/*
   * Encryption policy functions for per-file encryption support.
   *
   * Copyright (C) 2015, Google, Inc.
   * Copyright (C) 2015, Motorola Mobility.
   *
   * Written by Michael Halcrow, 2015.
   * Modified by Jaegeuk Kim, 2015.
   */
  
  #include <linux/random.h>
  #include <linux/string.h>
  #include <linux/fscrypto.h>

  #include <linux/mount.h>

  
  static int inode_has_encryption_context(struct inode *inode)
  {
  	if (!inode->i_sb->s_cop->get_context)
  		return 0;
  	return (inode->i_sb->s_cop->get_context(inode, NULL, 0L) > 0);
  }
  
  /*
   * check whether the policy is consistent with the encryption context
   * for the inode
   */
  static int is_encryption_context_consistent_with_policy(struct inode *inode,
  				const struct fscrypt_policy *policy)
  {
  	struct fscrypt_context ctx;
  	int res;
  
  	if (!inode->i_sb->s_cop->get_context)
  		return 0;
  
  	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
  	if (res != sizeof(ctx))
  		return 0;
  
  	return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
  			FS_KEY_DESCRIPTOR_SIZE) == 0 &&
  			(ctx.flags == policy->flags) &&
  			(ctx.contents_encryption_mode ==
  			 policy->contents_encryption_mode) &&
  			(ctx.filenames_encryption_mode ==
  			 policy->filenames_encryption_mode));
  }
  
  static int create_encryption_context_from_policy(struct inode *inode,
  				const struct fscrypt_policy *policy)
  {
  	struct fscrypt_context ctx;
  	int res;
  
  	if (!inode->i_sb->s_cop->set_context)
  		return -EOPNOTSUPP;
  
  	if (inode->i_sb->s_cop->prepare_context) {
  		res = inode->i_sb->s_cop->prepare_context(inode);
  		if (res)
  			return res;
  	}
  
  	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
  	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
  					FS_KEY_DESCRIPTOR_SIZE);
  
  	if (!fscrypt_valid_contents_enc_mode(
  				policy->contents_encryption_mode)) {
  		printk(KERN_WARNING
  		       "%s: Invalid contents encryption mode %d
  ", __func__,
  			policy->contents_encryption_mode);
  		return -EINVAL;
  	}
  
  	if (!fscrypt_valid_filenames_enc_mode(
  				policy->filenames_encryption_mode)) {
  		printk(KERN_WARNING
  			"%s: Invalid filenames encryption mode %d
  ", __func__,
  			policy->filenames_encryption_mode);
  		return -EINVAL;
  	}
  
  	if (policy->flags & ~FS_POLICY_FLAGS_VALID)
  		return -EINVAL;
  
  	ctx.contents_encryption_mode = policy->contents_encryption_mode;
  	ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
  	ctx.flags = policy->flags;
  	BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
  	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
  
  	return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
  }

  int fscrypt_process_policy(struct file *filp,

  				const struct fscrypt_policy *policy)
  {

  	struct inode *inode = file_inode(filp);
  	int ret;

  	if (!inode_owner_or_capable(inode))
  		return -EACCES;

  	if (policy->version != 0)
  		return -EINVAL;

  	ret = mnt_want_write_file(filp);
  	if (ret)
  		return ret;

  	inode_lock(inode);

  	if (!inode_has_encryption_context(inode)) {

  		if (!S_ISDIR(inode->i_mode))

  			ret = -EINVAL;
  		else if (!inode->i_sb->s_cop->empty_dir)
  			ret = -EOPNOTSUPP;
  		else if (!inode->i_sb->s_cop->empty_dir(inode))
  			ret = -ENOTEMPTY;
  		else
  			ret = create_encryption_context_from_policy(inode,
  								    policy);
  	} else if (!is_encryption_context_consistent_with_policy(inode,
  								 policy)) {
  		printk(KERN_WARNING
  		       "%s: Policy inconsistent with encryption context
  ",
  		       __func__);
  		ret = -EINVAL;

  	}

  	inode_unlock(inode);

  	mnt_drop_write_file(filp);
  	return ret;

  }
  EXPORT_SYMBOL(fscrypt_process_policy);
  
  int fscrypt_get_policy(struct inode *inode, struct fscrypt_policy *policy)
  {
  	struct fscrypt_context ctx;
  	int res;
  
  	if (!inode->i_sb->s_cop->get_context ||
  			!inode->i_sb->s_cop->is_encrypted(inode))
  		return -ENODATA;
  
  	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
  	if (res != sizeof(ctx))
  		return -ENODATA;
  	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
  		return -EINVAL;
  
  	policy->version = 0;
  	policy->contents_encryption_mode = ctx.contents_encryption_mode;
  	policy->filenames_encryption_mode = ctx.filenames_encryption_mode;
  	policy->flags = ctx.flags;
  	memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
  				FS_KEY_DESCRIPTOR_SIZE);
  	return 0;
  }
  EXPORT_SYMBOL(fscrypt_get_policy);
  
  int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
  {
  	struct fscrypt_info *parent_ci, *child_ci;
  	int res;
  
  	if ((parent == NULL) || (child == NULL)) {
  		printk(KERN_ERR	"parent %p child %p
  ", parent, child);
  		BUG_ON(1);
  	}

  	/* No restrictions on file types which are never encrypted */
  	if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
  	    !S_ISLNK(child->i_mode))
  		return 1;

  	/* no restrictions if the parent directory is not encrypted */
  	if (!parent->i_sb->s_cop->is_encrypted(parent))
  		return 1;
  	/* if the child directory is not encrypted, this is always a problem */
  	if (!parent->i_sb->s_cop->is_encrypted(child))
  		return 0;
  	res = fscrypt_get_encryption_info(parent);
  	if (res)
  		return 0;
  	res = fscrypt_get_encryption_info(child);
  	if (res)
  		return 0;
  	parent_ci = parent->i_crypt_info;
  	child_ci = child->i_crypt_info;
  	if (!parent_ci && !child_ci)
  		return 1;
  	if (!parent_ci || !child_ci)
  		return 0;
  
  	return (memcmp(parent_ci->ci_master_key,
  			child_ci->ci_master_key,
  			FS_KEY_DESCRIPTOR_SIZE) == 0 &&
  		(parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
  		(parent_ci->ci_filename_mode == child_ci->ci_filename_mode) &&
  		(parent_ci->ci_flags == child_ci->ci_flags));
  }
  EXPORT_SYMBOL(fscrypt_has_permitted_context);
  
  /**
   * fscrypt_inherit_context() - Sets a child context from its parent
   * @parent: Parent inode from which the context is inherited.
   * @child:  Child inode that inherits the context from @parent.
   * @fs_data:  private data given by FS.
   * @preload:  preload child i_crypt_info
   *
   * Return: Zero on success, non-zero otherwise
   */
  int fscrypt_inherit_context(struct inode *parent, struct inode *child,
  						void *fs_data, bool preload)
  {
  	struct fscrypt_context ctx;
  	struct fscrypt_info *ci;
  	int res;
  
  	if (!parent->i_sb->s_cop->set_context)
  		return -EOPNOTSUPP;
  
  	res = fscrypt_get_encryption_info(parent);
  	if (res < 0)
  		return res;
  
  	ci = parent->i_crypt_info;
  	if (ci == NULL)
  		return -ENOKEY;
  
  	ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
  	if (fscrypt_dummy_context_enabled(parent)) {
  		ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
  		ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
  		ctx.flags = 0;
  		memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
  		res = 0;
  	} else {
  		ctx.contents_encryption_mode = ci->ci_data_mode;
  		ctx.filenames_encryption_mode = ci->ci_filename_mode;
  		ctx.flags = ci->ci_flags;
  		memcpy(ctx.master_key_descriptor, ci->ci_master_key,
  				FS_KEY_DESCRIPTOR_SIZE);
  	}
  	get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
  	res = parent->i_sb->s_cop->set_context(child, &ctx,
  						sizeof(ctx), fs_data);
  	if (res)
  		return res;
  	return preload ? fscrypt_get_encryption_info(child): 0;
  }
  EXPORT_SYMBOL(fscrypt_inherit_context);