/*
    File: fs/xattr.c
  
    Extended attribute handling.
  
    Copyright (C) 2001 by Andreas Gruenbacher <a.gruenbacher@computer.org>
    Copyright (C) 2001 SGI - Silicon Graphics, Inc <linux-xfs@oss.sgi.com>
    Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
   */
  #include <linux/fs.h>
  #include <linux/slab.h>

  #include <linux/file.h>
  #include <linux/xattr.h>

  #include <linux/mount.h>

  #include <linux/namei.h>
  #include <linux/security.h>

  #include <linux/evm.h>

  #include <linux/syscalls.h>

  #include <linux/export.h>

  #include <linux/fsnotify.h>

  #include <linux/audit.h>

  #include <linux/vmalloc.h>

  #include <linux/posix_acl_xattr.h>

  #include <linux/uaccess.h>

  #include "internal.h"

  static const char *
  strcmp_prefix(const char *a, const char *a_prefix)
  {
  	while (*a_prefix && *a == *a_prefix) {
  		a++;
  		a_prefix++;
  	}
  	return *a_prefix ? NULL : a;
  }
  
  /*
   * In order to implement different sets of xattr operations for each xattr

   * prefix, a filesystem should create a null-terminated array of struct
   * xattr_handler (one for each prefix) and hang a pointer to it off of the
   * s_xattr field of the superblock.

   */
  #define for_each_xattr_handler(handlers, handler)		\
  	if (handlers)						\
  		for ((handler) = *(handlers)++;			\
  			(handler) != NULL;			\
  			(handler) = *(handlers)++)
  
  /*
   * Find the xattr_handler with the matching prefix.
   */
  static const struct xattr_handler *

  xattr_resolve_name(struct inode *inode, const char **name)

  {

  	const struct xattr_handler **handlers = inode->i_sb->s_xattr;

  	const struct xattr_handler *handler;

  	if (!(inode->i_opflags & IOP_XATTR)) {
  		if (unlikely(is_bad_inode(inode)))
  			return ERR_PTR(-EIO);

  		return ERR_PTR(-EOPNOTSUPP);

  	}

  	for_each_xattr_handler(handlers, handler) {
  		const char *n;
  
  		n = strcmp_prefix(*name, xattr_prefix(handler));
  		if (n) {
  			if (!handler->prefix ^ !*n) {
  				if (*n)
  					continue;
  				return ERR_PTR(-EINVAL);
  			}
  			*name = n;
  			return handler;
  		}
  	}
  	return ERR_PTR(-EOPNOTSUPP);
  }

  /*
   * Check permissions for extended attribute access.  This is a bit complicated
   * because different namespaces have very different rules.
   */
  static int
  xattr_permission(struct inode *inode, const char *name, int mask)
  {
  	/*
  	 * We can never set or remove an extended attribute on a read-only
  	 * filesystem  or on an immutable / append-only inode.
  	 */
  	if (mask & MAY_WRITE) {

  		if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
  			return -EPERM;

  		/*
  		 * Updating an xattr will likely cause i_uid and i_gid
  		 * to be writen back improperly if their true value is
  		 * unknown to the vfs.
  		 */
  		if (HAS_UNMAPPED_ID(inode))
  			return -EPERM;

  	}
  
  	/*
  	 * No restriction for security.* and system.* from the VFS.  Decision
  	 * on these is left to the underlying filesystem / security module.
  	 */
  	if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) ||
  	    !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
  		return 0;
  
  	/*

  	 * The trusted.* namespace can only be accessed by privileged users.

  	 */

  	if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN)) {
  		if (!capable(CAP_SYS_ADMIN))
  			return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
  		return 0;
  	}

  	/*
  	 * In the user.* namespace, only regular files and directories can have

  	 * extended attributes. For sticky directories, only the owner and

  	 * privileged users can write attributes.

  	 */

  	if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {

  		if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))

  			return (mask & MAY_WRITE) ? -EPERM : -ENODATA;

  		if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&

  		    (mask & MAY_WRITE) && !inode_owner_or_capable(inode))

  			return -EPERM;
  	}

  	return inode_permission(inode, mask);

  }

  int
  __vfs_setxattr(struct dentry *dentry, struct inode *inode, const char *name,
  	       const void *value, size_t size, int flags)
  {

  	const struct xattr_handler *handler;
  
  	handler = xattr_resolve_name(inode, &name);
  	if (IS_ERR(handler))
  		return PTR_ERR(handler);
  	if (!handler->set)

  		return -EOPNOTSUPP;

  	if (size == 0)
  		value = "";  /* empty EA, do not remove */
  	return handler->set(handler, dentry, inode, name, value, size, flags);

  }
  EXPORT_SYMBOL(__vfs_setxattr);

  /**
   *  __vfs_setxattr_noperm - perform setxattr operation without performing
   *  permission checks.
   *
   *  @dentry - object to perform setxattr on
   *  @name - xattr name to set
   *  @value - value to set @name to
   *  @size - size of @value
   *  @flags - flags to pass into filesystem operations
   *
   *  returns the result of the internal setxattr or setsecurity operations.
   *
   *  This function requires the caller to lock the inode's i_mutex before it
   *  is executed. It also assumes that the caller will make the appropriate
   *  permission checks.
   */
  int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
  		const void *value, size_t size, int flags)

  {
  	struct inode *inode = dentry->d_inode;

  	int error = -EAGAIN;

  	int issec = !strncmp(name, XATTR_SECURITY_PREFIX,
  				   XATTR_SECURITY_PREFIX_LEN);

  	if (issec)
  		inode->i_flags &= ~S_NOSEC;

  	if (inode->i_opflags & IOP_XATTR) {

  		error = __vfs_setxattr(dentry, inode, name, value, size, flags);

  		if (!error) {
  			fsnotify_xattr(dentry);
  			security_inode_post_setxattr(dentry, name, value,
  						     size, flags);
  		}

  	} else {

  		if (unlikely(is_bad_inode(inode)))
  			return -EIO;

  	}
  	if (error == -EAGAIN) {
  		error = -EOPNOTSUPP;
  
  		if (issec) {
  			const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
  
  			error = security_inode_setsecurity(inode, suffix, value,
  							   size, flags);
  			if (!error)
  				fsnotify_xattr(dentry);
  		}

  	}

  
  	return error;
  }
  
  
  int
  vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
  		size_t size, int flags)
  {
  	struct inode *inode = dentry->d_inode;
  	int error;
  
  	error = xattr_permission(inode, name, MAY_WRITE);
  	if (error)
  		return error;

  	inode_lock(inode);

  	error = security_inode_setxattr(dentry, name, value, size, flags);
  	if (error)
  		goto out;
  
  	error = __vfs_setxattr_noperm(dentry, name, value, size, flags);

  out:

  	inode_unlock(inode);

  	return error;
  }
  EXPORT_SYMBOL_GPL(vfs_setxattr);
  
  ssize_t

  xattr_getsecurity(struct inode *inode, const char *name, void *value,
  			size_t size)
  {
  	void *buffer = NULL;
  	ssize_t len;
  
  	if (!value || !size) {
  		len = security_inode_getsecurity(inode, name, &buffer, false);
  		goto out_noalloc;
  	}
  
  	len = security_inode_getsecurity(inode, name, &buffer, true);
  	if (len < 0)
  		return len;
  	if (size < len) {
  		len = -ERANGE;
  		goto out;
  	}
  	memcpy(value, buffer, len);
  out:

  	kfree(buffer);

  out_noalloc:
  	return len;
  }
  EXPORT_SYMBOL_GPL(xattr_getsecurity);

  /*
   * vfs_getxattr_alloc - allocate memory, if necessary, before calling getxattr
   *
   * Allocate memory, if not already allocated, or re-allocate correct size,
   * before retrieving the extended attribute.
   *
   * Returns the result of alloc, if failed, or the getxattr operation.
   */
  ssize_t
  vfs_getxattr_alloc(struct dentry *dentry, const char *name, char **xattr_value,
  		   size_t xattr_size, gfp_t flags)
  {

  	const struct xattr_handler *handler;

  	struct inode *inode = dentry->d_inode;
  	char *value = *xattr_value;
  	int error;
  
  	error = xattr_permission(inode, name, MAY_READ);
  	if (error)
  		return error;

  	handler = xattr_resolve_name(inode, &name);
  	if (IS_ERR(handler))
  		return PTR_ERR(handler);
  	if (!handler->get)

  		return -EOPNOTSUPP;

  	error = handler->get(handler, dentry, inode, name, NULL, 0);

  	if (error < 0)
  		return error;
  
  	if (!value || (error > xattr_size)) {
  		value = krealloc(*xattr_value, error + 1, flags);
  		if (!value)
  			return -ENOMEM;
  		memset(value, 0, error + 1);
  	}

  	error = handler->get(handler, dentry, inode, name, value, error);

  	*xattr_value = value;
  	return error;
  }

  ssize_t

  __vfs_getxattr(struct dentry *dentry, struct inode *inode, const char *name,
  	       void *value, size_t size)
  {

  	const struct xattr_handler *handler;
  
  	handler = xattr_resolve_name(inode, &name);
  	if (IS_ERR(handler))
  		return PTR_ERR(handler);
  	if (!handler->get)

  		return -EOPNOTSUPP;

  	return handler->get(handler, dentry, inode, name, value, size);

  }
  EXPORT_SYMBOL(__vfs_getxattr);
  
  ssize_t

  vfs_getxattr(struct dentry *dentry, const char *name, void *value, size_t size)

  {
  	struct inode *inode = dentry->d_inode;
  	int error;

  	error = xattr_permission(inode, name, MAY_READ);
  	if (error)
  		return error;

  	error = security_inode_getxattr(dentry, name);
  	if (error)
  		return error;

  	if (!strncmp(name, XATTR_SECURITY_PREFIX,

  				XATTR_SECURITY_PREFIX_LEN)) {
  		const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;

  		int ret = xattr_getsecurity(inode, suffix, value, size);

  		/*
  		 * Only overwrite the return value if a security module
  		 * is actually active.
  		 */

  		if (ret == -EOPNOTSUPP)
  			goto nolsm;
  		return ret;

  	}

  nolsm:

  	return __vfs_getxattr(dentry, inode, name, value, size);

  }
  EXPORT_SYMBOL_GPL(vfs_getxattr);

  ssize_t

  vfs_listxattr(struct dentry *dentry, char *list, size_t size)

  {

  	struct inode *inode = d_inode(dentry);

  	ssize_t error;

  	error = security_inode_listxattr(dentry);

  	if (error)
  		return error;

  	if (inode->i_op->listxattr && (inode->i_opflags & IOP_XATTR)) {
  		error = -EOPNOTSUPP;
  		error = inode->i_op->listxattr(dentry, list, size);

  	} else {

  		error = security_inode_listsecurity(inode, list, size);

  		if (size && error > size)
  			error = -ERANGE;
  	}
  	return error;
  }
  EXPORT_SYMBOL_GPL(vfs_listxattr);

  int

  __vfs_removexattr(struct dentry *dentry, const char *name)

  {

  	struct inode *inode = d_inode(dentry);
  	const struct xattr_handler *handler;

  	handler = xattr_resolve_name(inode, &name);
  	if (IS_ERR(handler))
  		return PTR_ERR(handler);
  	if (!handler->set)

  		return -EOPNOTSUPP;

  	return handler->set(handler, dentry, inode, name, NULL, 0, XATTR_REPLACE);

  }
  EXPORT_SYMBOL(__vfs_removexattr);
  
  int
  vfs_removexattr(struct dentry *dentry, const char *name)
  {
  	struct inode *inode = dentry->d_inode;
  	int error;

  	error = xattr_permission(inode, name, MAY_WRITE);
  	if (error)
  		return error;

  	inode_lock(inode);

  	error = security_inode_removexattr(dentry, name);

  	if (error)
  		goto out;

  	error = __vfs_removexattr(dentry, name);

  	if (!error) {

  		fsnotify_xattr(dentry);

  		evm_inode_post_removexattr(dentry, name);
  	}

  
  out:

  	inode_unlock(inode);

  	return error;
  }
  EXPORT_SYMBOL_GPL(vfs_removexattr);

  /*
   * Extended attribute SET operations
   */
  static long

  setxattr(struct dentry *d, const char __user *name, const void __user *value,

  	 size_t size, int flags)
  {
  	int error;
  	void *kvalue = NULL;
  	char kname[XATTR_NAME_MAX + 1];
  
  	if (flags & ~(XATTR_CREATE|XATTR_REPLACE))
  		return -EINVAL;
  
  	error = strncpy_from_user(kname, name, sizeof(kname));
  	if (error == 0 || error == sizeof(kname))
  		error = -ERANGE;
  	if (error < 0)
  		return error;
  
  	if (size) {
  		if (size > XATTR_SIZE_MAX)
  			return -E2BIG;

  		kvalue = kvmalloc(size, GFP_KERNEL);
  		if (!kvalue)
  			return -ENOMEM;

  		if (copy_from_user(kvalue, value, size)) {
  			error = -EFAULT;
  			goto out;
  		}

  		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
  		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
  			posix_acl_fix_xattr_from_user(kvalue, size);

  		else if (strcmp(kname, XATTR_NAME_CAPS) == 0) {
  			error = cap_convert_nscap(d, &kvalue, size);
  			if (error < 0)
  				goto out;
  			size = error;
  		}

  	}

  	error = vfs_setxattr(d, kname, kvalue, size, flags);

  out:

  	kvfree(kvalue);

  	return error;
  }

  static int path_setxattr(const char __user *pathname,
  			 const char __user *name, const void __user *value,
  			 size_t size, int flags, unsigned int lookup_flags)

  {

  	struct path path;

  	int error;

  retry:
  	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);

  	if (error)
  		return error;

  	error = mnt_want_write(path.mnt);

  	if (!error) {

  		error = setxattr(path.dentry, name, value, size, flags);
  		mnt_drop_write(path.mnt);

  	}

  	path_put(&path);

  	if (retry_estale(error, lookup_flags)) {
  		lookup_flags |= LOOKUP_REVAL;
  		goto retry;
  	}

  	return error;
  }

  SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
  		const char __user *, name, const void __user *, value,
  		size_t, size, int, flags)
  {
  	return path_setxattr(pathname, name, value, size, flags, LOOKUP_FOLLOW);
  }

  SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
  		const char __user *, name, const void __user *, value,
  		size_t, size, int, flags)

  {

  	return path_setxattr(pathname, name, value, size, flags, 0);

  }

  SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
  		const void __user *,value, size_t, size, int, flags)

  {

  	struct fd f = fdget(fd);

  	int error = -EBADF;

  	if (!f.file)

  		return error;

  	audit_file(f.file);

  	error = mnt_want_write_file_path(f.file);

  	if (!error) {

  		error = setxattr(f.file->f_path.dentry, name, value, size, flags);

  		mnt_drop_write_file_path(f.file);

  	}

  	fdput(f);

  	return error;
  }
  
  /*
   * Extended attribute GET operations
   */
  static ssize_t

  getxattr(struct dentry *d, const char __user *name, void __user *value,
  	 size_t size)

  {
  	ssize_t error;
  	void *kvalue = NULL;
  	char kname[XATTR_NAME_MAX + 1];
  
  	error = strncpy_from_user(kname, name, sizeof(kname));
  	if (error == 0 || error == sizeof(kname))
  		error = -ERANGE;
  	if (error < 0)
  		return error;
  
  	if (size) {
  		if (size > XATTR_SIZE_MAX)
  			size = XATTR_SIZE_MAX;

  		kvalue = kvzalloc(size, GFP_KERNEL);
  		if (!kvalue)
  			return -ENOMEM;

  	}

  	error = vfs_getxattr(d, kname, kvalue, size);

  	if (error > 0) {

  		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
  		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))

  			posix_acl_fix_xattr_to_user(kvalue, error);

  		if (size && copy_to_user(value, kvalue, error))
  			error = -EFAULT;
  	} else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
  		/* The file system tried to returned a value bigger
  		   than XATTR_SIZE_MAX bytes. Not possible. */
  		error = -E2BIG;

  	}

  
  	kvfree(kvalue);

  	return error;
  }

  static ssize_t path_getxattr(const char __user *pathname,
  			     const char __user *name, void __user *value,
  			     size_t size, unsigned int lookup_flags)

  {

  	struct path path;

  	ssize_t error;

  retry:
  	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);

  	if (error)
  		return error;

  	error = getxattr(path.dentry, name, value, size);
  	path_put(&path);

  	if (retry_estale(error, lookup_flags)) {
  		lookup_flags |= LOOKUP_REVAL;
  		goto retry;
  	}

  	return error;
  }

  SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
  		const char __user *, name, void __user *, value, size_t, size)
  {
  	return path_getxattr(pathname, name, value, size, LOOKUP_FOLLOW);
  }

  SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
  		const char __user *, name, void __user *, value, size_t, size)

  {

  	return path_getxattr(pathname, name, value, size, 0);

  }

  SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
  		void __user *, value, size_t, size)

  {

  	struct fd f = fdget(fd);

  	ssize_t error = -EBADF;

  	if (!f.file)

  		return error;

  	audit_file(f.file);

  	error = getxattr(f.file->f_path.dentry, name, value, size);
  	fdput(f);

  	return error;
  }
  
  /*
   * Extended attribute LIST operations
   */
  static ssize_t
  listxattr(struct dentry *d, char __user *list, size_t size)
  {
  	ssize_t error;
  	char *klist = NULL;
  
  	if (size) {
  		if (size > XATTR_LIST_MAX)
  			size = XATTR_LIST_MAX;

  		klist = kvmalloc(size, GFP_KERNEL);
  		if (!klist)
  			return -ENOMEM;

  	}

  	error = vfs_listxattr(d, klist, size);

  	if (error > 0) {
  		if (size && copy_to_user(list, klist, error))
  			error = -EFAULT;
  	} else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
  		/* The file system tried to returned a list bigger
  		   than XATTR_LIST_MAX bytes. Not possible. */
  		error = -E2BIG;

  	}

  
  	kvfree(klist);

  	return error;
  }

  static ssize_t path_listxattr(const char __user *pathname, char __user *list,
  			      size_t size, unsigned int lookup_flags)

  {

  	struct path path;

  	ssize_t error;

  retry:
  	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);

  	if (error)
  		return error;

  	error = listxattr(path.dentry, list, size);
  	path_put(&path);

  	if (retry_estale(error, lookup_flags)) {
  		lookup_flags |= LOOKUP_REVAL;
  		goto retry;
  	}

  	return error;
  }

  SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
  		size_t, size)
  {
  	return path_listxattr(pathname, list, size, LOOKUP_FOLLOW);
  }

  SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
  		size_t, size)

  {

  	return path_listxattr(pathname, list, size, 0);

  }

  SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)

  {

  	struct fd f = fdget(fd);

  	ssize_t error = -EBADF;

  	if (!f.file)

  		return error;

  	audit_file(f.file);

  	error = listxattr(f.file->f_path.dentry, list, size);
  	fdput(f);

  	return error;
  }
  
  /*
   * Extended attribute REMOVE operations
   */
  static long

  removexattr(struct dentry *d, const char __user *name)

  {
  	int error;
  	char kname[XATTR_NAME_MAX + 1];
  
  	error = strncpy_from_user(kname, name, sizeof(kname));
  	if (error == 0 || error == sizeof(kname))
  		error = -ERANGE;
  	if (error < 0)
  		return error;

  	return vfs_removexattr(d, kname);

  }

  static int path_removexattr(const char __user *pathname,
  			    const char __user *name, unsigned int lookup_flags)

  {

  	struct path path;

  	int error;

  retry:
  	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);

  	if (error)
  		return error;

  	error = mnt_want_write(path.mnt);

  	if (!error) {

  		error = removexattr(path.dentry, name);
  		mnt_drop_write(path.mnt);

  	}

  	path_put(&path);

  	if (retry_estale(error, lookup_flags)) {
  		lookup_flags |= LOOKUP_REVAL;
  		goto retry;
  	}

  	return error;
  }

  SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
  		const char __user *, name)
  {
  	return path_removexattr(pathname, name, LOOKUP_FOLLOW);
  }

  SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
  		const char __user *, name)

  {

  	return path_removexattr(pathname, name, 0);

  }

  SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)

  {

  	struct fd f = fdget(fd);

  	int error = -EBADF;

  	if (!f.file)

  		return error;

  	audit_file(f.file);

  	error = mnt_want_write_file_path(f.file);

  	if (!error) {

  		error = removexattr(f.file->f_path.dentry, name);

  		mnt_drop_write_file_path(f.file);

  	}

  	fdput(f);

  	return error;
  }

  /*

   * Combine the results of the list() operation from every xattr_handler in the
   * list.
   */
  ssize_t
  generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
  {

  	const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;

  	unsigned int size = 0;
  
  	if (!buffer) {

  		for_each_xattr_handler(handlers, handler) {

  			if (!handler->name ||
  			    (handler->list && !handler->list(dentry)))

  				continue;

  			size += strlen(handler->name) + 1;

  		}

  	} else {
  		char *buf = buffer;

  		size_t len;

  
  		for_each_xattr_handler(handlers, handler) {

  			if (!handler->name ||
  			    (handler->list && !handler->list(dentry)))

  				continue;

  			len = strlen(handler->name);
  			if (len + 1 > buffer_size)

  				return -ERANGE;

  			memcpy(buf, handler->name, len + 1);
  			buf += len + 1;
  			buffer_size -= len + 1;

  		}
  		size = buf - buffer;
  	}
  	return size;
  }

  EXPORT_SYMBOL(generic_listxattr);

  /**
   * xattr_full_name  -  Compute full attribute name from suffix
   *
   * @handler:	handler of the xattr_handler operation
   * @name:	name passed to the xattr_handler operation
   *
   * The get and set xattr handler operations are called with the remainder of
   * the attribute name after skipping the handler's prefix: for example, "foo"
   * is passed to the get operation of a handler with prefix "user." to get
   * attribute "user.foo".  The full name is still "there" in the name though.
   *
   * Note: the list xattr handler operation when called from the vfs is passed a
   * NULL name; some file systems use this operation internally, with varying
   * semantics.
   */
  const char *xattr_full_name(const struct xattr_handler *handler,
  			    const char *name)
  {

  	size_t prefix_len = strlen(xattr_prefix(handler));

  
  	return name - prefix_len;
  }
  EXPORT_SYMBOL(xattr_full_name);

  /*
   * Allocate new xattr and copy in the value; but leave the name to callers.
   */
  struct simple_xattr *simple_xattr_alloc(const void *value, size_t size)
  {
  	struct simple_xattr *new_xattr;
  	size_t len;
  
  	/* wrap around? */
  	len = sizeof(*new_xattr) + size;

  	if (len < sizeof(*new_xattr))

  		return NULL;
  
  	new_xattr = kmalloc(len, GFP_KERNEL);
  	if (!new_xattr)
  		return NULL;
  
  	new_xattr->size = size;
  	memcpy(new_xattr->value, value, size);
  	return new_xattr;
  }
  
  /*
   * xattr GET operation for in-memory/pseudo filesystems
   */
  int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
  		     void *buffer, size_t size)
  {
  	struct simple_xattr *xattr;
  	int ret = -ENODATA;
  
  	spin_lock(&xattrs->lock);
  	list_for_each_entry(xattr, &xattrs->head, list) {
  		if (strcmp(name, xattr->name))
  			continue;
  
  		ret = xattr->size;
  		if (buffer) {
  			if (size < xattr->size)
  				ret = -ERANGE;
  			else
  				memcpy(buffer, xattr->value, xattr->size);
  		}
  		break;
  	}
  	spin_unlock(&xattrs->lock);
  	return ret;
  }

  /**
   * simple_xattr_set - xattr SET operation for in-memory/pseudo filesystems
   * @xattrs: target simple_xattr list
   * @name: name of the extended attribute
   * @value: value of the xattr. If %NULL, will remove the attribute.
   * @size: size of the new xattr
   * @flags: %XATTR_{CREATE|REPLACE}
   *
   * %XATTR_CREATE is set, the xattr shouldn't exist already; otherwise fails
   * with -EEXIST.  If %XATTR_REPLACE is set, the xattr should exist;
   * otherwise, fails with -ENODATA.
   *
   * Returns 0 on success, -errno on failure.
   */
  int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
  		     const void *value, size_t size, int flags)

  {
  	struct simple_xattr *xattr;

  	struct simple_xattr *new_xattr = NULL;

  	int err = 0;
  
  	/* value == NULL means remove */
  	if (value) {
  		new_xattr = simple_xattr_alloc(value, size);
  		if (!new_xattr)
  			return -ENOMEM;
  
  		new_xattr->name = kstrdup(name, GFP_KERNEL);
  		if (!new_xattr->name) {
  			kfree(new_xattr);
  			return -ENOMEM;
  		}
  	}
  
  	spin_lock(&xattrs->lock);
  	list_for_each_entry(xattr, &xattrs->head, list) {
  		if (!strcmp(name, xattr->name)) {
  			if (flags & XATTR_CREATE) {
  				xattr = new_xattr;
  				err = -EEXIST;
  			} else if (new_xattr) {
  				list_replace(&xattr->list, &new_xattr->list);
  			} else {
  				list_del(&xattr->list);
  			}
  			goto out;
  		}
  	}
  	if (flags & XATTR_REPLACE) {
  		xattr = new_xattr;
  		err = -ENODATA;
  	} else {
  		list_add(&new_xattr->list, &xattrs->head);
  		xattr = NULL;
  	}
  out:
  	spin_unlock(&xattrs->lock);
  	if (xattr) {
  		kfree(xattr->name);
  		kfree(xattr);
  	}
  	return err;
  
  }

  static bool xattr_is_trusted(const char *name)
  {
  	return !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN);
  }

  static int xattr_list_one(char **buffer, ssize_t *remaining_size,
  			  const char *name)
  {
  	size_t len = strlen(name) + 1;
  	if (*buffer) {
  		if (*remaining_size < len)
  			return -ERANGE;
  		memcpy(*buffer, name, len);
  		*buffer += len;
  	}
  	*remaining_size -= len;
  	return 0;
  }

  /*
   * xattr LIST operation for in-memory/pseudo filesystems
   */

  ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs,
  			  char *buffer, size_t size)

  {
  	bool trusted = capable(CAP_SYS_ADMIN);
  	struct simple_xattr *xattr;

  	ssize_t remaining_size = size;

  	int err = 0;

  
  #ifdef CONFIG_FS_POSIX_ACL

  	if (IS_POSIXACL(inode)) {
  		if (inode->i_acl) {
  			err = xattr_list_one(&buffer, &remaining_size,
  					     XATTR_NAME_POSIX_ACL_ACCESS);
  			if (err)
  				return err;
  		}
  		if (inode->i_default_acl) {
  			err = xattr_list_one(&buffer, &remaining_size,
  					     XATTR_NAME_POSIX_ACL_DEFAULT);
  			if (err)
  				return err;
  		}

  	}
  #endif

  
  	spin_lock(&xattrs->lock);
  	list_for_each_entry(xattr, &xattrs->head, list) {

  		/* skip "trusted." attributes for unprivileged callers */
  		if (!trusted && xattr_is_trusted(xattr->name))
  			continue;

  		err = xattr_list_one(&buffer, &remaining_size, xattr->name);
  		if (err)

  			break;

  	}
  	spin_unlock(&xattrs->lock);

  	return err ? err : size - remaining_size;

  }

  /*
   * Adds an extended attribute to the list
   */

  void simple_xattr_list_add(struct simple_xattrs *xattrs,
  			   struct simple_xattr *new_xattr)
  {
  	spin_lock(&xattrs->lock);
  	list_add(&new_xattr->list, &xattrs->head);
  	spin_unlock(&xattrs->lock);
  }