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
kernfs_sop_show_options(struct seq_file * sf,struct dentry * dentry)24 static 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
kernfs_sop_show_path(struct seq_file * sf,struct dentry * dentry)34 static 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
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
kernfs_encode_fh(struct inode * inode,__u32 * fh,int * max_len,struct inode * parent)56 static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
57 struct inode *parent)
58 {
59 struct kernfs_node *kn = inode->i_private;
60
61 if (*max_len < 2) {
62 *max_len = 2;
63 return FILEID_INVALID;
64 }
65
66 *max_len = 2;
67 *(u64 *)fh = kn->id;
68 return FILEID_KERNFS;
69 }
70
__kernfs_fh_to_dentry(struct super_block * sb,struct fid * fid,int fh_len,int fh_type,bool get_parent)71 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 struct kernfs_super_info *info = kernfs_info(sb);
76 struct kernfs_node *kn;
77 struct inode *inode;
78 u64 id;
79
80 if (fh_len < 2)
81 return NULL;
82
83 switch (fh_type) {
84 case FILEID_KERNFS:
85 id = *(u64 *)fid;
86 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 id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
96 break;
97 default:
98 return NULL;
99 }
100
101 kn = kernfs_find_and_get_node_by_id(info->root, id);
102 if (!kn)
103 return ERR_PTR(-ESTALE);
104
105 if (get_parent) {
106 struct kernfs_node *parent;
107
108 parent = kernfs_get_parent(kn);
109 kernfs_put(kn);
110 kn = parent;
111 if (!kn)
112 return ERR_PTR(-ESTALE);
113 }
114
115 inode = kernfs_get_inode(sb, kn);
116 kernfs_put(kn);
117 if (!inode)
118 return ERR_PTR(-ESTALE);
119
120 return d_obtain_alias(inode);
121 }
122
kernfs_fh_to_dentry(struct super_block * sb,struct fid * fid,int fh_len,int fh_type)123 static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
124 struct fid *fid, int fh_len,
125 int fh_type)
126 {
127 return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
128 }
129
kernfs_fh_to_parent(struct super_block * sb,struct fid * fid,int fh_len,int fh_type)130 static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
131 struct fid *fid, int fh_len,
132 int fh_type)
133 {
134 return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
135 }
136
kernfs_get_parent_dentry(struct dentry * child)137 static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
138 {
139 struct kernfs_node *kn = kernfs_dentry_node(child);
140
141 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 */
kernfs_root_from_sb(struct super_block * sb)158 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
159 {
160 if (sb->s_op == &kernfs_sops)
161 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 */
find_next_ancestor(struct kernfs_node * child,struct kernfs_node * parent)173 static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
174 struct kernfs_node *parent)
175 {
176 if (child == parent) {
177 pr_crit_once("BUG in find_next_ancestor: called with parent == child");
178 return NULL;
179 }
180
181 while (child->parent != parent) {
182 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 */
kernfs_node_dentry(struct kernfs_node * kn,struct super_block * sb)195 struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
196 struct super_block *sb)
197 {
198 struct dentry *dentry;
199 struct kernfs_node *knparent = NULL;
200
201 BUG_ON(sb->s_op != &kernfs_sops);
202
203 dentry = dget(sb->s_root);
204
205 /* Check if this is the root kernfs_node */
206 if (!kn->parent)
207 return dentry;
208
209 knparent = find_next_ancestor(kn, NULL);
210 if (WARN_ON(!knparent)) {
211 dput(dentry);
212 return ERR_PTR(-EINVAL);
213 }
214
215 do {
216 struct dentry *dtmp;
217 struct kernfs_node *kntmp;
218
219 if (kn == knparent)
220 return dentry;
221 kntmp = find_next_ancestor(kn, knparent);
222 if (WARN_ON(!kntmp)) {
223 dput(dentry);
224 return ERR_PTR(-EINVAL);
225 }
226 dtmp = lookup_positive_unlocked(kntmp->name, dentry,
227 strlen(kntmp->name));
228 dput(dentry);
229 if (IS_ERR(dtmp))
230 return dtmp;
231 knparent = kntmp;
232 dentry = dtmp;
233 } while (true);
234 }
235
kernfs_fill_super(struct super_block * sb,struct kernfs_fs_context * kfc)236 static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
237 {
238 struct kernfs_super_info *info = kernfs_info(sb);
239 struct inode *inode;
240 struct dentry *root;
241
242 info->sb = sb;
243 /* Userspace would break if executables or devices appear on sysfs */
244 sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
245 sb->s_blocksize = PAGE_SIZE;
246 sb->s_blocksize_bits = PAGE_SHIFT;
247 sb->s_magic = kfc->magic;
248 sb->s_op = &kernfs_sops;
249 sb->s_xattr = kernfs_xattr_handlers;
250 if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
251 sb->s_export_op = &kernfs_export_ops;
252 sb->s_time_gran = 1;
253
254 /* sysfs dentries and inodes don't require IO to create */
255 sb->s_shrink.seeks = 0;
256
257 /* get root inode, initialize and unlock it */
258 mutex_lock(&kernfs_mutex);
259 inode = kernfs_get_inode(sb, info->root->kn);
260 mutex_unlock(&kernfs_mutex);
261 if (!inode) {
262 pr_debug("kernfs: could not get root inode\n");
263 return -ENOMEM;
264 }
265
266 /* instantiate and link root dentry */
267 root = d_make_root(inode);
268 if (!root) {
269 pr_debug("%s: could not get root dentry!\n", __func__);
270 return -ENOMEM;
271 }
272 sb->s_root = root;
273 sb->s_d_op = &kernfs_dops;
274 return 0;
275 }
276
kernfs_test_super(struct super_block * sb,struct fs_context * fc)277 static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
278 {
279 struct kernfs_super_info *sb_info = kernfs_info(sb);
280 struct kernfs_super_info *info = fc->s_fs_info;
281
282 return sb_info->root == info->root && sb_info->ns == info->ns;
283 }
284
kernfs_set_super(struct super_block * sb,struct fs_context * fc)285 static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
286 {
287 struct kernfs_fs_context *kfc = fc->fs_private;
288
289 kfc->ns_tag = NULL;
290 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 */
kernfs_super_ns(struct super_block * sb)299 const void *kernfs_super_ns(struct super_block *sb)
300 {
301 struct kernfs_super_info *info = kernfs_info(sb);
302
303 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 */
kernfs_get_tree(struct fs_context * fc)315 int kernfs_get_tree(struct fs_context *fc)
316 {
317 struct kernfs_fs_context *kfc = fc->fs_private;
318 struct super_block *sb;
319 struct kernfs_super_info *info;
320 int error;
321
322 info = kzalloc(sizeof(*info), GFP_KERNEL);
323 if (!info)
324 return -ENOMEM;
325
326 info->root = kfc->root;
327 info->ns = kfc->ns_tag;
328 INIT_LIST_HEAD(&info->node);
329
330 fc->s_fs_info = info;
331 sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
332 if (IS_ERR(sb))
333 return PTR_ERR(sb);
334
335 if (!sb->s_root) {
336 struct kernfs_super_info *info = kernfs_info(sb);
337
338 kfc->new_sb_created = true;
339
340 error = kernfs_fill_super(sb, kfc);
341 if (error) {
342 deactivate_locked_super(sb);
343 return error;
344 }
345 sb->s_flags |= SB_ACTIVE;
346
347 mutex_lock(&kernfs_mutex);
348 list_add(&info->node, &info->root->supers);
349 mutex_unlock(&kernfs_mutex);
350 }
351
352 fc->root = dget(sb->s_root);
353 return 0;
354 }
355
kernfs_free_fs_context(struct fs_context * fc)356 void kernfs_free_fs_context(struct fs_context *fc)
357 {
358 /* Note that we don't deal with kfc->ns_tag here. */
359 kfree(fc->s_fs_info);
360 fc->s_fs_info = NULL;
361 }
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 */
kernfs_kill_sb(struct super_block * sb)371 void kernfs_kill_sb(struct super_block *sb)
372 {
373 struct kernfs_super_info *info = kernfs_info(sb);
374
375 mutex_lock(&kernfs_mutex);
376 list_del(&info->node);
377 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 kill_anon_super(sb);
384 kfree(info);
385 }
386
kernfs_init(void)387 void __init kernfs_init(void)
388 {
389 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 kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache",
395 sizeof(struct kernfs_iattrs),
396 0, SLAB_PANIC, NULL);
397 }
398