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