[linux.git] / fs / fsopen.c

/* Filesystem access-by-fd.
 *
 * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#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
24dcb3d9 DH	1	/* Filesystem access-by-fd.
	2	*
	3	* Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
	4	* Written by David Howells ([email protected])
	5	*
	6	* This program is free software; you can redistribute it and/or
	7	* modify it under the terms of the GNU General Public Licence
	8	* as published by the Free Software Foundation; either version
	9	* 2 of the Licence, or (at your option) any later version.
	10	*/
	11
	12	#include <linux/fs_context.h>
ecdab150	13	#include <linux/fs_parser.h>
24dcb3d9 DH	14	#include <linux/slab.h>
	15	#include <linux/uaccess.h>
	16	#include <linux/syscalls.h>
	17	#include <linux/security.h>
	18	#include <linux/anon_inodes.h>
	19	#include <linux/namei.h>
	20	#include <linux/file.h>
	21	#include <uapi/linux/mount.h>
ecdab150	22	#include "internal.h"
24dcb3d9 DH	23	#include "mount.h"
24dcb3d9 DH	24
007ec26c DH	25	/*
	26	* Allow the user to read back any error, warning or informational messages.
	27	*/
	28	static ssize_t fscontext_read(struct file *file,
	29	char __user _buf, size_t len, loff_t pos)
	30	{
	31	struct fs_context *fc = file->private_data;
	32	struct fc_log *log = fc->log;
	33	unsigned int logsize = ARRAY_SIZE(log->buffer);
	34	ssize_t ret;
	35	char *p;
	36	bool need_free;
	37	int index, n;
	38
	39	ret = mutex_lock_interruptible(&fc->uapi_mutex);
	40	if (ret < 0)
	41	return ret;
	42
	43	if (log->head == log->tail) {
	44	mutex_unlock(&fc->uapi_mutex);
	45	return -ENODATA;
	46	}
	47
	48	index = log->tail & (logsize - 1);
	49	p = log->buffer[index];
	50	need_free = log->need_free & (1 << index);
	51	log->buffer[index] = NULL;
	52	log->need_free &= ~(1 << index);
	53	log->tail++;
	54	mutex_unlock(&fc->uapi_mutex);
	55
	56	ret = -EMSGSIZE;
	57	n = strlen(p);
	58	if (n > len)
	59	goto err_free;
	60	ret = -EFAULT;
	61	if (copy_to_user(_buf, p, n) != 0)
	62	goto err_free;
	63	ret = n;
	64
	65	err_free:
	66	if (need_free)
	67	kfree(p);
	68	return ret;
	69	}
	70
24dcb3d9 DH	71	static int fscontext_release(struct inode inode, struct file file)
	72	{
	73	struct fs_context *fc = file->private_data;
	74
	75	if (fc) {
	76	file->private_data = NULL;
	77	put_fs_context(fc);
	78	}
	79	return 0;
	80	}
	81
	82	const struct file_operations fscontext_fops = {
007ec26c	83	.read = fscontext_read,
24dcb3d9 DH	84	.release = fscontext_release,
	85	.llseek = no_llseek,
	86	};
	87
	88	/*
	89	* Attach a filesystem context to a file and an fd.
	90	*/
	91	static int fscontext_create_fd(struct fs_context *fc, unsigned int o_flags)
	92	{
	93	int fd;
	94
1cdc415f	95	fd = anon_inode_getfd("[fscontext]", &fscontext_fops, fc,
24dcb3d9 DH	96	O_RDWR \| o_flags);
	97	if (fd < 0)
	98	put_fs_context(fc);
	99	return fd;
	100	}
	101
007ec26c DH	102	static int fscontext_alloc_log(struct fs_context *fc)
	103	{
	104	fc->log = kzalloc(sizeof(*fc->log), GFP_KERNEL);
	105	if (!fc->log)
	106	return -ENOMEM;
	107	refcount_set(&fc->log->usage, 1);
	108	fc->log->owner = fc->fs_type->owner;
	109	return 0;
	110	}
	111
24dcb3d9 DH	112	/*
	113	* Open a filesystem by name so that it can be configured for mounting.
	114	*
	115	* We are allowed to specify a container in which the filesystem will be
	116	* opened, thereby indicating which namespaces will be used (notably, which
	117	* network namespace will be used for network filesystems).
	118	*/
	119	SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags)
	120	{
	121	struct file_system_type *fs_type;
	122	struct fs_context *fc;
	123	const char *fs_name;
007ec26c	124	int ret;
24dcb3d9 DH	125
	126	if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
	127	return -EPERM;
	128
	129	if (flags & ~FSOPEN_CLOEXEC)
	130	return -EINVAL;
	131
	132	fs_name = strndup_user(_fs_name, PAGE_SIZE);
	133	if (IS_ERR(fs_name))
	134	return PTR_ERR(fs_name);
	135
	136	fs_type = get_fs_type(fs_name);
	137	kfree(fs_name);
	138	if (!fs_type)
	139	return -ENODEV;
	140
	141	fc = fs_context_for_mount(fs_type, 0);
	142	put_filesystem(fs_type);
	143	if (IS_ERR(fc))
	144	return PTR_ERR(fc);
	145
	146	fc->phase = FS_CONTEXT_CREATE_PARAMS;
007ec26c DH	147
	148	ret = fscontext_alloc_log(fc);
	149	if (ret < 0)
	150	goto err_fc;
	151
24dcb3d9	152	return fscontext_create_fd(fc, flags & FSOPEN_CLOEXEC ? O_CLOEXEC : 0);
007ec26c DH	153
	154	err_fc:
	155	put_fs_context(fc);
	156	return ret;
24dcb3d9	157	}
ecdab150	158
cf3cba4a DH	159	/*
	160	* Pick a superblock into a context for reconfiguration.
	161	*/
	162	SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags)
	163	{
	164	struct fs_context *fc;
	165	struct path target;
	166	unsigned int lookup_flags;
	167	int ret;
	168
	169	if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
	170	return -EPERM;
	171
	172	if ((flags & ~(FSPICK_CLOEXEC \|
	173	FSPICK_SYMLINK_NOFOLLOW \|
	174	FSPICK_NO_AUTOMOUNT \|
	175	FSPICK_EMPTY_PATH)) != 0)
	176	return -EINVAL;
	177
	178	lookup_flags = LOOKUP_FOLLOW \| LOOKUP_AUTOMOUNT;
	179	if (flags & FSPICK_SYMLINK_NOFOLLOW)
	180	lookup_flags &= ~LOOKUP_FOLLOW;
	181	if (flags & FSPICK_NO_AUTOMOUNT)
	182	lookup_flags &= ~LOOKUP_AUTOMOUNT;
	183	if (flags & FSPICK_EMPTY_PATH)
	184	lookup_flags \|= LOOKUP_EMPTY;
	185	ret = user_path_at(dfd, path, lookup_flags, &target);
	186	if (ret < 0)
	187	goto err;
	188
	189	ret = -EINVAL;
	190	if (target.mnt->mnt_root != target.dentry)
	191	goto err_path;
	192
	193	fc = fs_context_for_reconfigure(target.dentry, 0, 0);
	194	if (IS_ERR(fc)) {
	195	ret = PTR_ERR(fc);
	196	goto err_path;
	197	}
	198
	199	fc->phase = FS_CONTEXT_RECONF_PARAMS;
	200
	201	ret = fscontext_alloc_log(fc);
	202	if (ret < 0)
	203	goto err_fc;
	204
	205	path_put(&target);
	206	return fscontext_create_fd(fc, flags & FSPICK_CLOEXEC ? O_CLOEXEC : 0);
	207
	208	err_fc:
	209	put_fs_context(fc);
	210	err_path:
	211	path_put(&target);
	212	err:
	213	return ret;
	214	}
	215
ecdab150 DH	216	/*
	217	* Check the state and apply the configuration. Note that this function is
	218	* allowed to 'steal' the value by setting param->xxx to NULL before returning.
	219	*/
	220	static int vfs_fsconfig_locked(struct fs_context *fc, int cmd,
	221	struct fs_parameter *param)
	222	{
	223	struct super_block *sb;
	224	int ret;
	225
	226	ret = finish_clean_context(fc);
	227	if (ret)
	228	return ret;
	229	switch (cmd) {
	230	case FSCONFIG_CMD_CREATE:
	231	if (fc->phase != FS_CONTEXT_CREATE_PARAMS)
	232	return -EBUSY;
	233	fc->phase = FS_CONTEXT_CREATING;
	234	ret = vfs_get_tree(fc);
	235	if (ret)
	236	break;
	237	sb = fc->root->d_sb;
	238	ret = security_sb_kern_mount(sb);
	239	if (unlikely(ret)) {
	240	fc_drop_locked(fc);
	241	break;
	242	}
	243	up_write(&sb->s_umount);
	244	fc->phase = FS_CONTEXT_AWAITING_MOUNT;
	245	return 0;
	246	case FSCONFIG_CMD_RECONFIGURE:
	247	if (fc->phase != FS_CONTEXT_RECONF_PARAMS)
	248	return -EBUSY;
	249	fc->phase = FS_CONTEXT_RECONFIGURING;
	250	sb = fc->root->d_sb;
	251	if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
	252	ret = -EPERM;
	253	break;
	254	}
	255	down_write(&sb->s_umount);
	256	ret = reconfigure_super(fc);
	257	up_write(&sb->s_umount);
	258	if (ret)
	259	break;
	260	vfs_clean_context(fc);
	261	return 0;
	262	default:
	263	if (fc->phase != FS_CONTEXT_CREATE_PARAMS &&
	264	fc->phase != FS_CONTEXT_RECONF_PARAMS)
	265	return -EBUSY;
	266
	267	return vfs_parse_fs_param(fc, param);
	268	}
	269	fc->phase = FS_CONTEXT_FAILED;
	270	return ret;
	271	}
	272
	273	/**
	274	* sys_fsconfig - Set parameters and trigger actions on a context
	275	* @fd: The filesystem context to act upon
	276	* @cmd: The action to take
	277	* @_key: Where appropriate, the parameter key to set
	278	* @_value: Where appropriate, the parameter value to set
	279	* @aux: Additional information for the value
280	*
281	* This system call is used to set parameters on a context, including
282	* superblock settings, data source and security labelling.
283	*
284	* Actions include triggering the creation of a superblock and the
285	* reconfiguration of the superblock attached to the specified context.
286	*
287	* When setting a parameter, @cmd indicates the type of value being proposed
288	* and @_key indicates the parameter to be altered.
289	*
290	* @_value and @aux are used to specify the value, should a value be required:
291	*
292	* (*) fsconfig_set_flag: No value is specified. The parameter must be boolean
293	* in nature. The key may be prefixed with "no" to invert the
294	* setting. @_value must be NULL and @aux must be 0.
295	*
296	* (*) fsconfig_set_string: A string value is specified. The parameter can be
297	* expecting boolean, integer, string or take a path. A conversion to an
298	* appropriate type will be attempted (which may include looking up as a
299	* path). @_value points to a NUL-terminated string and @aux must be 0.
300	*
301	* (*) fsconfig_set_binary: A binary blob is specified. @_value points to the
302	* blob and @aux indicates its size. The parameter must be expecting a
303	* blob.
304	*
305	* (*) fsconfig_set_path: A non-empty path is specified. The parameter must be
306	* expecting a path object. @_value points to a NUL-terminated string that
307	* is the path and @aux is a file descriptor at which to start a relative
308	* lookup or AT_FDCWD.
309	*
310	* (*) fsconfig_set_path_empty: As fsconfig_set_path, but with AT_EMPTY_PATH
311	* implied.
312	*
313	* (*) fsconfig_set_fd: An open file descriptor is specified. @_value must be
314	* NULL and @aux indicates the file descriptor.
315	*/
316	SYSCALL_DEFINE5(fsconfig,
317	int, fd,
318	unsigned int, cmd,
319	const char __user *, _key,
320	const void __user *, _value,
321	int, aux)
322	{
323	struct fs_context *fc;
324	struct fd f;
325	int ret;
326
327	struct fs_parameter param = {
328	.type = fs_value_is_undefined,
329	};
330
331	if (fd < 0)
332	return -EINVAL;
333
334	switch (cmd) {
335	case FSCONFIG_SET_FLAG:
336	if (!_key \|\| _value \|\| aux)
337	return -EINVAL;
338	break;
339	case FSCONFIG_SET_STRING:
340	if (!_key \|\| !_value \|\| aux)
341	return -EINVAL;
342	break;
343	case FSCONFIG_SET_BINARY:
344	if (!_key \|\| !_value \|\| aux <= 0 \|\| aux > 1024 * 1024)
345	return -EINVAL;
346	break;
347	case FSCONFIG_SET_PATH:
348	case FSCONFIG_SET_PATH_EMPTY:
349	if (!_key \|\| !_value \|\| (aux != AT_FDCWD && aux < 0))
350	return -EINVAL;
351	break;
352	case FSCONFIG_SET_FD:
353	if (!_key \|\| _value \|\| aux < 0)
354	return -EINVAL;
355	break;
356	case FSCONFIG_CMD_CREATE:
357	case FSCONFIG_CMD_RECONFIGURE:
358	if (_key \|\| _value \|\| aux)
359	return -EINVAL;
360	break;
361	default:
362	return -EOPNOTSUPP;
363	}
364
365	f = fdget(fd);
366	if (!f.file)
367	return -EBADF;
368	ret = -EINVAL;
369	if (f.file->f_op != &fscontext_fops)
370	goto out_f;
371
372	fc = f.file->private_data;
373	if (fc->ops == &legacy_fs_context_ops) {
374	switch (cmd) {
375	case FSCONFIG_SET_BINARY:
376	case FSCONFIG_SET_PATH:
377	case FSCONFIG_SET_PATH_EMPTY:
378	case FSCONFIG_SET_FD:
379	ret = -EOPNOTSUPP;
380	goto out_f;
381	}
382	}
383
384	if (_key) {
385	param.key = strndup_user(_key, 256);
386	if (IS_ERR(param.key)) {
387	ret = PTR_ERR(param.key);
388	goto out_f;
389	}
390	}
391
392	switch (cmd) {
393	case FSCONFIG_SET_FLAG:
394	param.type = fs_value_is_flag;
395	break;
396	case FSCONFIG_SET_STRING:
397	param.type = fs_value_is_string;
398	param.string = strndup_user(_value, 256);
399	if (IS_ERR(param.string)) {
400	ret = PTR_ERR(param.string);
401	goto out_key;
402	}
403	param.size = strlen(param.string);
404	break;
405	case FSCONFIG_SET_BINARY:
406	param.type = fs_value_is_blob;
407	param.size = aux;
408	param.blob = memdup_user_nul(_value, aux);
409	if (IS_ERR(param.blob)) {
410	ret = PTR_ERR(param.blob);
411	goto out_key;
412	}
413	break;
414	case FSCONFIG_SET_PATH:
415	param.type = fs_value_is_filename;
416	param.name = getname_flags(_value, 0, NULL);
417	if (IS_ERR(param.name)) {
418	ret = PTR_ERR(param.name);
419	goto out_key;
420	}
421	param.dirfd = aux;
422	param.size = strlen(param.name->name);
423	break;
424	case FSCONFIG_SET_PATH_EMPTY:
425	param.type = fs_value_is_filename_empty;
426	param.name = getname_flags(_value, LOOKUP_EMPTY, NULL);
427	if (IS_ERR(param.name)) {
428	ret = PTR_ERR(param.name);
429	goto out_key;
430	}
431	param.dirfd = aux;
432	param.size = strlen(param.name->name);
433	break;
434	case FSCONFIG_SET_FD:
435	param.type = fs_value_is_file;
436	ret = -EBADF;
437	param.file = fget(aux);
438	if (!param.file)
439	goto out_key;
440	break;
441	default:
442	break;
443	}
444
445	ret = mutex_lock_interruptible(&fc->uapi_mutex);
446	if (ret == 0) {
447	ret = vfs_fsconfig_locked(fc, cmd, &param);
448	mutex_unlock(&fc->uapi_mutex);
449	}
450
451	/* Clean up the our record of any value that we obtained from
452	* userspace. Note that the value may have been stolen by the LSM or
453	* filesystem, in which case the value pointer will have been cleared.
454	*/
455	switch (cmd) {
456	case FSCONFIG_SET_STRING:
457	case FSCONFIG_SET_BINARY:
458	kfree(param.string);
459	break;
460	case FSCONFIG_SET_PATH:
461	case FSCONFIG_SET_PATH_EMPTY:
462	if (param.name)
463	putname(param.name);
464	break;
465	case FSCONFIG_SET_FD:
466	if (param.file)
467	fput(param.file);
468	break;
469	default:
470	break;
471	}
472	out_key:
473	kfree(param.key);
474	out_f:
475	fdput(f);
476	return ret;
477	}