[linux.git] / fs / fsopen.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* Filesystem access-by-fd.
 *
 * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 */

#include <linux/fs_context.h>
#include <linux/fs_parser.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/syscalls.h>
#include <linux/security.h>
#include <linux/anon_inodes.h>
#include <linux/namei.h>
#include <linux/file.h>
#include <uapi/linux/mount.h>
#include "internal.h"
#include "mount.h"

/*
 * Allow the user to read back any error, warning or informational messages.
 */
static ssize_t fscontext_read(struct file *file,
			      char __user *_buf, size_t len, loff_t *pos)
{
	struct fs_context *fc = file->private_data;
	struct fc_log *log = fc->log;
	unsigned int logsize = ARRAY_SIZE(log->buffer);
	ssize_t ret;
	char *p;
	bool need_free;
	int index, n;

	ret = mutex_lock_interruptible(&fc->uapi_mutex);
	if (ret < 0)
		return ret;

	if (log->head == log->tail) {
		mutex_unlock(&fc->uapi_mutex);
		return -ENODATA;
	}

	index = log->tail & (logsize - 1);
	p = log->buffer[index];
	need_free = log->need_free & (1 << index);
	log->buffer[index] = NULL;
	log->need_free &= ~(1 << index);
	log->tail++;
	mutex_unlock(&fc->uapi_mutex);

	ret = -EMSGSIZE;
	n = strlen(p);
	if (n > len)
		goto err_free;
	ret = -EFAULT;
	if (copy_to_user(_buf, p, n) != 0)
		goto err_free;
	ret = n;

err_free:
	if (need_free)
		kfree(p);
	return ret;
}

static int fscontext_release(struct inode *inode, struct file *file)
{
	struct fs_context *fc = file->private_data;

	if (fc) {
		file->private_data = NULL;
		put_fs_context(fc);
	}
	return 0;
}

const struct file_operations fscontext_fops = {
	.read		= fscontext_read,
	.release	= fscontext_release,
	.llseek		= no_llseek,
};

/*
 * Attach a filesystem context to a file and an fd.
 */
static int fscontext_create_fd(struct fs_context *fc, unsigned int o_flags)
{
	int fd;

	fd = anon_inode_getfd("[fscontext]", &fscontext_fops, fc,
			      O_RDWR | o_flags);
	if (fd < 0)
		put_fs_context(fc);
	return fd;
}

static int fscontext_alloc_log(struct fs_context *fc)
{
	fc->log = kzalloc(sizeof(*fc->log), GFP_KERNEL);
	if (!fc->log)
		return -ENOMEM;
	refcount_set(&fc->log->usage, 1);
	fc->log->owner = fc->fs_type->owner;
	return 0;
}

/*
 * Open a filesystem by name so that it can be configured for mounting.
 *
 * We are allowed to specify a container in which the filesystem will be
 * opened, thereby indicating which namespaces will be used (notably, which
 * network namespace will be used for network filesystems).
 */
SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags)
{
	struct file_system_type *fs_type;
	struct fs_context *fc;
	const char *fs_name;
	int ret;

	if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
		return -EPERM;

	if (flags & ~FSOPEN_CLOEXEC)
		return -EINVAL;

	fs_name = strndup_user(_fs_name, PAGE_SIZE);
	if (IS_ERR(fs_name))
		return PTR_ERR(fs_name);

	fs_type = get_fs_type(fs_name);
	kfree(fs_name);
	if (!fs_type)
		return -ENODEV;

	fc = fs_context_for_mount(fs_type, 0);
	put_filesystem(fs_type);
	if (IS_ERR(fc))
		return PTR_ERR(fc);

	fc->phase = FS_CONTEXT_CREATE_PARAMS;

	ret = fscontext_alloc_log(fc);
	if (ret < 0)
		goto err_fc;

	return fscontext_create_fd(fc, flags & FSOPEN_CLOEXEC ? O_CLOEXEC : 0);

err_fc:
	put_fs_context(fc);
	return ret;
}

/*
 * Pick a superblock into a context for reconfiguration.
 */
SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags)
{
	struct fs_context *fc;
	struct path target;
	unsigned int lookup_flags;
	int ret;

	if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
		return -EPERM;

	if ((flags & ~(FSPICK_CLOEXEC |
		       FSPICK_SYMLINK_NOFOLLOW |
		       FSPICK_NO_AUTOMOUNT |
		       FSPICK_EMPTY_PATH)) != 0)
		return -EINVAL;

	lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
	if (flags & FSPICK_SYMLINK_NOFOLLOW)
		lookup_flags &= ~LOOKUP_FOLLOW;
	if (flags & FSPICK_NO_AUTOMOUNT)
		lookup_flags &= ~LOOKUP_AUTOMOUNT;
	if (flags & FSPICK_EMPTY_PATH)
		lookup_flags |= LOOKUP_EMPTY;
	ret = user_path_at(dfd, path, lookup_flags, &target);
	if (ret < 0)
		goto err;

	ret = -EINVAL;
	if (target.mnt->mnt_root != target.dentry)
		goto err_path;

	fc = fs_context_for_reconfigure(target.dentry, 0, 0);
	if (IS_ERR(fc)) {
		ret = PTR_ERR(fc);
		goto err_path;
	}

	fc->phase = FS_CONTEXT_RECONF_PARAMS;

	ret = fscontext_alloc_log(fc);
	if (ret < 0)
		goto err_fc;

	path_put(&target);
	return fscontext_create_fd(fc, flags & FSPICK_CLOEXEC ? O_CLOEXEC : 0);

err_fc:
	put_fs_context(fc);
err_path:
	path_put(&target);
err:
	return ret;
}

/*
 * Check the state and apply the configuration.  Note that this function is
 * allowed to 'steal' the value by setting param->xxx to NULL before returning.
 */
static int vfs_fsconfig_locked(struct fs_context *fc, int cmd,
			       struct fs_parameter *param)
{
	struct super_block *sb;
	int ret;

	ret = finish_clean_context(fc);
	if (ret)
		return ret;
	switch (cmd) {
	case FSCONFIG_CMD_CREATE:
		if (fc->phase != FS_CONTEXT_CREATE_PARAMS)
			return -EBUSY;
		fc->phase = FS_CONTEXT_CREATING;
		ret = vfs_get_tree(fc);
		if (ret)
			break;
		sb = fc->root->d_sb;
		ret = security_sb_kern_mount(sb);
		if (unlikely(ret)) {
			fc_drop_locked(fc);
			break;
		}
		up_write(&sb->s_umount);
		fc->phase = FS_CONTEXT_AWAITING_MOUNT;
		return 0;
	case FSCONFIG_CMD_RECONFIGURE:
		if (fc->phase != FS_CONTEXT_RECONF_PARAMS)
			return -EBUSY;
		fc->phase = FS_CONTEXT_RECONFIGURING;
		sb = fc->root->d_sb;
		if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
			ret = -EPERM;
			break;
		}
		down_write(&sb->s_umount);
		ret = reconfigure_super(fc);
		up_write(&sb->s_umount);
		if (ret)
			break;
		vfs_clean_context(fc);
		return 0;
	default:
		if (fc->phase != FS_CONTEXT_CREATE_PARAMS &&
		    fc->phase != FS_CONTEXT_RECONF_PARAMS)
			return -EBUSY;

		return vfs_parse_fs_param(fc, param);
	}
	fc->phase = FS_CONTEXT_FAILED;
	return ret;
}

/**
 * sys_fsconfig - Set parameters and trigger actions on a context
 * @fd: The filesystem context to act upon
 * @cmd: The action to take
 * @_key: Where appropriate, the parameter key to set
 * @_value: Where appropriate, the parameter value to set
 * @aux: Additional information for the value
 *
 * This system call is used to set parameters on a context, including
 * superblock settings, data source and security labelling.
 *
 * Actions include triggering the creation of a superblock and the
 * reconfiguration of the superblock attached to the specified context.
 *
 * When setting a parameter, @cmd indicates the type of value being proposed
 * and @_key indicates the parameter to be altered.
 *
 * @_value and @aux are used to specify the value, should a value be required:
 *
 * (*) fsconfig_set_flag: No value is specified.  The parameter must be boolean
 *     in nature.  The key may be prefixed with "no" to invert the
 *     setting. @_value must be NULL and @aux must be 0.
 *
 * (*) fsconfig_set_string: A string value is specified.  The parameter can be
 *     expecting boolean, integer, string or take a path.  A conversion to an
 *     appropriate type will be attempted (which may include looking up as a
 *     path).  @_value points to a NUL-terminated string and @aux must be 0.
 *
 * (*) fsconfig_set_binary: A binary blob is specified.  @_value points to the
 *     blob and @aux indicates its size.  The parameter must be expecting a
 *     blob.
 *
 * (*) fsconfig_set_path: A non-empty path is specified.  The parameter must be
 *     expecting a path object.  @_value points to a NUL-terminated string that
 *     is the path and @aux is a file descriptor at which to start a relative
 *     lookup or AT_FDCWD.
 *
 * (*) fsconfig_set_path_empty: As fsconfig_set_path, but with AT_EMPTY_PATH
 *     implied.
 *
 * (*) fsconfig_set_fd: An open file descriptor is specified.  @_value must be
 *     NULL and @aux indicates the file descriptor.
 */
SYSCALL_DEFINE5(fsconfig,
		int, fd,
		unsigned int, cmd,
		const char __user *, _key,
		const void __user *, _value,
		int, aux)
{
	struct fs_context *fc;
	struct fd f;
	int ret;

	struct fs_parameter param = {
		.type	= fs_value_is_undefined,
	};

	if (fd < 0)
		return -EINVAL;

	switch (cmd) {
	case FSCONFIG_SET_FLAG:
		if (!_key || _value || aux)
			return -EINVAL;
		break;
	case FSCONFIG_SET_STRING:
		if (!_key || !_value || aux)
			return -EINVAL;
		break;
	case FSCONFIG_SET_BINARY:
		if (!_key || !_value || aux <= 0 || aux > 1024 * 1024)
			return -EINVAL;
		break;
	case FSCONFIG_SET_PATH:
	case FSCONFIG_SET_PATH_EMPTY:
		if (!_key || !_value || (aux != AT_FDCWD && aux < 0))
			return -EINVAL;
		break;
	case FSCONFIG_SET_FD:
		if (!_key || _value || aux < 0)
			return -EINVAL;
		break;
	case FSCONFIG_CMD_CREATE:
	case FSCONFIG_CMD_RECONFIGURE:
		if (_key || _value || aux)
			return -EINVAL;
		break;
	default:
		return -EOPNOTSUPP;
	}

	f = fdget(fd);
	if (!f.file)
		return -EBADF;
	ret = -EINVAL;
	if (f.file->f_op != &fscontext_fops)
		goto out_f;

	fc = f.file->private_data;
	if (fc->ops == &legacy_fs_context_ops) {
		switch (cmd) {
		case FSCONFIG_SET_BINARY:
		case FSCONFIG_SET_PATH:
		case FSCONFIG_SET_PATH_EMPTY:
		case FSCONFIG_SET_FD:
			ret = -EOPNOTSUPP;
			goto out_f;
		}
	}

	if (_key) {
		param.key = strndup_user(_key, 256);
		if (IS_ERR(param.key)) {
			ret = PTR_ERR(param.key);
			goto out_f;
		}
	}

	switch (cmd) {
	case FSCONFIG_SET_FLAG:
		param.type = fs_value_is_flag;
		break;
	case FSCONFIG_SET_STRING:
		param.type = fs_value_is_string;
		param.string = strndup_user(_value, 256);
		if (IS_ERR(param.string)) {
			ret = PTR_ERR(param.string);
			goto out_key;
		}
		param.size = strlen(param.string);
		break;
	case FSCONFIG_SET_BINARY:
		param.type = fs_value_is_blob;
		param.size = aux;
		param.blob = memdup_user_nul(_value, aux);
		if (IS_ERR(param.blob)) {
			ret = PTR_ERR(param.blob);
			goto out_key;
		}
		break;
	case FSCONFIG_SET_PATH:
		param.type = fs_value_is_filename;
		param.name = getname_flags(_value, 0, NULL);
		if (IS_ERR(param.name)) {
			ret = PTR_ERR(param.name);
			goto out_key;
		}
		param.dirfd = aux;
		param.size = strlen(param.name->name);
		break;
	case FSCONFIG_SET_PATH_EMPTY:
		param.type = fs_value_is_filename_empty;
		param.name = getname_flags(_value, LOOKUP_EMPTY, NULL);
		if (IS_ERR(param.name)) {
			ret = PTR_ERR(param.name);
			goto out_key;
		}
		param.dirfd = aux;
		param.size = strlen(param.name->name);
		break;
	case FSCONFIG_SET_FD:
		param.type = fs_value_is_file;
		ret = -EBADF;
		param.file = fget(aux);
		if (!param.file)
			goto out_key;
		break;
	default:
		break;
	}

	ret = mutex_lock_interruptible(&fc->uapi_mutex);
	if (ret == 0) {
		ret = vfs_fsconfig_locked(fc, cmd, &param);
		mutex_unlock(&fc->uapi_mutex);
	}

	/* Clean up the our record of any value that we obtained from
	 * userspace.  Note that the value may have been stolen by the LSM or
	 * filesystem, in which case the value pointer will have been cleared.
	 */
	switch (cmd) {
	case FSCONFIG_SET_STRING:
	case FSCONFIG_SET_BINARY:
		kfree(param.string);
		break;
	case FSCONFIG_SET_PATH:
	case FSCONFIG_SET_PATH_EMPTY:
		if (param.name)
			putname(param.name);
		break;
	case FSCONFIG_SET_FD:
		if (param.file)
			fput(param.file);
		break;
	default:
		break;
	}
out_key:
	kfree(param.key);
out_f:
	fdput(f);
	return ret;
}
Commit	Line	Data
b4d0d230	1	// SPDX-License-Identifier: GPL-2.0-or-later
24dcb3d9 DH	2	/* Filesystem access-by-fd.
	3	*
	4	* Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
	5	* Written by David Howells ([email protected])
24dcb3d9 DH	6	*/
	7
	8	#include <linux/fs_context.h>
ecdab150	9	#include <linux/fs_parser.h>
24dcb3d9 DH	10	#include <linux/slab.h>
	11	#include <linux/uaccess.h>
	12	#include <linux/syscalls.h>
	13	#include <linux/security.h>
	14	#include <linux/anon_inodes.h>
	15	#include <linux/namei.h>
	16	#include <linux/file.h>
	17	#include <uapi/linux/mount.h>
ecdab150	18	#include "internal.h"
24dcb3d9 DH	19	#include "mount.h"
24dcb3d9 DH	20
007ec26c DH	21	/*
	22	* Allow the user to read back any error, warning or informational messages.
	23	*/
	24	static ssize_t fscontext_read(struct file *file,
	25	char __user _buf, size_t len, loff_t pos)
	26	{
	27	struct fs_context *fc = file->private_data;
	28	struct fc_log *log = fc->log;
	29	unsigned int logsize = ARRAY_SIZE(log->buffer);
	30	ssize_t ret;
	31	char *p;
	32	bool need_free;
	33	int index, n;
	34
	35	ret = mutex_lock_interruptible(&fc->uapi_mutex);
	36	if (ret < 0)
	37	return ret;
	38
	39	if (log->head == log->tail) {
	40	mutex_unlock(&fc->uapi_mutex);
	41	return -ENODATA;
	42	}
	43
	44	index = log->tail & (logsize - 1);
	45	p = log->buffer[index];
	46	need_free = log->need_free & (1 << index);
	47	log->buffer[index] = NULL;
	48	log->need_free &= ~(1 << index);
	49	log->tail++;
	50	mutex_unlock(&fc->uapi_mutex);
	51
	52	ret = -EMSGSIZE;
	53	n = strlen(p);
	54	if (n > len)
	55	goto err_free;
	56	ret = -EFAULT;
	57	if (copy_to_user(_buf, p, n) != 0)
	58	goto err_free;
	59	ret = n;
	60
	61	err_free:
	62	if (need_free)
	63	kfree(p);
	64	return ret;
	65	}
	66
24dcb3d9 DH	67	static int fscontext_release(struct inode inode, struct file file)
	68	{
	69	struct fs_context *fc = file->private_data;
	70
	71	if (fc) {
	72	file->private_data = NULL;
	73	put_fs_context(fc);
	74	}
	75	return 0;
	76	}
	77
	78	const struct file_operations fscontext_fops = {
007ec26c	79	.read = fscontext_read,
24dcb3d9 DH	80	.release = fscontext_release,
	81	.llseek = no_llseek,
	82	};
	83
	84	/*
	85	* Attach a filesystem context to a file and an fd.
	86	*/
	87	static int fscontext_create_fd(struct fs_context *fc, unsigned int o_flags)
	88	{
	89	int fd;
	90
1cdc415f	91	fd = anon_inode_getfd("[fscontext]", &fscontext_fops, fc,
24dcb3d9 DH	92	O_RDWR \| o_flags);
	93	if (fd < 0)
	94	put_fs_context(fc);
	95	return fd;
	96	}
	97
007ec26c DH	98	static int fscontext_alloc_log(struct fs_context *fc)
	99	{
	100	fc->log = kzalloc(sizeof(*fc->log), GFP_KERNEL);
	101	if (!fc->log)
	102	return -ENOMEM;
	103	refcount_set(&fc->log->usage, 1);
	104	fc->log->owner = fc->fs_type->owner;
	105	return 0;
	106	}
	107
24dcb3d9 DH	108	/*
	109	* Open a filesystem by name so that it can be configured for mounting.
	110	*
	111	* We are allowed to specify a container in which the filesystem will be
	112	* opened, thereby indicating which namespaces will be used (notably, which
	113	* network namespace will be used for network filesystems).
	114	*/
	115	SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags)
	116	{
	117	struct file_system_type *fs_type;
	118	struct fs_context *fc;
	119	const char *fs_name;
007ec26c	120	int ret;
24dcb3d9 DH	121
	122	if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
	123	return -EPERM;
	124
	125	if (flags & ~FSOPEN_CLOEXEC)
	126	return -EINVAL;
	127
	128	fs_name = strndup_user(_fs_name, PAGE_SIZE);
	129	if (IS_ERR(fs_name))
	130	return PTR_ERR(fs_name);
	131
	132	fs_type = get_fs_type(fs_name);
	133	kfree(fs_name);
	134	if (!fs_type)
	135	return -ENODEV;
	136
	137	fc = fs_context_for_mount(fs_type, 0);
	138	put_filesystem(fs_type);
	139	if (IS_ERR(fc))
	140	return PTR_ERR(fc);
	141
	142	fc->phase = FS_CONTEXT_CREATE_PARAMS;
007ec26c DH	143
	144	ret = fscontext_alloc_log(fc);
	145	if (ret < 0)
	146	goto err_fc;
	147
24dcb3d9	148	return fscontext_create_fd(fc, flags & FSOPEN_CLOEXEC ? O_CLOEXEC : 0);
007ec26c DH	149
	150	err_fc:
	151	put_fs_context(fc);
	152	return ret;
24dcb3d9	153	}
ecdab150	154
cf3cba4a DH	155	/*
	156	* Pick a superblock into a context for reconfiguration.
	157	*/
	158	SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags)
	159	{
	160	struct fs_context *fc;
	161	struct path target;
	162	unsigned int lookup_flags;
	163	int ret;
	164
	165	if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
	166	return -EPERM;
	167
	168	if ((flags & ~(FSPICK_CLOEXEC \|
	169	FSPICK_SYMLINK_NOFOLLOW \|
	170	FSPICK_NO_AUTOMOUNT \|
	171	FSPICK_EMPTY_PATH)) != 0)
	172	return -EINVAL;
	173
	174	lookup_flags = LOOKUP_FOLLOW \| LOOKUP_AUTOMOUNT;
	175	if (flags & FSPICK_SYMLINK_NOFOLLOW)
	176	lookup_flags &= ~LOOKUP_FOLLOW;
	177	if (flags & FSPICK_NO_AUTOMOUNT)
	178	lookup_flags &= ~LOOKUP_AUTOMOUNT;
	179	if (flags & FSPICK_EMPTY_PATH)
	180	lookup_flags \|= LOOKUP_EMPTY;
	181	ret = user_path_at(dfd, path, lookup_flags, &target);
	182	if (ret < 0)
	183	goto err;
	184
	185	ret = -EINVAL;
	186	if (target.mnt->mnt_root != target.dentry)
	187	goto err_path;
	188
	189	fc = fs_context_for_reconfigure(target.dentry, 0, 0);
	190	if (IS_ERR(fc)) {
	191	ret = PTR_ERR(fc);
	192	goto err_path;
	193	}
	194
	195	fc->phase = FS_CONTEXT_RECONF_PARAMS;
	196
	197	ret = fscontext_alloc_log(fc);
	198	if (ret < 0)
	199	goto err_fc;
	200
	201	path_put(&target);
	202	return fscontext_create_fd(fc, flags & FSPICK_CLOEXEC ? O_CLOEXEC : 0);
	203
	204	err_fc:
	205	put_fs_context(fc);
	206	err_path:
	207	path_put(&target);
	208	err:
	209	return ret;
	210	}
	211
ecdab150 DH	212	/*
	213	* Check the state and apply the configuration. Note that this function is
	214	* allowed to 'steal' the value by setting param->xxx to NULL before returning.
	215	*/
	216	static int vfs_fsconfig_locked(struct fs_context *fc, int cmd,
	217	struct fs_parameter *param)
	218	{
	219	struct super_block *sb;
	220	int ret;
	221
	222	ret = finish_clean_context(fc);
	223	if (ret)
	224	return ret;
	225	switch (cmd) {
	226	case FSCONFIG_CMD_CREATE:
	227	if (fc->phase != FS_CONTEXT_CREATE_PARAMS)
	228	return -EBUSY;
	229	fc->phase = FS_CONTEXT_CREATING;
	230	ret = vfs_get_tree(fc);
	231	if (ret)
	232	break;
	233	sb = fc->root->d_sb;
	234	ret = security_sb_kern_mount(sb);
	235	if (unlikely(ret)) {
	236	fc_drop_locked(fc);
	237	break;
	238	}
	239	up_write(&sb->s_umount);
	240	fc->phase = FS_CONTEXT_AWAITING_MOUNT;
	241	return 0;
	242	case FSCONFIG_CMD_RECONFIGURE:
	243	if (fc->phase != FS_CONTEXT_RECONF_PARAMS)
	244	return -EBUSY;
	245	fc->phase = FS_CONTEXT_RECONFIGURING;
	246	sb = fc->root->d_sb;
	247	if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
	248	ret = -EPERM;
	249	break;
	250	}
	251	down_write(&sb->s_umount);
	252	ret = reconfigure_super(fc);
	253	up_write(&sb->s_umount);
	254	if (ret)
	255	break;
	256	vfs_clean_context(fc);
	257	return 0;
	258	default:
	259	if (fc->phase != FS_CONTEXT_CREATE_PARAMS &&
	260	fc->phase != FS_CONTEXT_RECONF_PARAMS)
	261	return -EBUSY;
	262
	263	return vfs_parse_fs_param(fc, param);
	264	}
	265	fc->phase = FS_CONTEXT_FAILED;
	266	return ret;
	267	}
	268
	269	/**
	270	* sys_fsconfig - Set parameters and trigger actions on a context
	271	* @fd: The filesystem context to act upon
	272	* @cmd: The action to take
	273	* @_key: Where appropriate, the parameter key to set
	274	* @_value: Where appropriate, the parameter value to set
	275	* @aux: Additional information for the value
276	*
277	* This system call is used to set parameters on a context, including
278	* superblock settings, data source and security labelling.
279	*
280	* Actions include triggering the creation of a superblock and the
281	* reconfiguration of the superblock attached to the specified context.
282	*
283	* When setting a parameter, @cmd indicates the type of value being proposed
284	* and @_key indicates the parameter to be altered.
285	*
286	* @_value and @aux are used to specify the value, should a value be required:
287	*
288	* (*) fsconfig_set_flag: No value is specified. The parameter must be boolean
289	* in nature. The key may be prefixed with "no" to invert the
290	* setting. @_value must be NULL and @aux must be 0.
291	*
292	* (*) fsconfig_set_string: A string value is specified. The parameter can be
293	* expecting boolean, integer, string or take a path. A conversion to an
294	* appropriate type will be attempted (which may include looking up as a
295	* path). @_value points to a NUL-terminated string and @aux must be 0.
296	*
297	* (*) fsconfig_set_binary: A binary blob is specified. @_value points to the
298	* blob and @aux indicates its size. The parameter must be expecting a
299	* blob.
300	*
301	* (*) fsconfig_set_path: A non-empty path is specified. The parameter must be
302	* expecting a path object. @_value points to a NUL-terminated string that
303	* is the path and @aux is a file descriptor at which to start a relative
304	* lookup or AT_FDCWD.
305	*
306	* (*) fsconfig_set_path_empty: As fsconfig_set_path, but with AT_EMPTY_PATH
307	* implied.
308	*
309	* (*) fsconfig_set_fd: An open file descriptor is specified. @_value must be
310	* NULL and @aux indicates the file descriptor.
311	*/
312	SYSCALL_DEFINE5(fsconfig,
313	int, fd,
314	unsigned int, cmd,
315	const char __user *, _key,
316	const void __user *, _value,
317	int, aux)
318	{
319	struct fs_context *fc;
320	struct fd f;
321	int ret;
322
323	struct fs_parameter param = {
324	.type = fs_value_is_undefined,
325	};
326
327	if (fd < 0)
328	return -EINVAL;
329
330	switch (cmd) {
331	case FSCONFIG_SET_FLAG:
332	if (!_key \|\| _value \|\| aux)
333	return -EINVAL;
334	break;
335	case FSCONFIG_SET_STRING:
336	if (!_key \|\| !_value \|\| aux)
337	return -EINVAL;
338	break;
339	case FSCONFIG_SET_BINARY:
340	if (!_key \|\| !_value \|\| aux <= 0 \|\| aux > 1024 * 1024)
341	return -EINVAL;
342	break;
343	case FSCONFIG_SET_PATH:
344	case FSCONFIG_SET_PATH_EMPTY:
345	if (!_key \|\| !_value \|\| (aux != AT_FDCWD && aux < 0))
346	return -EINVAL;
347	break;
348	case FSCONFIG_SET_FD:
349	if (!_key \|\| _value \|\| aux < 0)
350	return -EINVAL;
351	break;
352	case FSCONFIG_CMD_CREATE:
353	case FSCONFIG_CMD_RECONFIGURE:
354	if (_key \|\| _value \|\| aux)
355	return -EINVAL;
356	break;
357	default:
358	return -EOPNOTSUPP;
359	}
360
361	f = fdget(fd);
362	if (!f.file)
363	return -EBADF;
364	ret = -EINVAL;
365	if (f.file->f_op != &fscontext_fops)
366	goto out_f;
367
368	fc = f.file->private_data;
369	if (fc->ops == &legacy_fs_context_ops) {
370	switch (cmd) {
371	case FSCONFIG_SET_BINARY:
372	case FSCONFIG_SET_PATH:
373	case FSCONFIG_SET_PATH_EMPTY:
374	case FSCONFIG_SET_FD:
375	ret = -EOPNOTSUPP;
376	goto out_f;
377	}
378	}
379
380	if (_key) {
381	param.key = strndup_user(_key, 256);
382	if (IS_ERR(param.key)) {
383	ret = PTR_ERR(param.key);
384	goto out_f;
385	}
386	}
387
388	switch (cmd) {
389	case FSCONFIG_SET_FLAG:
390	param.type = fs_value_is_flag;
391	break;
392	case FSCONFIG_SET_STRING:
393	param.type = fs_value_is_string;
394	param.string = strndup_user(_value, 256);
395	if (IS_ERR(param.string)) {
396	ret = PTR_ERR(param.string);
397	goto out_key;
398	}
399	param.size = strlen(param.string);
400	break;
401	case FSCONFIG_SET_BINARY:
402	param.type = fs_value_is_blob;
403	param.size = aux;
404	param.blob = memdup_user_nul(_value, aux);
405	if (IS_ERR(param.blob)) {
406	ret = PTR_ERR(param.blob);
407	goto out_key;
408	}
409	break;
410	case FSCONFIG_SET_PATH:
411	param.type = fs_value_is_filename;
412	param.name = getname_flags(_value, 0, NULL);
413	if (IS_ERR(param.name)) {
414	ret = PTR_ERR(param.name);
415	goto out_key;
416	}
417	param.dirfd = aux;
418	param.size = strlen(param.name->name);
419	break;
420	case FSCONFIG_SET_PATH_EMPTY:
421	param.type = fs_value_is_filename_empty;
422	param.name = getname_flags(_value, LOOKUP_EMPTY, NULL);
423	if (IS_ERR(param.name)) {
424	ret = PTR_ERR(param.name);
425	goto out_key;
426	}
427	param.dirfd = aux;
428	param.size = strlen(param.name->name);
429	break;
430	case FSCONFIG_SET_FD:
431	param.type = fs_value_is_file;
432	ret = -EBADF;
433	param.file = fget(aux);
434	if (!param.file)
435	goto out_key;
436	break;
437	default:
438	break;
439	}
440
441	ret = mutex_lock_interruptible(&fc->uapi_mutex);
442	if (ret == 0) {
443	ret = vfs_fsconfig_locked(fc, cmd, &param);
444	mutex_unlock(&fc->uapi_mutex);
445	}
446
447	/* Clean up the our record of any value that we obtained from
448	* userspace. Note that the value may have been stolen by the LSM or
449	* filesystem, in which case the value pointer will have been cleared.
450	*/
451	switch (cmd) {
452	case FSCONFIG_SET_STRING:
453	case FSCONFIG_SET_BINARY:
454	kfree(param.string);
455	break;
456	case FSCONFIG_SET_PATH:
457	case FSCONFIG_SET_PATH_EMPTY:
458	if (param.name)
459	putname(param.name);
460	break;
461	case FSCONFIG_SET_FD:
462	if (param.file)
463	fput(param.file);
464	break;
465	default:
466	break;
467	}
468	out_key:
469	kfree(param.key);
470	out_f:
471	fdput(f);
472	return ret;
473	}