[mirror_ubuntu-eoan-kernel.git] / fs / filesystems.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/filesystems.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  table of configured filesystems
 */

#include <linux/syscalls.h>
#include <linux/fs.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/kmod.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/uaccess.h>

/*
 * Handling of filesystem drivers list.
 * Rules:
 *	Inclusion to/removals from/scanning of list are protected by spinlock.
 *	During the unload module must call unregister_filesystem().
 *	We can access the fields of list element if:
 *		1) spinlock is held or
 *		2) we hold the reference to the module.
 *	The latter can be guaranteed by call of try_module_get(); if it
 *	returned 0 we must skip the element, otherwise we got the reference.
 *	Once the reference is obtained we can drop the spinlock.
 */

static struct file_system_type *file_systems;
static DEFINE_RWLOCK(file_systems_lock);

/* WARNING: This can be used only if we _already_ own a reference */
struct file_system_type *get_filesystem(struct file_system_type *fs)
{
	__module_get(fs->owner);
	return fs;
}

void put_filesystem(struct file_system_type *fs)
{
	module_put(fs->owner);
}

static struct file_system_type **find_filesystem(const char *name, unsigned len)
{
	struct file_system_type **p;
	for (p = &file_systems; *p; p = &(*p)->next)
		if (strncmp((*p)->name, name, len) == 0 &&
		    !(*p)->name[len])
			break;
	return p;
}

/**
 *	register_filesystem - register a new filesystem
 *	@fs: the file system structure
 *
 *	Adds the file system passed to the list of file systems the kernel
 *	is aware of for mount and other syscalls. Returns 0 on success,
 *	or a negative errno code on an error.
 *
 *	The &struct file_system_type that is passed is linked into the kernel 
 *	structures and must not be freed until the file system has been
 *	unregistered.
 */
 
int register_filesystem(struct file_system_type * fs)
{
	int res = 0;
	struct file_system_type ** p;

	BUG_ON(strchr(fs->name, '.'));
	if (fs->next)
		return -EBUSY;
	write_lock(&file_systems_lock);
	p = find_filesystem(fs->name, strlen(fs->name));
	if (*p)
		res = -EBUSY;
	else
		*p = fs;
	write_unlock(&file_systems_lock);
	return res;
}

EXPORT_SYMBOL(register_filesystem);

/**
 *	unregister_filesystem - unregister a file system
 *	@fs: filesystem to unregister
 *
 *	Remove a file system that was previously successfully registered
 *	with the kernel. An error is returned if the file system is not found.
 *	Zero is returned on a success.
 *	
 *	Once this function has returned the &struct file_system_type structure
 *	may be freed or reused.
 */
 
int unregister_filesystem(struct file_system_type * fs)
{
	struct file_system_type ** tmp;

	write_lock(&file_systems_lock);
	tmp = &file_systems;
	while (*tmp) {
		if (fs == *tmp) {
			*tmp = fs->next;
			fs->next = NULL;
			write_unlock(&file_systems_lock);
			synchronize_rcu();
			return 0;
		}
		tmp = &(*tmp)->next;
	}
	write_unlock(&file_systems_lock);

	return -EINVAL;
}

EXPORT_SYMBOL(unregister_filesystem);

#ifdef CONFIG_SYSFS_SYSCALL
static int fs_index(const char __user * __name)
{
	struct file_system_type * tmp;
	struct filename *name;
	int err, index;

	name = getname(__name);
	err = PTR_ERR(name);
	if (IS_ERR(name))
		return err;

	err = -EINVAL;
	read_lock(&file_systems_lock);
	for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
		if (strcmp(tmp->name, name->name) == 0) {
			err = index;
			break;
		}
	}
	read_unlock(&file_systems_lock);
	putname(name);
	return err;
}

static int fs_name(unsigned int index, char __user * buf)
{
	struct file_system_type * tmp;
	int len, res;

	read_lock(&file_systems_lock);
	for (tmp = file_systems; tmp; tmp = tmp->next, index--)
		if (index <= 0 && try_module_get(tmp->owner))
			break;
	read_unlock(&file_systems_lock);
	if (!tmp)
		return -EINVAL;

	/* OK, we got the reference, so we can safely block */
	len = strlen(tmp->name) + 1;
	res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
	put_filesystem(tmp);
	return res;
}

static int fs_maxindex(void)
{
	struct file_system_type * tmp;
	int index;

	read_lock(&file_systems_lock);
	for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
		;
	read_unlock(&file_systems_lock);
	return index;
}

/*
 * Whee.. Weird sysv syscall. 
 */
SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
{
	int retval = -EINVAL;

	switch (option) {
		case 1:
			retval = fs_index((const char __user *) arg1);
			break;

		case 2:
			retval = fs_name(arg1, (char __user *) arg2);
			break;

		case 3:
			retval = fs_maxindex();
			break;
	}
	return retval;
}
#endif

int __init get_filesystem_list(char *buf)
{
	int len = 0;
	struct file_system_type * tmp;

	read_lock(&file_systems_lock);
	tmp = file_systems;
	while (tmp && len < PAGE_SIZE - 80) {
		len += sprintf(buf+len, "%s\t%s\n",
			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
			tmp->name);
		tmp = tmp->next;
	}
	read_unlock(&file_systems_lock);
	return len;
}

#ifdef CONFIG_PROC_FS
static int filesystems_proc_show(struct seq_file *m, void *v)
{
	struct file_system_type * tmp;

	read_lock(&file_systems_lock);
	tmp = file_systems;
	while (tmp) {
		seq_printf(m, "%s\t%s\n",
			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
			tmp->name);
		tmp = tmp->next;
	}
	read_unlock(&file_systems_lock);
	return 0;
}

static int __init proc_filesystems_init(void)
{
	proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
	return 0;
}
module_init(proc_filesystems_init);
#endif

static struct file_system_type *__get_fs_type(const char *name, int len)
{
	struct file_system_type *fs;

	read_lock(&file_systems_lock);
	fs = *(find_filesystem(name, len));
	if (fs && !try_module_get(fs->owner))
		fs = NULL;
	read_unlock(&file_systems_lock);
	return fs;
}

struct file_system_type *get_fs_type(const char *name)
{
	struct file_system_type *fs;
	const char *dot = strchr(name, '.');
	int len = dot ? dot - name : strlen(name);

	fs = __get_fs_type(name, len);
	if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
		fs = __get_fs_type(name, len);
		WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
	}

	if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
		put_filesystem(fs);
		fs = NULL;
	}
	return fs;
}

EXPORT_SYMBOL(get_fs_type);
Commit	Line	Data
b2441318	1	// SPDX-License-Identifier: GPL-2.0
1da177e4 LT	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>
68274007 AD	12	#include <linux/proc_fs.h>
68274007 AD	13	#include <linux/seq_file.h>
1da177e4 LT	14	#include <linux/kmod.h>
	15	#include <linux/init.h>
	16	#include <linux/module.h>
5a0e3ad6	17	#include <linux/slab.h>
7c0f6ba6	18	#include <linux/uaccess.h>
1da177e4 LT	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 */
ee416bcd	37	struct file_system_type get_filesystem(struct file_system_type fs)
1da177e4 LT	38	{
1da177e4 LT	39	__module_get(fs->owner);
ee416bcd	40	return fs;
1da177e4 LT	41	}
	42
	43	void put_filesystem(struct file_system_type *fs)
	44	{
	45	module_put(fs->owner);
	46	}
	47
79c0b2df	48	static struct file_system_type *find_filesystem(const char name, unsigned len)
1da177e4 LT	49	{
1da177e4 LT	50	struct file_system_type **p;
558041d8 AV	51	for (p = &file_systems; p; p = &(p)->next)
	52	if (strncmp((*p)->name, name, len) == 0 &&
	53	!(*p)->name[len])
1da177e4 LT	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
	71	int register_filesystem(struct file_system_type * fs)
	72	{
	73	int res = 0;
	74	struct file_system_type ** p;
	75
79c0b2df	76	BUG_ON(strchr(fs->name, '.'));
1da177e4 LT	77	if (fs->next)
1da177e4 LT	78	return -EBUSY;
1da177e4	79	write_lock(&file_systems_lock);
79c0b2df	80	p = find_filesystem(fs->name, strlen(fs->name));
1da177e4 LT	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
	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);
fff3e5ad	114	synchronize_rcu();
1da177e4 LT	115	return 0;
	116	}
	117	tmp = &(*tmp)->next;
	118	}
	119	write_unlock(&file_systems_lock);
31e6b01f	120
1da177e4 LT	121	return -EINVAL;
	122	}
	123
	124	EXPORT_SYMBOL(unregister_filesystem);
	125
6af9f7bf	126	#ifdef CONFIG_SYSFS_SYSCALL
1da177e4 LT	127	static int fs_index(const char __user * __name)
	128	{
	129	struct file_system_type * tmp;
91a27b2a	130	struct filename *name;
1da177e4 LT	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++) {
91a27b2a	141	if (strcmp(tmp->name, name->name) == 0) {
1da177e4 LT	142	err = index;
	143	break;
	144	}
	145	}
	146	read_unlock(&file_systems_lock);
	147	putname(name);
	148	return err;
	149	}
	150
	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
	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	*/
1e7bfb21	186	SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
1da177e4 LT	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	}
6af9f7bf	205	#endif
1da177e4	206
38e23c95	207	int __init get_filesystem_list(char *buf)
1da177e4 LT	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
68274007 AD	224	#ifdef CONFIG_PROC_FS
	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
68274007 AD	241	static int __init proc_filesystems_init(void)
68274007 AD	242	{
3f3942ac	243	proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
68274007 AD	244	return 0;
	245	}
	246	module_init(proc_filesystems_init);
	247	#endif
	248
d8e9650d	249	static struct file_system_type __get_fs_type(const char name, int len)
1da177e4 LT	250	{
	251	struct file_system_type *fs;
	252
	253	read_lock(&file_systems_lock);
79c0b2df	254	fs = *(find_filesystem(name, len));
1da177e4 LT	255	if (fs && !try_module_get(fs->owner))
	256	fs = NULL;
	257	read_unlock(&file_systems_lock);
d8e9650d LZ	258	return fs;
	259	}
	260
	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);
41124db8	268	if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
d8e9650d	269	fs = __get_fs_type(name, len);
41124db8 LR	270	WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
41124db8 LR	271	}
79c0b2df MS	272
	273	if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
	274	put_filesystem(fs);
	275	fs = NULL;
	276	}
1da177e4 LT	277	return fs;
	278	}
	279
	280	EXPORT_SYMBOL(get_fs_type);