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 &&
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 
unregister_filesystem(struct file_system_type * fs)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
fs_index(const char __user * __name)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 
fs_name(unsigned int index,char __user * buf)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 
fs_maxindex(void)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  */
SYSCALL_DEFINE3(sysfs,int,option,unsigned long,arg1,unsigned long,arg2)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 
list_bdev_fs_names(char * buf,size_t size)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
filesystems_proc_show(struct seq_file * m,void * v)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 
proc_filesystems_init(void)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 
__get_fs_type(const char * name,int len)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 
get_fs_type(const char * name)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