1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * linux/fs/filesystems.c
4 *
5 * Copyright (C) 1991, 1992 Linus Torvalds
6 *
7 * table of configured filesystems
8 */
9
10 #include <linux/syscalls.h>
11 #include <linux/fs.h>
12 #include <linux/proc_fs.h>
13 #include <linux/seq_file.h>
14 #include <linux/kmod.h>
15 #include <linux/init.h>
16 #include <linux/module.h>
17 #include <linux/slab.h>
18 #include <linux/uaccess.h>
19 #include <linux/fs_parser.h>
20
21 /*
22 * Handling of filesystem drivers list.
23 * Rules:
24 * Inclusion to/removals from/scanning of list are protected by spinlock.
25 * During the unload module must call unregister_filesystem().
26 * We can access the fields of list element if:
27 * 1) spinlock is held or
28 * 2) we hold the reference to the module.
29 * The latter can be guaranteed by call of try_module_get(); if it
30 * returned 0 we must skip the element, otherwise we got the reference.
31 * Once the reference is obtained we can drop the spinlock.
32 */
33
34 static struct file_system_type *file_systems;
35 static DEFINE_RWLOCK(file_systems_lock);
36
37 /* WARNING: This can be used only if we _already_ own a reference */
38 struct file_system_type *get_filesystem(struct file_system_type *fs)
39 {
40 __module_get(fs->owner);
41 return fs;
42 }
43
44 void put_filesystem(struct file_system_type *fs)
45 {
46 module_put(fs->owner);
47 }
48
49 static struct file_system_type **find_filesystem(const char *name, unsigned len)
50 {
51 struct file_system_type **p;
52 for (p = &file_systems; *p; p = &(*p)->next)
53 if (strncmp((*p)->name, name, len) == 0 &&
54 !(*p)->name[len])
55 break;
56 return p;
57 }
58
59 /**
60 * register_filesystem - register a new filesystem
61 * @fs: the file system structure
62 *
63 * Adds the file system passed to the list of file systems the kernel
64 * is aware of for mount and other syscalls. Returns 0 on success,
65 * or a negative errno code on an error.
66 *
67 * The &struct file_system_type that is passed is linked into the kernel
68 * structures and must not be freed until the file system has been
69 * unregistered.
70 */
71
72 int register_filesystem(struct file_system_type * fs)
73 {
74 int res = 0;
75 struct file_system_type ** p;
76
77 if (fs->parameters &&
78 !fs_validate_description(fs->name, fs->parameters))
79 return -EINVAL;
80
81 BUG_ON(strchr(fs->name, '.'));
82 if (fs->next)
83 return -EBUSY;
84 write_lock(&file_systems_lock);
85 p = find_filesystem(fs->name, strlen(fs->name));
86 if (*p)
87 res = -EBUSY;
88 else
89 *p = fs;
90 write_unlock(&file_systems_lock);
91 return res;
92 }
93
94 EXPORT_SYMBOL(register_filesystem);
95
96 /**
97 * unregister_filesystem - unregister a file system
98 * @fs: filesystem to unregister
99 *
100 * Remove a file system that was previously successfully registered
101 * with the kernel. An error is returned if the file system is not found.
102 * Zero is returned on a success.
103 *
104 * Once this function has returned the &struct file_system_type structure
105 * may be freed or reused.
106 */
107
108 int unregister_filesystem(struct file_system_type * fs)
109 {
110 struct file_system_type ** tmp;
111
112 write_lock(&file_systems_lock);
113 tmp = &file_systems;
114 while (*tmp) {
115 if (fs == *tmp) {
116 *tmp = fs->next;
117 fs->next = NULL;
118 write_unlock(&file_systems_lock);
119 synchronize_rcu();
120 return 0;
121 }
122 tmp = &(*tmp)->next;
123 }
124 write_unlock(&file_systems_lock);
125
126 return -EINVAL;
127 }
128
129 EXPORT_SYMBOL(unregister_filesystem);
130
131 #ifdef CONFIG_SYSFS_SYSCALL
132 static int fs_index(const char __user * __name)
133 {
134 struct file_system_type * tmp;
135 struct filename *name;
136 int err, index;
137
138 name = getname(__name);
139 err = PTR_ERR(name);
140 if (IS_ERR(name))
141 return err;
142
143 err = -EINVAL;
144 read_lock(&file_systems_lock);
145 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
146 if (strcmp(tmp->name, name->name) == 0) {
147 err = index;
148 break;
149 }
150 }
151 read_unlock(&file_systems_lock);
152 putname(name);
153 return err;
154 }
155
156 static int fs_name(unsigned int index, char __user * buf)
157 {
158 struct file_system_type * tmp;
159 int len, res;
160
161 read_lock(&file_systems_lock);
162 for (tmp = file_systems; tmp; tmp = tmp->next, index--)
163 if (index <= 0 && try_module_get(tmp->owner))
164 break;
165 read_unlock(&file_systems_lock);
166 if (!tmp)
167 return -EINVAL;
168
169 /* OK, we got the reference, so we can safely block */
170 len = strlen(tmp->name) + 1;
171 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
172 put_filesystem(tmp);
173 return res;
174 }
175
176 static int fs_maxindex(void)
177 {
178 struct file_system_type * tmp;
179 int index;
180
181 read_lock(&file_systems_lock);
182 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
183 ;
184 read_unlock(&file_systems_lock);
185 return index;
186 }
187
188 /*
189 * Whee.. Weird sysv syscall.
190 */
191 SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
192 {
193 int retval = -EINVAL;
194
195 switch (option) {
196 case 1:
197 retval = fs_index((const char __user *) arg1);
198 break;
199
200 case 2:
201 retval = fs_name(arg1, (char __user *) arg2);
202 break;
203
204 case 3:
205 retval = fs_maxindex();
206 break;
207 }
208 return retval;
209 }
210 #endif
211
212 int __init list_bdev_fs_names(char *buf, size_t size)
213 {
214 struct file_system_type *p;
215 size_t len;
216 int count = 0;
217
218 read_lock(&file_systems_lock);
219 for (p = file_systems; p; p = p->next) {
220 if (!(p->fs_flags & FS_REQUIRES_DEV))
221 continue;
222 len = strlen(p->name) + 1;
223 if (len > size) {
224 pr_warn("%s: truncating file system list\n", __func__);
225 break;
226 }
227 memcpy(buf, p->name, len);
228 buf += len;
229 size -= len;
230 count++;
231 }
232 read_unlock(&file_systems_lock);
233 return count;
234 }
235
236 #ifdef CONFIG_PROC_FS
237 static int filesystems_proc_show(struct seq_file *m, void *v)
238 {
239 struct file_system_type * tmp;
240
241 read_lock(&file_systems_lock);
242 tmp = file_systems;
243 while (tmp) {
244 seq_printf(m, "%s\t%s\n",
245 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
246 tmp->name);
247 tmp = tmp->next;
248 }
249 read_unlock(&file_systems_lock);
250 return 0;
251 }
252
253 static int __init proc_filesystems_init(void)
254 {
255 proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
256 return 0;
257 }
258 module_init(proc_filesystems_init);
259 #endif
260
261 static struct file_system_type *__get_fs_type(const char *name, int len)
262 {
263 struct file_system_type *fs;
264
265 read_lock(&file_systems_lock);
266 fs = *(find_filesystem(name, len));
267 if (fs && !try_module_get(fs->owner))
268 fs = NULL;
269 read_unlock(&file_systems_lock);
270 return fs;
271 }
272
273 struct file_system_type *get_fs_type(const char *name)
274 {
275 struct file_system_type *fs;
276 const char *dot = strchr(name, '.');
277 int len = dot ? dot - name : strlen(name);
278
279 fs = __get_fs_type(name, len);
280 if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
281 fs = __get_fs_type(name, len);
282 if (!fs)
283 pr_warn_once("request_module fs-%.*s succeeded, but still no fs?\n",
284 len, name);
285 }
286
287 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
288 put_filesystem(fs);
289 fs = NULL;
290 }
291 return fs;
292 }
293
294 EXPORT_SYMBOL(get_fs_type);
295
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