULL;
290 3 : return set_anon_super_fc(sb, fc);
291 : }
292 :
293 : /**
294 : * kernfs_super_ns - determine the namespace tag of a kernfs super_block
295 : * @sb: super_block of interest
296 : *
297 : * Return the namespace tag associated with kernfs super_block @sb.
298 : */
299 0 : const void *kernfs_super_ns(struct super_block *sb)
300 : {
301 0 : struct kernfs_super_info *info = kernfs_info(sb);
302 :
303 0 : return info->ns;
304 : }
305 :
306 : /**
307 : * kernfs_get_tree - kernfs filesystem access/retrieval helper
308 : * @fc: The filesystem context.
309 : *
310 : * This is to be called from each kernfs user's fs_context->ops->get_tree()
311 : * implementation, which should set the specified ->@fs_type and ->@flags, and
312 : * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
313 : * respectively.
314 : */
315 4 : int kernfs_get_tree(struct fs_context *fc)
316 : {
317 4 : struct kernfs_fs_context *kfc = fc->fs_private;
318 4 : struct super_block *sb;
319 4 : struct kernfs_super_info *info;
320 4 : int error;
321 :
322 4 : info = kzalloc(sizeof(*info), GFP_KERNEL);
323 4 : if (!info)
324 : return -ENOMEM;
325 :
326 4 : info->root = kfc->root;
327 4 : info->ns = kfc->ns_tag;
328 4 : INIT_LIST_HEAD(&info->node);
329 :
330 4 : fc->s_fs_info = info;
331 4 : sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
332 4 : if (IS_ERR(sb))
333 0 : return PTR_ERR(sb);
334 :
335 4 : if (!sb->s_root) {
336 3 : struct kernfs_super_info *info = kernfs_info(sb);
337 :
338 3 : kfc->new_sb_created = true;
339 :
340 3 : error = kernfs_fill_super(sb, kfc);
341 3 : if (error) {
342 0 : deactivate_locked_super(sb);
343 0 : return error;
344 : }
345 3 : sb->s_flags |= SB_ACTIVE;
346 :
347 3 : mutex_lock(&kernfs_mutex);
348 3 : list_add(&info->node, &info->root->supers);
349 3 : mutex_unlock(&kernfs_mutex);
350 : }
351 :
352 4 : fc->root = dget(sb->s_root);
353 4 : return 0;
354 : }
355 :
356 4 : void kernfs_free_fs_context(struct fs_context *fc)
357 : {
358 : /* Note that we don't deal with kfc->ns_tag here. */
359 4 : kfree(fc->s_fs_info);
360 4 : fc->s_fs_info = NULL;
361 4 : }
362 :
363 : /**
364 : * kernfs_kill_sb - kill_sb for kernfs
365 : * @sb: super_block being killed
366 : *
367 : * This can be used directly for file_system_type->kill_sb(). If a kernfs
368 : * user needs extra cleanup, it can implement its own kill_sb() and call
369 : * this function at the end.
370 : */
371 0 : void kernfs_kill_sb(struct super_block *sb)
372 : {
373 0 : struct kernfs_super_info *info = kernfs_info(sb);
374 :
375 0 : mutex_lock(&kernfs_mutex);
376 0 : list_del(&info->node);
377 0 : mutex_unlock(&kernfs_mutex);
378 :
379 : /*
380 : * Remove the superblock from fs_supers/s_instances
381 : * so we can't find it, before freeing kernfs_super_info.
382 : */
383 0 : kill_anon_super(sb);
384 0 : kfree(info);
385 0 : }
386 :
387 1 : void __init kernfs_init(void)
388 : {
389 1 : kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
390 : sizeof(struct kernfs_node),
391 : 0, SLAB_PANIC, NULL);
392 :
393 : /* Creates slab cache for kernfs inode attributes */
394 1 : kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache",
395 : sizeof(struct kernfs_iattrs),
396 : 0, SLAB_PANIC, NULL);
397 1 : }
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