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