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