Line data Source code
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 30 : struct file_system_type *get_filesystem(struct file_system_type *fs)
39 : {
40 30 : __module_get(fs->owner);
41 30 : return fs;
42 : }
43 :
44 21 : void put_filesystem(struct file_system_type *fs)
45 : {
46 21 : module_put(fs->owner);
47 21 : }
48 :
49 8 : static struct file_system_type **find_filesystem(const char *name, unsigned len)
50 : {
51 : struct file_system_type **p;
52 32 : for (p = &file_systems; *p; p = &(*p)->next)
53 26 : if (strncmp((*p)->name, name, len) == 0 &&
54 1 : !(*p)->name[len])
55 : break;
56 8 : 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 7 : int register_filesystem(struct file_system_type * fs)
73 : {
74 7 : int res = 0;
75 : struct file_system_type ** p;
76 :
77 7 : if (fs->parameters &&
78 : !fs_validate_description(fs->name, fs->parameters))
79 : return -EINVAL;
80 :
81 7 : BUG_ON(strchr(fs->name, '.'));
82 7 : if (fs->next)
83 : return -EBUSY;
84 7 : write_lock(&file_systems_lock);
85 14 : p = find_filesystem(fs->name, strlen(fs->name));
86 7 : if (*p)
87 : res = -EBUSY;
88 : else
89 7 : *p = fs;
90 7 : write_unlock(&file_systems_lock);
91 7 : 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 0 : int unregister_filesystem(struct file_system_type * fs)
109 : {
110 : struct file_system_type ** tmp;
111 :
112 0 : write_lock(&file_systems_lock);
113 0 : tmp = &file_systems;
114 0 : while (*tmp) {
115 0 : if (fs == *tmp) {
116 0 : *tmp = fs->next;
117 0 : fs->next = NULL;
118 0 : write_unlock(&file_systems_lock);
119 0 : synchronize_rcu();
120 0 : return 0;
121 : }
122 0 : tmp = &(*tmp)->next;
123 : }
124 0 : write_unlock(&file_systems_lock);
125 :
126 0 : return -EINVAL;
127 : }
128 :
129 : EXPORT_SYMBOL(unregister_filesystem);
130 :
131 : #ifdef CONFIG_SYSFS_SYSCALL
132 0 : 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 0 : name = getname(__name);
139 0 : err = PTR_ERR(name);
140 0 : if (IS_ERR(name))
141 : return err;
142 :
143 0 : err = -EINVAL;
144 0 : read_lock(&file_systems_lock);
145 0 : for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
146 0 : if (strcmp(tmp->name, name->name) == 0) {
147 : err = index;
148 : break;
149 : }
150 : }
151 0 : read_unlock(&file_systems_lock);
152 0 : putname(name);
153 0 : return err;
154 : }
155 :
156 0 : static int fs_name(unsigned int index, char __user * buf)
157 : {
158 : struct file_system_type * tmp;
159 : int len, res;
160 :
161 0 : read_lock(&file_systems_lock);
162 0 : for (tmp = file_systems; tmp; tmp = tmp->next, index--)
163 0 : if (index <= 0 && try_module_get(tmp->owner))
164 : break;
165 0 : read_unlock(&file_systems_lock);
166 0 : if (!tmp)
167 : return -EINVAL;
168 :
169 : /* OK, we got the reference, so we can safely block */
170 0 : len = strlen(tmp->name) + 1;
171 0 : 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 0 : read_lock(&file_systems_lock);
182 0 : for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
183 : ;
184 0 : read_unlock(&file_systems_lock);
185 : return index;
186 : }
187 :
188 : /*
189 : * Whee.. Weird sysv syscall.
190 : */
191 0 : SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
192 : {
193 0 : int retval = -EINVAL;
194 :
195 0 : switch (option) {
196 : case 1:
197 0 : retval = fs_index((const char __user *) arg1);
198 0 : break;
199 :
200 : case 2:
201 0 : retval = fs_name(arg1, (char __user *) arg2);
202 0 : break;
203 :
204 : case 3:
205 0 : retval = fs_maxindex();
206 0 : break;
207 : }
208 0 : return retval;
209 : }
210 : #endif
211 :
212 0 : int __init list_bdev_fs_names(char *buf, size_t size)
213 : {
214 : struct file_system_type *p;
215 : size_t len;
216 0 : int count = 0;
217 :
218 0 : read_lock(&file_systems_lock);
219 0 : for (p = file_systems; p; p = p->next) {
220 0 : if (!(p->fs_flags & FS_REQUIRES_DEV))
221 0 : continue;
222 0 : len = strlen(p->name) + 1;
223 0 : if (len > size) {
224 0 : pr_warn("%s: truncating file system list\n", __func__);
225 0 : break;
226 : }
227 0 : memcpy(buf, p->name, len);
228 0 : buf += len;
229 0 : size -= len;
230 0 : count++;
231 : }
232 0 : read_unlock(&file_systems_lock);
233 0 : return count;
234 : }
235 :
236 : #ifdef CONFIG_PROC_FS
237 0 : static int filesystems_proc_show(struct seq_file *m, void *v)
238 : {
239 : struct file_system_type * tmp;
240 :
241 0 : read_lock(&file_systems_lock);
242 0 : tmp = file_systems;
243 0 : while (tmp) {
244 0 : seq_printf(m, "%s\t%s\n",
245 0 : (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
246 : tmp->name);
247 0 : tmp = tmp->next;
248 : }
249 0 : read_unlock(&file_systems_lock);
250 0 : return 0;
251 : }
252 :
253 1 : static int __init proc_filesystems_init(void)
254 : {
255 1 : proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
256 1 : 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 1 : read_lock(&file_systems_lock);
266 1 : fs = *(find_filesystem(name, len));
267 : if (fs && !try_module_get(fs->owner))
268 : fs = NULL;
269 1 : read_unlock(&file_systems_lock);
270 : return fs;
271 : }
272 :
273 1 : struct file_system_type *get_fs_type(const char *name)
274 : {
275 : struct file_system_type *fs;
276 1 : const char *dot = strchr(name, '.');
277 2 : int len = dot ? dot - name : strlen(name);
278 :
279 1 : 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 1 : if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
288 0 : put_filesystem(fs);
289 0 : fs = NULL;
290 : }
291 1 : return fs;
292 : }
293 :
294 : EXPORT_SYMBOL(get_fs_type);
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