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Greg Kroah-Hartmanb2441312017-11-01 15:07:57 +01001// SPDX-License-Identifier: GPL-2.0
Linus Torvalds1da177e2005-04-16 15:20:36 -07002/*
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>
Alexey Dobriyan68274002008-10-04 14:08:37 +040012#include <linux/proc_fs.h>
13#include <linux/seq_file.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070014#include <linux/kmod.h>
15#include <linux/init.h>
16#include <linux/module.h>
Tejun Heo5a0e3ad2010-03-24 17:04:11 +090017#include <linux/slab.h>
Linus Torvalds7c0f6ba2016-12-24 11:46:01 -080018#include <linux/uaccess.h>
David Howells3e1aeb02018-11-01 23:07:25 +000019#include <linux/fs_parser.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070020
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
34static struct file_system_type *file_systems;
35static DEFINE_RWLOCK(file_systems_lock);
36
37/* WARNING: This can be used only if we _already_ own a reference */
David Howellsee416bc2017-07-04 17:25:16 +010038struct file_system_type *get_filesystem(struct file_system_type *fs)
Linus Torvalds1da177e2005-04-16 15:20:36 -070039{
40 __module_get(fs->owner);
David Howellsee416bc2017-07-04 17:25:16 +010041 return fs;
Linus Torvalds1da177e2005-04-16 15:20:36 -070042}
43
44void put_filesystem(struct file_system_type *fs)
45{
46 module_put(fs->owner);
47}
48
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -070049static struct file_system_type **find_filesystem(const char *name, unsigned len)
Linus Torvalds1da177e2005-04-16 15:20:36 -070050{
51 struct file_system_type **p;
Al Viro558041d2016-01-19 11:40:44 -050052 for (p = &file_systems; *p; p = &(*p)->next)
53 if (strncmp((*p)->name, name, len) == 0 &&
54 !(*p)->name[len])
Linus Torvalds1da177e2005-04-16 15:20:36 -070055 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
72int register_filesystem(struct file_system_type * fs)
73{
74 int res = 0;
75 struct file_system_type ** p;
76
Eric Sandeen96cafb92019-12-06 10:45:01 -060077 if (fs->parameters &&
78 !fs_validate_description(fs->name, fs->parameters))
David Howells3e1aeb02018-11-01 23:07:25 +000079 return -EINVAL;
80
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -070081 BUG_ON(strchr(fs->name, '.'));
Linus Torvalds1da177e2005-04-16 15:20:36 -070082 if (fs->next)
83 return -EBUSY;
Linus Torvalds1da177e2005-04-16 15:20:36 -070084 write_lock(&file_systems_lock);
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -070085 p = find_filesystem(fs->name, strlen(fs->name));
Linus Torvalds1da177e2005-04-16 15:20:36 -070086 if (*p)
87 res = -EBUSY;
88 else
89 *p = fs;
90 write_unlock(&file_systems_lock);
91 return res;
92}
93
94EXPORT_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
108int 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);
Milton Millerfff3e5a2011-04-14 10:30:08 -0500119 synchronize_rcu();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700120 return 0;
121 }
122 tmp = &(*tmp)->next;
123 }
124 write_unlock(&file_systems_lock);
Nick Piggin31e6b012011-01-07 17:49:52 +1100125
Linus Torvalds1da177e2005-04-16 15:20:36 -0700126 return -EINVAL;
127}
128
129EXPORT_SYMBOL(unregister_filesystem);
130
Fabian Frederick6af9f7b2014-04-03 14:48:25 -0700131#ifdef CONFIG_SYSFS_SYSCALL
Linus Torvalds1da177e2005-04-16 15:20:36 -0700132static int fs_index(const char __user * __name)
133{
134 struct file_system_type * tmp;
Jeff Layton91a27b22012-10-10 15:25:28 -0400135 struct filename *name;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700136 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++) {
Jeff Layton91a27b22012-10-10 15:25:28 -0400146 if (strcmp(tmp->name, name->name) == 0) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700147 err = index;
148 break;
149 }
150 }
151 read_unlock(&file_systems_lock);
152 putname(name);
153 return err;
154}
155
156static 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
176static 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 */
Heiko Carstens1e7bfb22009-01-14 14:14:29 +0100191SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700192{
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}
Fabian Frederick6af9f7b2014-04-03 14:48:25 -0700210#endif
Linus Torvalds1da177e2005-04-16 15:20:36 -0700211
Tetsuo Handa38e23c92009-04-09 20:17:52 +0900212int __init get_filesystem_list(char *buf)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700213{
214 int len = 0;
215 struct file_system_type * tmp;
216
217 read_lock(&file_systems_lock);
218 tmp = file_systems;
219 while (tmp && len < PAGE_SIZE - 80) {
220 len += sprintf(buf+len, "%s\t%s\n",
221 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
222 tmp->name);
223 tmp = tmp->next;
224 }
225 read_unlock(&file_systems_lock);
226 return len;
227}
228
Alexey Dobriyan68274002008-10-04 14:08:37 +0400229#ifdef CONFIG_PROC_FS
230static int filesystems_proc_show(struct seq_file *m, void *v)
231{
232 struct file_system_type * tmp;
233
234 read_lock(&file_systems_lock);
235 tmp = file_systems;
236 while (tmp) {
237 seq_printf(m, "%s\t%s\n",
238 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
239 tmp->name);
240 tmp = tmp->next;
241 }
242 read_unlock(&file_systems_lock);
243 return 0;
244}
245
Alexey Dobriyan68274002008-10-04 14:08:37 +0400246static int __init proc_filesystems_init(void)
247{
Christoph Hellwig3f3942a2018-05-15 15:57:23 +0200248 proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
Alexey Dobriyan68274002008-10-04 14:08:37 +0400249 return 0;
250}
251module_init(proc_filesystems_init);
252#endif
253
Li Zefand8e9650d2008-12-25 13:32:15 +0800254static struct file_system_type *__get_fs_type(const char *name, int len)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700255{
256 struct file_system_type *fs;
257
258 read_lock(&file_systems_lock);
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -0700259 fs = *(find_filesystem(name, len));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700260 if (fs && !try_module_get(fs->owner))
261 fs = NULL;
262 read_unlock(&file_systems_lock);
Li Zefand8e9650d2008-12-25 13:32:15 +0800263 return fs;
264}
265
266struct file_system_type *get_fs_type(const char *name)
267{
268 struct file_system_type *fs;
269 const char *dot = strchr(name, '.');
270 int len = dot ? dot - name : strlen(name);
271
272 fs = __get_fs_type(name, len);
Luis R. Rodriguez41124db2017-06-01 11:08:01 -0700273 if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
Li Zefand8e9650d2008-12-25 13:32:15 +0800274 fs = __get_fs_type(name, len);
Eric Biggers26c5d782020-04-10 14:33:47 -0700275 if (!fs)
276 pr_warn_once("request_module fs-%.*s succeeded, but still no fs?\n",
277 len, name);
Luis R. Rodriguez41124db2017-06-01 11:08:01 -0700278 }
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -0700279
280 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
281 put_filesystem(fs);
282 fs = NULL;
283 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700284 return fs;
285}
286
287EXPORT_SYMBOL(get_fs_type);