text: // SPDX-License-Identifier: GPL-2.0-or-later
  /*
   * symlink.c - operations for configfs symlinks.
   *
   * Based on sysfs:
   * 	sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
   *
   * configfs Copyright (C) 2005 Oracle.  All rights reserved.
   */
  
  #include <linux/fs.h>
  #include <linux/module.h>
  #include <linux/namei.h>
  #include <linux/slab.h>
  
  #include <linux/configfs.h>
  #include "configfs_internal.h"
  
  /* Protects attachments of new symlinks */
  DEFINE_MUTEX(configfs_symlink_mutex);
  
  static int item_depth(struct config_item * item)
  {
  	struct config_item * p = item;
  	int depth = 0;
  	do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
  	return depth;
  }
  
  static int item_path_length(struct config_item * item)
  {
  	struct config_item * p = item;
  	int length = 1;
  	do {
  		length += strlen(config_item_name(p)) + 1;
  		p = p->ci_parent;
  	} while (p && !configfs_is_root(p));
  	return length;
  }
  
  static void fill_item_path(struct config_item * item, char * buffer, int length)
  {
  	struct config_item * p;
  
  	--length;
  	for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
  		int cur = strlen(config_item_name(p));
  
  		/* back up enough to print this bus id with '/' */
  		length -= cur;
  		memcpy(buffer + length, config_item_name(p), cur);
  		*(buffer + --length) = '/';
  	}
  }
  
  static int configfs_get_target_path(struct config_item *item,
  		struct config_item *target, char *path)
  {
  	int depth, size;
  	char *s;
  
  	depth = item_depth(item);
  	size = item_path_length(target) + depth * 3 - 1;
  	if (size > PATH_MAX)
  		return -ENAMETOOLONG;
  
  	pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
  
  	for (s = path; depth--; s += 3)
  		strcpy(s,"../");
  
  	fill_item_path(target, path, size);
  	pr_debug("%s: path = '%s'\n", __func__, path);
  	return 0;
  }
  
  static int create_link(struct config_item *parent_item,
  		       struct config_item *item,
  		       struct dentry *dentry)
  {
  	struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
  	char *body;
  	int ret;
  
  	if (!configfs_dirent_is_ready(target_sd))
  		return -ENOENT;
  
  	body = kzalloc(PAGE_SIZE, GFP_KERNEL);
  	if (!body)
  		return -ENOMEM;
  
  	configfs_get(target_sd);
  	spin_lock(&configfs_dirent_lock);
  	if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
  		spin_unlock(&configfs_dirent_lock);
  		configfs_put(target_sd);
  		kfree(body);
  		return -ENOENT;
  	}
  	target_sd->s_links++;
  	spin_unlock(&configfs_dirent_lock);
  	ret = configfs_get_target_path(parent_item, item, body);
  	if (!ret)
  		ret = configfs_create_link(target_sd, parent_item->ci_dentry,
  					   dentry, body);
  	if (ret) {
  		spin_lock(&configfs_dirent_lock);
  		target_sd->s_links--;
  		spin_unlock(&configfs_dirent_lock);
  		configfs_put(target_sd);
  		kfree(body);
  	}
  	return ret;
  }
  
  
  static int get_target(const char *symname, struct path *path,
  		      struct config_item **target, struct super_block *sb)
  {
  	int ret;
  
  	ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
  	if (!ret) {
  		if (path->dentry->d_sb == sb) {
  			*target = configfs_get_config_item(path->dentry);
  			if (!*target) {
  				ret = -ENOENT;
  				path_put(path);
  			}
  		} else {
  			ret = -EPERM;
  			path_put(path);
  		}
  	}
  
  	return ret;
  }
  
  
  int configfs_symlink(struct user_namespace *mnt_userns, struct inode *dir,
  		     struct dentry *dentry, const char *symname)
  {
  	int ret;
  	struct path path;
  	struct configfs_dirent *sd;
  	struct config_item *parent_item;
  	struct config_item *target_item = NULL;
  	const struct config_item_type *type;
  
  	sd = dentry->d_parent->d_fsdata;
  	/*
  	 * Fake invisibility if dir belongs to a group/default groups hierarchy
  	 * being attached
  	 */
  	if (!configfs_dirent_is_ready(sd))
  		return -ENOENT;
  
  	parent_item = configfs_get_config_item(dentry->d_parent);
  	type = parent_item->ci_type;
  
  	ret = -EPERM;
  	if (!type || !type->ct_item_ops ||
  	    !type->ct_item_ops->allow_link)
  		goto out_put;
  
  	/*
  	 * This is really sick.  What they wanted was a hybrid of
  	 * link(2) and symlink(2) - they wanted the target resolved
  	 * at syscall time (as link(2) would've done), be a directory
  	 * (which link(2) would've refused to do) *AND* be a deep
  	 * fucking magic, making the target busy from rmdir POV.
  	 * symlink(2) is nothing of that sort, and the locking it
  	 * gets matches the normal symlink(2) semantics.  Without
  	 * attempts to resolve the target (which might very well
  	 * not even exist yet) done prior to locking the parent
  	 * directory.  This perversion, OTOH, needs to resolve
  	 * the target, which would lead to obvious deadlocks if
  	 * attempted with any directories locked.
  	 *
  	 * Unfortunately, that garbage is userland ABI and we should've
  	 * said "no" back in 2005.  Too late now, so we get to
  	 * play very ugly games with locking.
  	 *
  	 * Try *ANYTHING* of that sort in new code, and you will
  	 * really regret it.  Just ask yourself - what could a BOFH
  	 * do to me and do I want to find it out first-hand?
  	 *
  	 *  AV, a thoroughly annoyed bastard.
  	 */
  	inode_unlock(dir);
  	ret = get_target(symname, &path, &target_item, dentry->d_sb);
  	inode_lock(dir);
  	if (ret)
  		goto out_put;
  
  	if (dentry->d_inode || d_unhashed(dentry))
  		ret = -EEXIST;
  	else
  		ret = inode_permission(&init_user_ns, dir,
  				       MAY_WRITE | MAY_EXEC);
  	if (!ret)
  		ret = type->ct_item_ops->allow_link(parent_item, target_item);
  	if (!ret) {
  		mutex_lock(&configfs_symlink_mutex);
  		ret = create_link(parent_item, target_item, dentry);
  		mutex_unlock(&configfs_symlink_mutex);
  		if (ret && type->ct_item_ops->drop_link)
  			type->ct_item_ops->drop_link(parent_item,
  						     target_item);
  	}
  
  	config_item_put(target_item);
  	path_put(&path);
  
  out_put:
  	config_item_put(parent_item);
  	return ret;
  }
  
  int configfs_unlink(struct inode *dir, struct dentry *dentry)
  {
  	struct configfs_dirent *sd = dentry->d_fsdata, *target_sd;
  	struct config_item *parent_item;
  	const struct config_item_type *type;
  	int ret;
  
  	ret = -EPERM;  /* What lack-of-symlink returns */
  	if (!(sd->s_type & CONFIGFS_ITEM_LINK))
  		goto out;
  
  	target_sd = sd->s_element;
  
  	parent_item = configfs_get_config_item(dentry->d_parent);
  	type = parent_item->ci_type;
  
  	spin_lock(&configfs_dirent_lock);
  	list_del_init(&sd->s_sibling);
  	spin_unlock(&configfs_dirent_lock);
  	configfs_drop_dentry(sd, dentry->d_parent);
  	dput(dentry);
  	configfs_put(sd);
  
  	/*
  	 * drop_link() must be called before
  	 * decrementing target's ->s_links, so that the order of
  	 * drop_link(this, target) and drop_item(target) is preserved.
  	 */
  	if (type && type->ct_item_ops &&
  	    type->ct_item_ops->drop_link)
  		type->ct_item_ops->drop_link(parent_item,
  					       target_sd->s_element);
  
  	spin_lock(&configfs_dirent_lock);
  	target_sd->s_links--;
  	spin_unlock(&configfs_dirent_lock);
  	configfs_put(target_sd);
  
  	config_item_put(parent_item);
  
  	ret = 0;
  
  out:
  	return ret;
  }
  
  const struct inode_operations configfs_symlink_inode_operations = {
  	.get_link = simple_get_link,
  	.setattr = configfs_setattr,
  };
  
  