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 */
get_filesystem(struct file_system_type * fs)38 struct file_system_type *get_filesystem(struct file_system_type *fs)
39 {
40 __module_get(fs->owner);
41 return fs;
42 }
43
put_filesystem(struct file_system_type * fs)44 void put_filesystem(struct file_system_type *fs)
45 {
46 module_put(fs->owner);
47 }
48
find_filesystem(const char * name,unsigned len)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
register_filesystem(struct file_system_type * fs)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 && !fs_validate_description(fs->parameters))
78 return -EINVAL;
79
80 BUG_ON(strchr(fs->name, '.'));
81 if (fs->next)
82 return -EBUSY;
83 write_lock(&file_systems_lock);
84 p = find_filesystem(fs->name, strlen(fs->name));
85 if (*p)
86 res = -EBUSY;
87 else
88 *p = fs;
89 write_unlock(&file_systems_lock);
90 return res;
91 }
92
93 EXPORT_SYMBOL(register_filesystem);
94
95 /**
96 * unregister_filesystem - unregister a file system
97 * @fs: filesystem to unregister
98 *
99 * Remove a file system that was previously successfully registered
100 * with the kernel. An error is returned if the file system is not found.
101 * Zero is returned on a success.
102 *
103 * Once this function has returned the &struct file_system_type structure
104 * may be freed or reused.
105 */
106
unregister_filesystem(struct file_system_type * fs)107 int unregister_filesystem(struct file_system_type * fs)
108 {
109 struct file_system_type ** tmp;
110
111 write_lock(&file_systems_lock);
112 tmp = &file_systems;
113 while (*tmp) {
114 if (fs == *tmp) {
115 *tmp = fs->next;
116 fs->next = NULL;
117 write_unlock(&file_systems_lock);
118 synchronize_rcu();
119 return 0;
120 }
121 tmp = &(*tmp)->next;
122 }
123 write_unlock(&file_systems_lock);
124
125 return -EINVAL;
126 }
127
128 EXPORT_SYMBOL(unregister_filesystem);
129
130 #ifdef CONFIG_SYSFS_SYSCALL
fs_index(const char __user * __name)131 static int fs_index(const char __user * __name)
132 {
133 struct file_system_type * tmp;
134 struct filename *name;
135 int err, index;
136
137 name = getname(__name);
138 err = PTR_ERR(name);
139 if (IS_ERR(name))
140 return err;
141
142 err = -EINVAL;
143 read_lock(&file_systems_lock);
144 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
145 if (strcmp(tmp->name, name->name) == 0) {
146 err = index;
147 break;
148 }
149 }
150 read_unlock(&file_systems_lock);
151 putname(name);
152 return err;
153 }
154
fs_name(unsigned int index,char __user * buf)155 static int fs_name(unsigned int index, char __user * buf)
156 {
157 struct file_system_type * tmp;
158 int len, res;
159
160 read_lock(&file_systems_lock);
161 for (tmp = file_systems; tmp; tmp = tmp->next, index--)
162 if (index <= 0 && try_module_get(tmp->owner))
163 break;
164 read_unlock(&file_systems_lock);
165 if (!tmp)
166 return -EINVAL;
167
168 /* OK, we got the reference, so we can safely block */
169 len = strlen(tmp->name) + 1;
170 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
171 put_filesystem(tmp);
172 return res;
173 }
174
fs_maxindex(void)175 static int fs_maxindex(void)
176 {
177 struct file_system_type * tmp;
178 int index;
179
180 read_lock(&file_systems_lock);
181 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
182 ;
183 read_unlock(&file_systems_lock);
184 return index;
185 }
186
187 /*
188 * Whee.. Weird sysv syscall.
189 */
SYSCALL_DEFINE3(sysfs,int,option,unsigned long,arg1,unsigned long,arg2)190 SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
191 {
192 int retval = -EINVAL;
193
194 switch (option) {
195 case 1:
196 retval = fs_index((const char __user *) arg1);
197 break;
198
199 case 2:
200 retval = fs_name(arg1, (char __user *) arg2);
201 break;
202
203 case 3:
204 retval = fs_maxindex();
205 break;
206 }
207 return retval;
208 }
209 #endif
210
get_filesystem_list(char * buf)211 int __init get_filesystem_list(char *buf)
212 {
213 int len = 0;
214 struct file_system_type * tmp;
215
216 read_lock(&file_systems_lock);
217 tmp = file_systems;
218 while (tmp && len < PAGE_SIZE - 80) {
219 len += sprintf(buf+len, "%s\t%s\n",
220 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
221 tmp->name);
222 tmp = tmp->next;
223 }
224 read_unlock(&file_systems_lock);
225 return len;
226 }
227
228 #ifdef CONFIG_PROC_FS
filesystems_proc_show(struct seq_file * m,void * v)229 static int filesystems_proc_show(struct seq_file *m, void *v)
230 {
231 struct file_system_type * tmp;
232
233 read_lock(&file_systems_lock);
234 tmp = file_systems;
235 while (tmp) {
236 seq_printf(m, "%s\t%s\n",
237 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
238 tmp->name);
239 tmp = tmp->next;
240 }
241 read_unlock(&file_systems_lock);
242 return 0;
243 }
244
proc_filesystems_init(void)245 static int __init proc_filesystems_init(void)
246 {
247 proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
248 return 0;
249 }
250 module_init(proc_filesystems_init);
251 #endif
252
__get_fs_type(const char * name,int len)253 static struct file_system_type *__get_fs_type(const char *name, int len)
254 {
255 struct file_system_type *fs;
256
257 read_lock(&file_systems_lock);
258 fs = *(find_filesystem(name, len));
259 if (fs && !try_module_get(fs->owner))
260 fs = NULL;
261 read_unlock(&file_systems_lock);
262 return fs;
263 }
264
get_fs_type(const char * name)265 struct file_system_type *get_fs_type(const char *name)
266 {
267 struct file_system_type *fs;
268 const char *dot = strchr(name, '.');
269 int len = dot ? dot - name : strlen(name);
270
271 fs = __get_fs_type(name, len);
272 if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
273 fs = __get_fs_type(name, len);
274 WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
275 }
276
277 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
278 put_filesystem(fs);
279 fs = NULL;
280 }
281 return fs;
282 }
283
284 EXPORT_SYMBOL(get_fs_type);
285
