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 0 : static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
25 : {
26 0 : struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
27 0 : struct kernfs_syscall_ops *scops = root->syscall_ops;
28 :
29 0 : if (scops && scops->show_options)
30 0 : return scops->show_options(sf, root);
31 : return 0;
32 : }
33 :
34 0 : static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
35 : {
36 0 : struct kernfs_node *node = kernfs_dentry_node(dentry);
37 0 : struct kernfs_root *root = kernfs_root(node);
38 0 : struct kernfs_syscall_ops *scops = root->syscall_ops;
39 :
40 0 : if (scops && scops->show_path)
41 0 : return scops->show_path(sf, node, root);
42 :
43 0 : seq_dentry(sf, dentry, " \t\n\\");
44 0 : 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 : struct kernfs_node *kn;
77 : struct inode *inode;
78 : u64 id;
79 :
80 0 : if (fh_len < 2)
81 : return NULL;
82 :
83 0 : switch (fh_type) {
84 : case FILEID_KERNFS:
85 0 : id = *(u64 *)fid;
86 0 : break;
87 : 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 : return ERR_PTR(-ESTALE);
104 :
105 0 : if (get_parent) {
106 : 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 : return ERR_PTR(-ESTALE);
113 : }
114 :
115 0 : inode = kernfs_get_inode(sb, kn);
116 0 : kernfs_put(kn);
117 0 : if (!inode)
118 : 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 : 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 : 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 : do {
216 : struct dentry *dtmp;
217 : struct kernfs_node *kntmp;
218 :
219 0 : if (kn == knparent)
220 : 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 : return dtmp;
231 : knparent = kntmp;
232 : dentry = dtmp;
233 : } while (true);
234 : }
235 :
236 0 : static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
237 : {
238 0 : struct kernfs_super_info *info = kernfs_info(sb);
239 0 : struct kernfs_root *kf_root = kfc->root;
240 : struct inode *inode;
241 : struct dentry *root;
242 :
243 0 : info->sb = sb;
244 : /* Userspace would break if executables or devices appear on sysfs */
245 0 : sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
246 0 : sb->s_blocksize = PAGE_SIZE;
247 0 : sb->s_blocksize_bits = PAGE_SHIFT;
248 0 : sb->s_magic = kfc->magic;
249 0 : sb->s_op = &kernfs_sops;
250 0 : sb->s_xattr = kernfs_xattr_handlers;
251 0 : if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
252 0 : sb->s_export_op = &kernfs_export_ops;
253 0 : sb->s_time_gran = 1;
254 :
255 : /* sysfs dentries and inodes don't require IO to create */
256 0 : sb->s_shrink.seeks = 0;
257 :
258 : /* get root inode, initialize and unlock it */
259 0 : down_read(&kf_root->kernfs_rwsem);
260 0 : inode = kernfs_get_inode(sb, info->root->kn);
261 0 : up_read(&kf_root->kernfs_rwsem);
262 0 : if (!inode) {
263 : pr_debug("kernfs: could not get root inode\n");
264 : return -ENOMEM;
265 : }
266 :
267 : /* instantiate and link root dentry */
268 0 : root = d_make_root(inode);
269 0 : if (!root) {
270 : pr_debug("%s: could not get root dentry!\n", __func__);
271 : return -ENOMEM;
272 : }
273 0 : sb->s_root = root;
274 0 : sb->s_d_op = &kernfs_dops;
275 : return 0;
276 : }
277 :
278 0 : static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
279 : {
280 0 : struct kernfs_super_info *sb_info = kernfs_info(sb);
281 0 : struct kernfs_super_info *info = fc->s_fs_info;
282 :
283 0 : return sb_info->root == info->root && sb_info->ns == info->ns;
284 : }
285 :
286 0 : static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
287 : {
288 0 : struct kernfs_fs_context *kfc = fc->fs_private;
289 :
290 0 : kfc->ns_tag = NULL;
291 0 : return set_anon_super_fc(sb, fc);
292 : }
293 :
294 : /**
295 : * kernfs_super_ns - determine the namespace tag of a kernfs super_block
296 : * @sb: super_block of interest
297 : *
298 : * Return the namespace tag associated with kernfs super_block @sb.
299 : */
300 0 : const void *kernfs_super_ns(struct super_block *sb)
301 : {
302 0 : struct kernfs_super_info *info = kernfs_info(sb);
303 :
304 0 : return info->ns;
305 : }
306 :
307 : /**
308 : * kernfs_get_tree - kernfs filesystem access/retrieval helper
309 : * @fc: The filesystem context.
310 : *
311 : * This is to be called from each kernfs user's fs_context->ops->get_tree()
312 : * implementation, which should set the specified ->@fs_type and ->@flags, and
313 : * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
314 : * respectively.
315 : */
316 0 : int kernfs_get_tree(struct fs_context *fc)
317 : {
318 0 : struct kernfs_fs_context *kfc = fc->fs_private;
319 : struct super_block *sb;
320 : struct kernfs_super_info *info;
321 : int error;
322 :
323 0 : info = kzalloc(sizeof(*info), GFP_KERNEL);
324 0 : if (!info)
325 : return -ENOMEM;
326 :
327 0 : info->root = kfc->root;
328 0 : info->ns = kfc->ns_tag;
329 0 : INIT_LIST_HEAD(&info->node);
330 :
331 0 : fc->s_fs_info = info;
332 0 : sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
333 0 : if (IS_ERR(sb))
334 0 : return PTR_ERR(sb);
335 :
336 0 : if (!sb->s_root) {
337 0 : struct kernfs_super_info *info = kernfs_info(sb);
338 0 : struct kernfs_root *root = kfc->root;
339 :
340 0 : kfc->new_sb_created = true;
341 :
342 0 : error = kernfs_fill_super(sb, kfc);
343 0 : if (error) {
344 0 : deactivate_locked_super(sb);
345 0 : return error;
346 : }
347 0 : sb->s_flags |= SB_ACTIVE;
348 :
349 0 : down_write(&root->kernfs_rwsem);
350 0 : list_add(&info->node, &info->root->supers);
351 0 : up_write(&root->kernfs_rwsem);
352 : }
353 :
354 0 : fc->root = dget(sb->s_root);
355 0 : return 0;
356 : }
357 :
358 0 : void kernfs_free_fs_context(struct fs_context *fc)
359 : {
360 : /* Note that we don't deal with kfc->ns_tag here. */
361 0 : kfree(fc->s_fs_info);
362 0 : fc->s_fs_info = NULL;
363 0 : }
364 :
365 : /**
366 : * kernfs_kill_sb - kill_sb for kernfs
367 : * @sb: super_block being killed
368 : *
369 : * This can be used directly for file_system_type->kill_sb(). If a kernfs
370 : * user needs extra cleanup, it can implement its own kill_sb() and call
371 : * this function at the end.
372 : */
373 0 : void kernfs_kill_sb(struct super_block *sb)
374 : {
375 0 : struct kernfs_super_info *info = kernfs_info(sb);
376 0 : struct kernfs_root *root = info->root;
377 :
378 0 : down_write(&root->kernfs_rwsem);
379 0 : list_del(&info->node);
380 0 : up_write(&root->kernfs_rwsem);
381 :
382 : /*
383 : * Remove the superblock from fs_supers/s_instances
384 : * so we can't find it, before freeing kernfs_super_info.
385 : */
386 0 : kill_anon_super(sb);
387 0 : kfree(info);
388 0 : }
389 :
390 1 : void __init kernfs_init(void)
391 : {
392 1 : kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
393 : sizeof(struct kernfs_node),
394 : 0, SLAB_PANIC, NULL);
395 :
396 : /* Creates slab cache for kernfs inode attributes */
397 1 : kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache",
398 : sizeof(struct kernfs_iattrs),
399 : 0, SLAB_PANIC, NULL);
400 1 : }
|
