fs/fhandle.c - third_party/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 #include <linux/syscalls.h>
 #include <linux/slab.h>
 #include <linux/fs.h>
 #include <linux/file.h>
 #include <linux/mount.h>
 #include <linux/namei.h>
 #include <linux/exportfs.h>
 #include <linux/fs_struct.h>
 #include <linux/fsnotify.h>
 #include <linux/personality.h>
 #include <linux/uaccess.h>
 #include <linux/compat.h>
 #include "internal.h"
 #include "mount.h"

 static long do_sys_name_to_handle(const struct path *path,
 				  struct file_handle __user *ufh,
 				  void __user *mnt_id, bool unique_mntid,
 				  int fh_flags)
 {
 	long retval;
 	struct file_handle f_handle;
 	int handle_dwords, handle_bytes;
 	struct file_handle *handle = NULL;

 	/*
 	 * We need to make sure whether the file system support decoding of
 	 * the file handle if decodeable file handle was requested.
 	 */
 	if (!exportfs_can_encode_fh(path->dentry->d_sb->s_export_op, fh_flags))
 		return -EOPNOTSUPP;

 	if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
 		return -EFAULT;

 	if (f_handle.handle_bytes > MAX_HANDLE_SZ)
 		return -EINVAL;

 	handle = kzalloc(struct_size(handle, f_handle, f_handle.handle_bytes),
 			 GFP_KERNEL);
 	if (!handle)
 		return -ENOMEM;

 	/* convert handle size to multiple of sizeof(u32) */
 	handle_dwords = f_handle.handle_bytes >> 2;

 	/* we ask for a non connectable maybe decodeable file handle */
 	retval = exportfs_encode_fh(path->dentry,
 				    (struct fid *)handle->f_handle,
 				    &handle_dwords, fh_flags);
 	handle->handle_type = retval;
 	/* convert handle size to bytes */
 	handle_bytes = handle_dwords * sizeof(u32);
 	handle->handle_bytes = handle_bytes;
 	if ((handle->handle_bytes > f_handle.handle_bytes) ||
 	    (retval == FILEID_INVALID) || (retval < 0)) {
 		/* As per old exportfs_encode_fh documentation
 		 * we could return ENOSPC to indicate overflow
 		 * But file system returned 255 always. So handle
 		 * both the values
 		 */
 		if (retval == FILEID_INVALID || retval == -ENOSPC)
 			retval = -EOVERFLOW;
 		/*
 		 * set the handle size to zero so we copy only
 		 * non variable part of the file_handle
 		 */
 		handle_bytes = 0;
 	} else
 		retval = 0;
 	/* copy the mount id */
 	if (unique_mntid) {
 		if (put_user(real_mount(path->mnt)->mnt_id_unique,
 			     (u64 __user *) mnt_id))
 			retval = -EFAULT;
 	} else {
 		if (put_user(real_mount(path->mnt)->mnt_id,
 			     (int __user *) mnt_id))
 			retval = -EFAULT;
 	}
 	/* copy the handle */
 	if (retval != -EFAULT &&
 		copy_to_user(ufh, handle,
 			     struct_size(handle, f_handle, handle_bytes)))
 		retval = -EFAULT;
 	kfree(handle);
 	return retval;
 }

 /**
  * sys_name_to_handle_at: convert name to handle
  * @dfd: directory relative to which name is interpreted if not absolute
  * @name: name that should be converted to handle.
  * @handle: resulting file handle
  * @mnt_id: mount id of the file system containing the file
  *          (u64 if AT_HANDLE_MNT_ID_UNIQUE, otherwise int)
  * @flag: flag value to indicate whether to follow symlink or not
  *        and whether a decodable file handle is required.
  *
  * @handle->handle_size indicate the space available to store the
  * variable part of the file handle in bytes. If there is not
  * enough space, the field is updated to return the minimum
  * value required.
  */
 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
 		struct file_handle __user *, handle, void __user *, mnt_id,
 		int, flag)
 {
 	struct path path;
 	int lookup_flags;
 	int fh_flags;
 	int err;

 	if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID |
 		     AT_HANDLE_MNT_ID_UNIQUE))
 		return -EINVAL;

 	lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
 	fh_flags = (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0;
 	if (flag & AT_EMPTY_PATH)
 		lookup_flags |= LOOKUP_EMPTY;
 	err = user_path_at(dfd, name, lookup_flags, &path);
 	if (!err) {
 		err = do_sys_name_to_handle(&path, handle, mnt_id,
 					    flag & AT_HANDLE_MNT_ID_UNIQUE,
 					    fh_flags);
 		path_put(&path);
 	}
 	return err;
 }

 static int get_path_from_fd(int fd, struct path *root)
 {
 	if (fd == AT_FDCWD) {
 		struct fs_struct *fs = current->fs;
 		spin_lock(&fs->lock);
 		*root = fs->pwd;
 		path_get(root);
 		spin_unlock(&fs->lock);
 	} else {
 		CLASS(fd, f)(fd);
 		if (fd_empty(f))
 			return -EBADF;
 		*root = fd_file(f)->f_path;
 		path_get(root);
 	}

 	return 0;
 }

 enum handle_to_path_flags {
 	HANDLE_CHECK_PERMS   = (1 << 0),
 	HANDLE_CHECK_SUBTREE = (1 << 1),
 };

 struct handle_to_path_ctx {
 	struct path root;
 	enum handle_to_path_flags flags;
 	unsigned int fh_flags;
 };

 static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
 {
 	struct handle_to_path_ctx *ctx = context;
 	struct user_namespace *user_ns = current_user_ns();
 	struct dentry *d, *root = ctx->root.dentry;
 	struct mnt_idmap *idmap = mnt_idmap(ctx->root.mnt);
 	int retval = 0;

 	if (!root)
 		return 1;

 	/* Old permission model with global CAP_DAC_READ_SEARCH. */
 	if (!ctx->flags)
 		return 1;

 	/*
 	 * It's racy as we're not taking rename_lock but we're able to ignore
 	 * permissions and we just need an approximation whether we were able
 	 * to follow a path to the file.
 	 *
 	 * It's also potentially expensive on some filesystems especially if
 	 * there is a deep path.
 	 */
 	d = dget(dentry);
 	while (d != root && !IS_ROOT(d)) {
 		struct dentry *parent = dget_parent(d);

 		/*
 		 * We know that we have the ability to override DAC permissions
 		 * as we've verified this earlier via CAP_DAC_READ_SEARCH. But
 		 * we also need to make sure that there aren't any unmapped
 		 * inodes in the path that would prevent us from reaching the
 		 * file.
 		 */
 		if (!privileged_wrt_inode_uidgid(user_ns, idmap,
 						 d_inode(parent))) {
 			dput(d);
 			dput(parent);
 			return retval;
 		}

 		dput(d);
 		d = parent;
 	}

 	if (!(ctx->flags & HANDLE_CHECK_SUBTREE) || d == root)
 		retval = 1;
 	WARN_ON_ONCE(d != root && d != root->d_sb->s_root);
 	dput(d);
 	return retval;
 }

 static int do_handle_to_path(struct file_handle *handle, struct path *path,
 			     struct handle_to_path_ctx *ctx)
 {
 	int handle_dwords;
 	struct vfsmount *mnt = ctx->root.mnt;

 	/* change the handle size to multiple of sizeof(u32) */
 	handle_dwords = handle->handle_bytes >> 2;
 	path->dentry = exportfs_decode_fh_raw(mnt,
 					  (struct fid *)handle->f_handle,
 					  handle_dwords, handle->handle_type,
 					  ctx->fh_flags,
 					  vfs_dentry_acceptable, ctx);
 	if (IS_ERR_OR_NULL(path->dentry)) {
 		if (path->dentry == ERR_PTR(-ENOMEM))
 			return -ENOMEM;
 		return -ESTALE;
 	}
 	path->mnt = mntget(mnt);
 	return 0;
 }

 /*
  * Allow relaxed permissions of file handles if the caller has the
  * ability to mount the filesystem or create a bind-mount of the
  * provided @mountdirfd.
  *
  * In both cases the caller may be able to get an unobstructed way to
  * the encoded file handle. If the caller is only able to create a
  * bind-mount we need to verify that there are no locked mounts on top
  * of it that could prevent us from getting to the encoded file.
  *
  * In principle, locked mounts can prevent the caller from mounting the
  * filesystem but that only applies to procfs and sysfs neither of which
  * support decoding file handles.
  */
 static inline bool may_decode_fh(struct handle_to_path_ctx *ctx,
 				 unsigned int o_flags)
 {
 	struct path *root = &ctx->root;

 	/*
 	 * Restrict to O_DIRECTORY to provide a deterministic API that avoids a
 	 * confusing api in the face of disconnected non-dir dentries.
 	 *
 	 * There's only one dentry for each directory inode (VFS rule)...
 	 */
 	if (!(o_flags & O_DIRECTORY))
 		return false;

 	if (ns_capable(root->mnt->mnt_sb->s_user_ns, CAP_SYS_ADMIN))
 		ctx->flags = HANDLE_CHECK_PERMS;
 	else if (is_mounted(root->mnt) &&
 		 ns_capable(real_mount(root->mnt)->mnt_ns->user_ns,
 			    CAP_SYS_ADMIN) &&
 		 !has_locked_children(real_mount(root->mnt), root->dentry))
 		ctx->flags = HANDLE_CHECK_PERMS | HANDLE_CHECK_SUBTREE;
 	else
 		return false;

 	/* Are we able to override DAC permissions? */
 	if (!ns_capable(current_user_ns(), CAP_DAC_READ_SEARCH))
 		return false;

 	ctx->fh_flags = EXPORT_FH_DIR_ONLY;
 	return true;
 }

 static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
 		   struct path *path, unsigned int o_flags)
 {
 	int retval = 0;
 	struct file_handle f_handle;
 	struct file_handle *handle = NULL;
 	struct handle_to_path_ctx ctx = {};

 	retval = get_path_from_fd(mountdirfd, &ctx.root);
 	if (retval)
 		goto out_err;

 	if (!capable(CAP_DAC_READ_SEARCH) && !may_decode_fh(&ctx, o_flags)) {
 		retval = -EPERM;
 		goto out_path;
 	}

 	if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
 		retval = -EFAULT;
 		goto out_path;
 	}
 	if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
 	    (f_handle.handle_bytes == 0)) {
 		retval = -EINVAL;
 		goto out_path;
 	}
 	handle = kmalloc(struct_size(handle, f_handle, f_handle.handle_bytes),
 			 GFP_KERNEL);
 	if (!handle) {
 		retval = -ENOMEM;
 		goto out_path;
 	}
 	/* copy the full handle */
 	*handle = f_handle;
 	if (copy_from_user(&handle->f_handle,
 			   &ufh->f_handle,
 			   f_handle.handle_bytes)) {
 		retval = -EFAULT;
 		goto out_handle;
 	}

 	retval = do_handle_to_path(handle, path, &ctx);

 out_handle:
 	kfree(handle);
 out_path:
 	path_put(&ctx.root);
 out_err:
 	return retval;
 }

 static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
 			   int open_flag)
 {
 	long retval = 0;
 	struct path path;
 	struct file *file;
 	int fd;

 	retval = handle_to_path(mountdirfd, ufh, &path, open_flag);
 	if (retval)
 		return retval;

 	fd = get_unused_fd_flags(open_flag);
 	if (fd < 0) {
 		path_put(&path);
 		return fd;
 	}
 	file = file_open_root(&path, "", open_flag, 0);
 	if (IS_ERR(file)) {
 		put_unused_fd(fd);
 		retval =  PTR_ERR(file);
 	} else {
 		retval = fd;
 		fd_install(fd, file);
 	}
 	path_put(&path);
 	return retval;
 }

 /**
  * sys_open_by_handle_at: Open the file handle
  * @mountdirfd: directory file descriptor
  * @handle: file handle to be opened
  * @flags: open flags.
  *
  * @mountdirfd indicate the directory file descriptor
  * of the mount point. file handle is decoded relative
  * to the vfsmount pointed by the @mountdirfd. @flags
  * value is same as the open(2) flags.
  */
 SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
 		struct file_handle __user *, handle,
 		int, flags)
 {
 	long ret;

 	if (force_o_largefile())
 		flags |= O_LARGEFILE;

 	ret = do_handle_open(mountdirfd, handle, flags);
 	return ret;
 }

 #ifdef CONFIG_COMPAT
 /*
  * Exactly like fs/open.c:sys_open_by_handle_at(), except that it
  * doesn't set the O_LARGEFILE flag.
  */
 COMPAT_SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
 			     struct file_handle __user *, handle, int, flags)
 {
 	return do_handle_open(mountdirfd, handle, flags);
 }
 #endif
	// SPDX-License-Identifier: GPL-2.0
	#include <linux/syscalls.h>
	#include <linux/slab.h>
	#include <linux/fs.h>
	#include <linux/file.h>
	#include <linux/mount.h>
	#include <linux/namei.h>
	#include <linux/exportfs.h>
	#include <linux/fs_struct.h>
	#include <linux/fsnotify.h>
	#include <linux/personality.h>
	#include <linux/uaccess.h>
	#include <linux/compat.h>
	#include "internal.h"
	#include "mount.h"

	static long do_sys_name_to_handle(const struct path *path,
	struct file_handle __user *ufh,
	void __user *mnt_id, bool unique_mntid,
	int fh_flags)
	{
	long retval;
	struct file_handle f_handle;
	int handle_dwords, handle_bytes;
	struct file_handle *handle = NULL;

	/*
	* We need to make sure whether the file system support decoding of
	* the file handle if decodeable file handle was requested.
	*/
	if (!exportfs_can_encode_fh(path->dentry->d_sb->s_export_op, fh_flags))
	return -EOPNOTSUPP;

	if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
	return -EFAULT;

	if (f_handle.handle_bytes > MAX_HANDLE_SZ)
	return -EINVAL;

	handle = kzalloc(struct_size(handle, f_handle, f_handle.handle_bytes),
	GFP_KERNEL);
	if (!handle)
	return -ENOMEM;

	/* convert handle size to multiple of sizeof(u32) */
	handle_dwords = f_handle.handle_bytes >> 2;

	/* we ask for a non connectable maybe decodeable file handle */
	retval = exportfs_encode_fh(path->dentry,
	(struct fid *)handle->f_handle,
	&handle_dwords, fh_flags);
	handle->handle_type = retval;
	/* convert handle size to bytes */
	handle_bytes = handle_dwords * sizeof(u32);
	handle->handle_bytes = handle_bytes;
	if ((handle->handle_bytes > f_handle.handle_bytes) \|\|
	(retval == FILEID_INVALID) \|\| (retval < 0)) {
	/* As per old exportfs_encode_fh documentation
	* we could return ENOSPC to indicate overflow
	* But file system returned 255 always. So handle
	* both the values
	*/
	if (retval == FILEID_INVALID \|\| retval == -ENOSPC)
	retval = -EOVERFLOW;
	/*
	* set the handle size to zero so we copy only
	* non variable part of the file_handle
	*/
	handle_bytes = 0;
	} else
	retval = 0;
	/* copy the mount id */
	if (unique_mntid) {
	if (put_user(real_mount(path->mnt)->mnt_id_unique,
	(u64 __user *) mnt_id))
	retval = -EFAULT;
	} else {
	if (put_user(real_mount(path->mnt)->mnt_id,
	(int __user *) mnt_id))
	retval = -EFAULT;
	}
	/* copy the handle */
	if (retval != -EFAULT &&
	copy_to_user(ufh, handle,
	struct_size(handle, f_handle, handle_bytes)))
	retval = -EFAULT;
	kfree(handle);
	return retval;
	}

	/**
	* sys_name_to_handle_at: convert name to handle
	* @dfd: directory relative to which name is interpreted if not absolute
	* @name: name that should be converted to handle.
	* @handle: resulting file handle
	* @mnt_id: mount id of the file system containing the file
	* (u64 if AT_HANDLE_MNT_ID_UNIQUE, otherwise int)
	* @flag: flag value to indicate whether to follow symlink or not
	* and whether a decodable file handle is required.
	*
	* @handle->handle_size indicate the space available to store the
	* variable part of the file handle in bytes. If there is not
	* enough space, the field is updated to return the minimum
	* value required.
	*/
	SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
	struct file_handle __user , handle, void __user , mnt_id,
	int, flag)
	{
	struct path path;
	int lookup_flags;
	int fh_flags;
	int err;

	if (flag & ~(AT_SYMLINK_FOLLOW \| AT_EMPTY_PATH \| AT_HANDLE_FID \|
	AT_HANDLE_MNT_ID_UNIQUE))
	return -EINVAL;

	lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
	fh_flags = (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0;
	if (flag & AT_EMPTY_PATH)
	lookup_flags \|= LOOKUP_EMPTY;
	err = user_path_at(dfd, name, lookup_flags, &path);
	if (!err) {
	err = do_sys_name_to_handle(&path, handle, mnt_id,
	flag & AT_HANDLE_MNT_ID_UNIQUE,
	fh_flags);
	path_put(&path);
	}
	return err;
	}

	static int get_path_from_fd(int fd, struct path *root)
	{
	if (fd == AT_FDCWD) {
	struct fs_struct *fs = current->fs;
	spin_lock(&fs->lock);
	*root = fs->pwd;
	path_get(root);
	spin_unlock(&fs->lock);
	} else {
	CLASS(fd, f)(fd);
	if (fd_empty(f))
	return -EBADF;
	*root = fd_file(f)->f_path;
	path_get(root);
	}

	return 0;
	}

	enum handle_to_path_flags {
	HANDLE_CHECK_PERMS = (1 << 0),
	HANDLE_CHECK_SUBTREE = (1 << 1),
	};

	struct handle_to_path_ctx {
	struct path root;
	enum handle_to_path_flags flags;
	unsigned int fh_flags;
	};

	static int vfs_dentry_acceptable(void context, struct dentry dentry)
	{
	struct handle_to_path_ctx *ctx = context;
	struct user_namespace *user_ns = current_user_ns();
	struct dentry d, root = ctx->root.dentry;
	struct mnt_idmap *idmap = mnt_idmap(ctx->root.mnt);
	int retval = 0;

	if (!root)
	return 1;

	/* Old permission model with global CAP_DAC_READ_SEARCH. */
	if (!ctx->flags)
	return 1;

	/*
	* It's racy as we're not taking rename_lock but we're able to ignore
	* permissions and we just need an approximation whether we were able
	* to follow a path to the file.
	*
	* It's also potentially expensive on some filesystems especially if
	* there is a deep path.
	*/
	d = dget(dentry);
	while (d != root && !IS_ROOT(d)) {
	struct dentry *parent = dget_parent(d);

	/*
	* We know that we have the ability to override DAC permissions
	* as we've verified this earlier via CAP_DAC_READ_SEARCH. But
	* we also need to make sure that there aren't any unmapped
	* inodes in the path that would prevent us from reaching the
	* file.
	*/
	if (!privileged_wrt_inode_uidgid(user_ns, idmap,
	d_inode(parent))) {
	dput(d);
	dput(parent);
	return retval;
	}

	dput(d);
	d = parent;
	}

	if (!(ctx->flags & HANDLE_CHECK_SUBTREE) \|\| d == root)
	retval = 1;
	WARN_ON_ONCE(d != root && d != root->d_sb->s_root);
	dput(d);
	return retval;
	}

	static int do_handle_to_path(struct file_handle handle, struct path path,
	struct handle_to_path_ctx *ctx)
	{
	int handle_dwords;
	struct vfsmount *mnt = ctx->root.mnt;

	/* change the handle size to multiple of sizeof(u32) */
	handle_dwords = handle->handle_bytes >> 2;
	path->dentry = exportfs_decode_fh_raw(mnt,
	(struct fid *)handle->f_handle,
	handle_dwords, handle->handle_type,
	ctx->fh_flags,
	vfs_dentry_acceptable, ctx);
	if (IS_ERR_OR_NULL(path->dentry)) {
	if (path->dentry == ERR_PTR(-ENOMEM))
	return -ENOMEM;
	return -ESTALE;
	}
	path->mnt = mntget(mnt);
	return 0;
	}

	/*
	* Allow relaxed permissions of file handles if the caller has the
	* ability to mount the filesystem or create a bind-mount of the
	* provided @mountdirfd.
	*
	* In both cases the caller may be able to get an unobstructed way to
	* the encoded file handle. If the caller is only able to create a
	* bind-mount we need to verify that there are no locked mounts on top
	* of it that could prevent us from getting to the encoded file.
	*
	* In principle, locked mounts can prevent the caller from mounting the
	* filesystem but that only applies to procfs and sysfs neither of which
	* support decoding file handles.
	*/
	static inline bool may_decode_fh(struct handle_to_path_ctx *ctx,
	unsigned int o_flags)
	{
	struct path *root = &ctx->root;

	/*
	* Restrict to O_DIRECTORY to provide a deterministic API that avoids a
	* confusing api in the face of disconnected non-dir dentries.
	*
	* There's only one dentry for each directory inode (VFS rule)...
	*/
	if (!(o_flags & O_DIRECTORY))
	return false;

	if (ns_capable(root->mnt->mnt_sb->s_user_ns, CAP_SYS_ADMIN))
	ctx->flags = HANDLE_CHECK_PERMS;
	else if (is_mounted(root->mnt) &&
	ns_capable(real_mount(root->mnt)->mnt_ns->user_ns,
	CAP_SYS_ADMIN) &&
	!has_locked_children(real_mount(root->mnt), root->dentry))
	ctx->flags = HANDLE_CHECK_PERMS \| HANDLE_CHECK_SUBTREE;
	else
	return false;

	/* Are we able to override DAC permissions? */
	if (!ns_capable(current_user_ns(), CAP_DAC_READ_SEARCH))
	return false;

	ctx->fh_flags = EXPORT_FH_DIR_ONLY;
	return true;
	}

	static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
	struct path *path, unsigned int o_flags)
	{
	int retval = 0;
	struct file_handle f_handle;
	struct file_handle *handle = NULL;
	struct handle_to_path_ctx ctx = {};

	retval = get_path_from_fd(mountdirfd, &ctx.root);
	if (retval)
	goto out_err;

	if (!capable(CAP_DAC_READ_SEARCH) && !may_decode_fh(&ctx, o_flags)) {
	retval = -EPERM;
	goto out_path;
	}

	if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
	retval = -EFAULT;
	goto out_path;
	}
	if ((f_handle.handle_bytes > MAX_HANDLE_SZ) \|\|
	(f_handle.handle_bytes == 0)) {
	retval = -EINVAL;
	goto out_path;
	}
	handle = kmalloc(struct_size(handle, f_handle, f_handle.handle_bytes),
	GFP_KERNEL);
	if (!handle) {
	retval = -ENOMEM;
	goto out_path;
	}
	/* copy the full handle */
	*handle = f_handle;
	if (copy_from_user(&handle->f_handle,
	&ufh->f_handle,
	f_handle.handle_bytes)) {
	retval = -EFAULT;
	goto out_handle;
	}

	retval = do_handle_to_path(handle, path, &ctx);

	out_handle:
	kfree(handle);
	out_path:
	path_put(&ctx.root);
	out_err:
	return retval;
	}

	static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
	int open_flag)
	{
	long retval = 0;
	struct path path;
	struct file *file;
	int fd;

	retval = handle_to_path(mountdirfd, ufh, &path, open_flag);
	if (retval)
	return retval;

	fd = get_unused_fd_flags(open_flag);
	if (fd < 0) {
	path_put(&path);
	return fd;
	}
	file = file_open_root(&path, "", open_flag, 0);
	if (IS_ERR(file)) {
	put_unused_fd(fd);
	retval = PTR_ERR(file);
	} else {
	retval = fd;
	fd_install(fd, file);
	}
	path_put(&path);
	return retval;
	}

	/**
	* sys_open_by_handle_at: Open the file handle
	* @mountdirfd: directory file descriptor
	* @handle: file handle to be opened
	* @flags: open flags.
	*
	* @mountdirfd indicate the directory file descriptor
	* of the mount point. file handle is decoded relative
	* to the vfsmount pointed by the @mountdirfd. @flags
	* value is same as the open(2) flags.
	*/
	SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
	struct file_handle __user *, handle,
	int, flags)
	{
	long ret;

	if (force_o_largefile())
	flags \|= O_LARGEFILE;

	ret = do_handle_open(mountdirfd, handle, flags);
	return ret;
	}

	#ifdef CONFIG_COMPAT
	/*
	* Exactly like fs/open.c:sys_open_by_handle_at(), except that it
	* doesn't set the O_LARGEFILE flag.
	*/
	COMPAT_SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
	struct file_handle __user *, handle, int, flags)
	{
	return do_handle_open(mountdirfd, handle, flags);
	}
	#endif