fs/crypto/inline_crypt.c - kernel/common.git - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Inline encryption support for fscrypt
  *
  * Copyright 2019 Google LLC
  */

 /*
  * With "inline encryption", the block layer handles the decryption/encryption
  * as part of the bio, instead of the filesystem doing the crypto itself via
  * crypto API.  See Documentation/block/inline-encryption.rst.  fscrypt still
  * provides the key and IV to use.
  */

 #include <linux/blk-crypto.h>
 #include <linux/blkdev.h>
 #include <linux/buffer_head.h>
 #include <linux/keyslot-manager.h>

 #include "fscrypt_private.h"

 /* Return true iff inline encryption should be used for this file */
 bool fscrypt_should_use_inline_encryption(const struct fscrypt_info *ci)
 {
 	const struct inode *inode = ci->ci_inode;
 	struct super_block *sb = inode->i_sb;

 	/* The file must need contents encryption, not filenames encryption */
 	if (!S_ISREG(inode->i_mode))
 		return false;

 	/* blk-crypto must implement the needed encryption algorithm */
 	if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID)
 		return false;

 	/* DIRECT_KEY needs a 24+ byte IV, so it can't work with 8-byte DUNs */
 	if (fscrypt_is_direct_key_policy(&ci->ci_policy))
 		return false;

 	/* The filesystem must be mounted with -o inlinecrypt */
 	if (!sb->s_cop->inline_crypt_enabled ||
 	    !sb->s_cop->inline_crypt_enabled(sb))
 		return false;

 	return true;
 }

 /* Set a per-file inline encryption key (for passing to blk-crypto) */
 int fscrypt_set_inline_crypt_key(struct fscrypt_info *ci, const u8 *derived_key)
 {
 	const struct fscrypt_mode *mode = ci->ci_mode;
 	const struct super_block *sb = ci->ci_inode->i_sb;

 	ci->ci_inline_crypt_key = kmemdup(derived_key, mode->keysize, GFP_NOFS);
 	if (!ci->ci_inline_crypt_key)
 		return -ENOMEM;
 	ci->ci_owns_key = true;

 	return blk_crypto_start_using_mode(mode->blk_crypto_mode,
 					   sb->s_blocksize,
 					   sb->s_bdev->bd_queue);
 }

 /* Free a per-file inline encryption key and evict it from blk-crypto */
 void fscrypt_free_inline_crypt_key(struct fscrypt_info *ci)
 {
 	if (ci->ci_inline_crypt_key != NULL) {
 		const struct fscrypt_mode *mode = ci->ci_mode;
 		const struct super_block *sb = ci->ci_inode->i_sb;

 		blk_crypto_evict_key(sb->s_bdev->bd_queue,
 				     ci->ci_inline_crypt_key,
 				     mode->blk_crypto_mode, sb->s_blocksize);
 		kzfree(ci->ci_inline_crypt_key);
 	}
 }

 /*
  * Set up ->inline_crypt_key (for passing to blk-crypto) for inodes which use an
  * IV_INO_LBLK_64 encryption policy.
  *
  * Return: 0 on success, -errno on failure
  */
 int fscrypt_setup_per_mode_inline_crypt_key(struct fscrypt_info *ci,
 					    struct fscrypt_master_key *mk)
 {
 	static DEFINE_MUTEX(inline_crypt_setup_mutex);
 	const struct super_block *sb = ci->ci_inode->i_sb;
 	struct block_device *bdev = sb->s_bdev;
 	const struct fscrypt_mode *mode = ci->ci_mode;
 	const u8 mode_num = mode - fscrypt_modes;
 	u8 *raw_key;
 	u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
 	int err;

 	if (WARN_ON(mode_num > __FSCRYPT_MODE_MAX))
 		return -EINVAL;

 	/* pairs with smp_store_release() below */
 	raw_key = smp_load_acquire(&mk->mk_iv_ino_lblk_64_raw_keys[mode_num]);
 	if (raw_key) {
 		err = 0;
 		goto out;
 	}

 	mutex_lock(&inline_crypt_setup_mutex);

 	raw_key = mk->mk_iv_ino_lblk_64_raw_keys[mode_num];
 	if (raw_key) {
 		err = 0;
 		goto out_unlock;
 	}

 	raw_key = kmalloc(mode->keysize, GFP_NOFS);
 	if (!raw_key) {
 		err = -ENOMEM;
 		goto out_unlock;
 	}

 	BUILD_BUG_ON(sizeof(mode_num) != 1);
 	BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
 	BUILD_BUG_ON(sizeof(hkdf_info) != 17);
 	hkdf_info[0] = mode_num;
 	memcpy(&hkdf_info[1], &sb->s_uuid, sizeof(sb->s_uuid));

 	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
 				  HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
 				  hkdf_info, sizeof(hkdf_info),
 				  raw_key, mode->keysize);
 	if (err)
 		goto out_unlock;

 	err = blk_crypto_start_using_mode(mode->blk_crypto_mode,
 					  sb->s_blocksize, bdev->bd_queue);
 	if (err)
 		goto out_unlock;

 	/*
 	 * When a master key's first inline encryption key is set up, save a
 	 * reference to the filesystem's block device so that the inline
 	 * encryption keys can be evicted when the master key is destroyed.
 	 */
 	if (!mk->mk_bdev) {
 		mk->mk_bdev = bdgrab(bdev);
 		mk->mk_data_unit_size = sb->s_blocksize;
 	}

 	/* pairs with smp_load_acquire() above */
 	smp_store_release(&mk->mk_iv_ino_lblk_64_raw_keys[mode_num], raw_key);
 	err = 0;
 out_unlock:
 	mutex_unlock(&inline_crypt_setup_mutex);
 out:
 	if (err == 0) {
 		ci->ci_inline_crypt_key = raw_key;
 		/*
 		 * Since each struct fscrypt_master_key belongs to a particular
 		 * filesystem (a struct super_block), there should be only one
 		 * block device, and only one data unit size as it should equal
 		 * the filesystem's blocksize (i.e. s_blocksize).
 		 */
 		if (WARN_ON(mk->mk_bdev != bdev))
 			err = -EINVAL;
 		if (WARN_ON(mk->mk_data_unit_size != sb->s_blocksize))
 			err = -EINVAL;
 	} else {
 		kzfree(raw_key);
 	}
 	return err;
 }

 /*
  * Evict per-mode inline encryption keys from blk-crypto when a master key is
  * destroyed.
  */
 void fscrypt_evict_inline_crypt_keys(struct fscrypt_master_key *mk)
 {
 	struct block_device *bdev = mk->mk_bdev;
 	size_t i;

 	if (!bdev) /* No inline encryption keys? */
 		return;

 	for (i = 0; i < ARRAY_SIZE(mk->mk_iv_ino_lblk_64_raw_keys); i++) {
 		u8 *raw_key = mk->mk_iv_ino_lblk_64_raw_keys[i];

 		if (raw_key != NULL) {
 			blk_crypto_evict_key(bdev->bd_queue, raw_key,
 					     fscrypt_modes[i].blk_crypto_mode,
 					     mk->mk_data_unit_size);
 			kzfree(raw_key);
 		}
 	}
 	bdput(bdev);
 }

 /**
  * fscrypt_inode_uses_inline_crypto - test whether an inode uses inline encryption
  * @inode: an inode
  *
  * Return: true if the inode requires file contents encryption and if the
  *	   encryption should be done in the block layer via blk-crypto rather
  *	   than in the filesystem layer.
  */
 bool fscrypt_inode_uses_inline_crypto(const struct inode *inode)
 {
 	return IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode) &&
 		inode->i_crypt_info->ci_inline_crypt_key != NULL;
 }
 EXPORT_SYMBOL_GPL(fscrypt_inode_uses_inline_crypto);

 /**
  * fscrypt_inode_uses_fs_layer_crypto - test whether an inode uses fs-layer encryption
  * @inode: an inode
  *
  * Return: true if the inode requires file contents encryption and if the
  *	   encryption should be done in the filesystem layer rather than in the
  *	   block layer via blk-crypto.
  */
 bool fscrypt_inode_uses_fs_layer_crypto(const struct inode *inode)
 {
 	return IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode) &&
 		inode->i_crypt_info->ci_inline_crypt_key == NULL;
 }
 EXPORT_SYMBOL_GPL(fscrypt_inode_uses_fs_layer_crypto);

 static inline u64 fscrypt_generate_dun(const struct fscrypt_info *ci,
 				       u64 lblk_num)
 {
 	union fscrypt_iv iv;

 	fscrypt_generate_iv(&iv, lblk_num, ci);
 	/*
 	 * fscrypt_should_use_inline_encryption() ensures we never get here if
 	 * more than the first 8 bytes of the IV are nonzero.
 	 */
 	BUG_ON(memchr_inv(&iv.raw[8], 0, ci->ci_mode->ivsize - 8));
 	return le64_to_cpu(iv.lblk_num);
 }

 /**
  * fscrypt_set_bio_crypt_ctx - prepare a file contents bio for inline encryption
  * @bio: a bio which will eventually be submitted to the file
  * @inode: the file's inode
  * @first_lblk: the first file logical block number in the I/O
  * @gfp_mask: memory allocation flags
  *
  * If the contents of the file should be encrypted (or decrypted) with inline
  * encryption, then assign the appropriate encryption context to the bio.
  *
  * Normally the bio should be newly allocated (i.e. no pages added yet), as
  * otherwise fscrypt_mergeable_bio() won't work as intended.
  *
  * The encryption context will be freed automatically when the bio is freed.
  *
  * Return: 0 on success, -errno on failure.  If __GFP_NOFAIL is specified, this
  *	   is guaranteed to succeed.
  */
 int fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
 			      u64 first_lblk, gfp_t gfp_mask)
 {
 	const struct fscrypt_info *ci = inode->i_crypt_info;
 	u64 dun;

 	if (!fscrypt_inode_uses_inline_crypto(inode))
 		return 0;

 	dun = fscrypt_generate_dun(ci, first_lblk);

 	return bio_crypt_set_ctx(bio, ci->ci_inline_crypt_key,
 				 ci->ci_mode->blk_crypto_mode,
 				 dun, inode->i_blkbits, gfp_mask);
 }
 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx);

 /* Extract the inode and logical block number from a buffer_head. */
 static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh,
 				      const struct inode **inode_ret,
 				      u64 *lblk_num_ret)
 {
 	struct page *page = bh->b_page;
 	const struct address_space *mapping;
 	const struct inode *inode;

 	/*
 	 * The ext4 journal (jbd2) can submit a buffer_head it directly created
 	 * for a non-pagecache page.  fscrypt doesn't care about these.
 	 */
 	mapping = page_mapping(page);
 	if (!mapping)
 		return false;
 	inode = mapping->host;

 	*inode_ret = inode;
 	*lblk_num_ret = ((u64)page->index << (PAGE_SHIFT - inode->i_blkbits)) +
 			(bh_offset(bh) >> inode->i_blkbits);
 	return true;
 }

 /**
  * fscrypt_set_bio_crypt_ctx_bh - prepare a file contents bio for inline encryption
  * @bio: a bio which will eventually be submitted to the file
  * @first_bh: the first buffer_head for which I/O will be submitted
  * @gfp_mask: memory allocation flags
  *
  * Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead
  * of an inode and block number directly.
  *
  * Return: 0 on success, -errno on failure
  */
 int fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
 				 const struct buffer_head *first_bh,
 				 gfp_t gfp_mask)
 {
 	const struct inode *inode;
 	u64 first_lblk;

 	if (!bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk))
 		return 0;

 	return fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask);
 }
 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh);

 /**
  * fscrypt_mergeable_bio - test whether data can be added to a bio
  * @bio: the bio being built up
  * @inode: the inode for the next part of the I/O
  * @next_lblk: the next file logical block number in the I/O
  *
  * When building a bio which may contain data which should undergo inline
  * encryption (or decryption) via fscrypt, filesystems should call this function
  * to ensure that the resulting bio contains only logically contiguous data.
  * This will return false if the next part of the I/O cannot be merged with the
  * bio because either the encryption key would be different or the encryption
  * data unit numbers would be discontiguous.
  *
  * fscrypt_set_bio_crypt_ctx() must have already been called on the bio.
  *
  * Return: true iff the I/O is mergeable
  */
 bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
 			   u64 next_lblk)
 {
 	const struct bio_crypt_ctx *bc;
 	const u8 *next_key;
 	u64 next_dun;

 	if (bio_has_crypt_ctx(bio) != fscrypt_inode_uses_inline_crypto(inode))
 		return false;
 	if (!bio_has_crypt_ctx(bio))
 		return true;
 	bc = bio->bi_crypt_context;
 	next_key = inode->i_crypt_info->ci_inline_crypt_key;
 	next_dun = fscrypt_generate_dun(inode->i_crypt_info, next_lblk);

 	/*
 	 * Comparing the key pointers is good enough, as all I/O for each key
 	 * uses the same pointer.  I.e., there's currently no need to support
 	 * merging requests where the keys are the same but the pointers differ.
 	 */
 	return next_key == bc->raw_key &&
 		next_dun == bc->data_unit_num +
 			    (bio_sectors(bio) >>
 			     (bc->data_unit_size_bits - SECTOR_SHIFT));
 }
 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio);

 /**
  * fscrypt_mergeable_bio_bh - test whether data can be added to a bio
  * @bio: the bio being built up
  * @next_bh: the next buffer_head for which I/O will be submitted
  *
  * Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of
  * an inode and block number directly.
  *
  * Return: true iff the I/O is mergeable
  */
 bool fscrypt_mergeable_bio_bh(struct bio *bio,
 			      const struct buffer_head *next_bh)
 {
 	const struct inode *inode;
 	u64 next_lblk;

 	if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk))
 		return !bio_has_crypt_ctx(bio);

 	return fscrypt_mergeable_bio(bio, inode, next_lblk);
 }
 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Inline encryption support for fscrypt
	*
	* Copyright 2019 Google LLC
	*/

	/*
	* With "inline encryption", the block layer handles the decryption/encryption
	* as part of the bio, instead of the filesystem doing the crypto itself via
	* crypto API. See Documentation/block/inline-encryption.rst. fscrypt still
	* provides the key and IV to use.
	*/

	#include <linux/blk-crypto.h>
	#include <linux/blkdev.h>
	#include <linux/buffer_head.h>
	#include <linux/keyslot-manager.h>

	#include "fscrypt_private.h"

	/* Return true iff inline encryption should be used for this file */
	bool fscrypt_should_use_inline_encryption(const struct fscrypt_info *ci)
	{
	const struct inode *inode = ci->ci_inode;
	struct super_block *sb = inode->i_sb;

	/* The file must need contents encryption, not filenames encryption */
	if (!S_ISREG(inode->i_mode))
	return false;

	/* blk-crypto must implement the needed encryption algorithm */
	if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID)
	return false;

	/* DIRECT_KEY needs a 24+ byte IV, so it can't work with 8-byte DUNs */
	if (fscrypt_is_direct_key_policy(&ci->ci_policy))
	return false;

	/* The filesystem must be mounted with -o inlinecrypt */
	if (!sb->s_cop->inline_crypt_enabled \|\|
	!sb->s_cop->inline_crypt_enabled(sb))
	return false;

	return true;
	}

	/* Set a per-file inline encryption key (for passing to blk-crypto) */
	int fscrypt_set_inline_crypt_key(struct fscrypt_info ci, const u8 derived_key)
	{
	const struct fscrypt_mode *mode = ci->ci_mode;
	const struct super_block *sb = ci->ci_inode->i_sb;

	ci->ci_inline_crypt_key = kmemdup(derived_key, mode->keysize, GFP_NOFS);
	if (!ci->ci_inline_crypt_key)
	return -ENOMEM;
	ci->ci_owns_key = true;

	return blk_crypto_start_using_mode(mode->blk_crypto_mode,
	sb->s_blocksize,
	sb->s_bdev->bd_queue);
	}

	/* Free a per-file inline encryption key and evict it from blk-crypto */
	void fscrypt_free_inline_crypt_key(struct fscrypt_info *ci)
	{
	if (ci->ci_inline_crypt_key != NULL) {
	const struct fscrypt_mode *mode = ci->ci_mode;
	const struct super_block *sb = ci->ci_inode->i_sb;

	blk_crypto_evict_key(sb->s_bdev->bd_queue,
	ci->ci_inline_crypt_key,
	mode->blk_crypto_mode, sb->s_blocksize);
	kzfree(ci->ci_inline_crypt_key);
	}
	}

	/*
	* Set up ->inline_crypt_key (for passing to blk-crypto) for inodes which use an
	* IV_INO_LBLK_64 encryption policy.
	*
	* Return: 0 on success, -errno on failure
	*/
	int fscrypt_setup_per_mode_inline_crypt_key(struct fscrypt_info *ci,
	struct fscrypt_master_key *mk)
	{
	static DEFINE_MUTEX(inline_crypt_setup_mutex);
	const struct super_block *sb = ci->ci_inode->i_sb;
	struct block_device *bdev = sb->s_bdev;
	const struct fscrypt_mode *mode = ci->ci_mode;
	const u8 mode_num = mode - fscrypt_modes;
	u8 *raw_key;
	u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
	int err;

	if (WARN_ON(mode_num > __FSCRYPT_MODE_MAX))
	return -EINVAL;

	/* pairs with smp_store_release() below */
	raw_key = smp_load_acquire(&mk->mk_iv_ino_lblk_64_raw_keys[mode_num]);
	if (raw_key) {
	err = 0;
	goto out;
	}

	mutex_lock(&inline_crypt_setup_mutex);

	raw_key = mk->mk_iv_ino_lblk_64_raw_keys[mode_num];
	if (raw_key) {
	err = 0;
	goto out_unlock;
	}

	raw_key = kmalloc(mode->keysize, GFP_NOFS);
	if (!raw_key) {
	err = -ENOMEM;
	goto out_unlock;
	}

	BUILD_BUG_ON(sizeof(mode_num) != 1);
	BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
	BUILD_BUG_ON(sizeof(hkdf_info) != 17);
	hkdf_info[0] = mode_num;
	memcpy(&hkdf_info[1], &sb->s_uuid, sizeof(sb->s_uuid));

	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
	HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
	hkdf_info, sizeof(hkdf_info),
	raw_key, mode->keysize);
	if (err)
	goto out_unlock;

	err = blk_crypto_start_using_mode(mode->blk_crypto_mode,
	sb->s_blocksize, bdev->bd_queue);
	if (err)
	goto out_unlock;

	/*
	* When a master key's first inline encryption key is set up, save a
	* reference to the filesystem's block device so that the inline
	* encryption keys can be evicted when the master key is destroyed.
	*/
	if (!mk->mk_bdev) {
	mk->mk_bdev = bdgrab(bdev);
	mk->mk_data_unit_size = sb->s_blocksize;
	}

	/* pairs with smp_load_acquire() above */
	smp_store_release(&mk->mk_iv_ino_lblk_64_raw_keys[mode_num], raw_key);
	err = 0;
	out_unlock:
	mutex_unlock(&inline_crypt_setup_mutex);
	out:
	if (err == 0) {
	ci->ci_inline_crypt_key = raw_key;
	/*
	* Since each struct fscrypt_master_key belongs to a particular
	* filesystem (a struct super_block), there should be only one
	* block device, and only one data unit size as it should equal
	* the filesystem's blocksize (i.e. s_blocksize).
	*/
	if (WARN_ON(mk->mk_bdev != bdev))
	err = -EINVAL;
	if (WARN_ON(mk->mk_data_unit_size != sb->s_blocksize))
	err = -EINVAL;
	} else {
	kzfree(raw_key);
	}
	return err;
	}

	/*
	* Evict per-mode inline encryption keys from blk-crypto when a master key is
	* destroyed.
	*/
	void fscrypt_evict_inline_crypt_keys(struct fscrypt_master_key *mk)
	{
	struct block_device *bdev = mk->mk_bdev;
	size_t i;

	if (!bdev) /* No inline encryption keys? */
	return;

	for (i = 0; i < ARRAY_SIZE(mk->mk_iv_ino_lblk_64_raw_keys); i++) {
	u8 *raw_key = mk->mk_iv_ino_lblk_64_raw_keys[i];

	if (raw_key != NULL) {
	blk_crypto_evict_key(bdev->bd_queue, raw_key,
	fscrypt_modes[i].blk_crypto_mode,
	mk->mk_data_unit_size);
	kzfree(raw_key);
	}
	}
	bdput(bdev);
	}

	/**
	* fscrypt_inode_uses_inline_crypto - test whether an inode uses inline encryption
	* @inode: an inode
	*
	* Return: true if the inode requires file contents encryption and if the
	* encryption should be done in the block layer via blk-crypto rather
	* than in the filesystem layer.
	*/
	bool fscrypt_inode_uses_inline_crypto(const struct inode *inode)
	{
	return IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode) &&
	inode->i_crypt_info->ci_inline_crypt_key != NULL;
	}
	EXPORT_SYMBOL_GPL(fscrypt_inode_uses_inline_crypto);

	/**
	* fscrypt_inode_uses_fs_layer_crypto - test whether an inode uses fs-layer encryption
	* @inode: an inode
	*
	* Return: true if the inode requires file contents encryption and if the
	* encryption should be done in the filesystem layer rather than in the
	* block layer via blk-crypto.
	*/
	bool fscrypt_inode_uses_fs_layer_crypto(const struct inode *inode)
	{
	return IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode) &&
	inode->i_crypt_info->ci_inline_crypt_key == NULL;
	}
	EXPORT_SYMBOL_GPL(fscrypt_inode_uses_fs_layer_crypto);

	static inline u64 fscrypt_generate_dun(const struct fscrypt_info *ci,
	u64 lblk_num)
	{
	union fscrypt_iv iv;

	fscrypt_generate_iv(&iv, lblk_num, ci);
	/*
	* fscrypt_should_use_inline_encryption() ensures we never get here if
	* more than the first 8 bytes of the IV are nonzero.
	*/
	BUG_ON(memchr_inv(&iv.raw[8], 0, ci->ci_mode->ivsize - 8));
	return le64_to_cpu(iv.lblk_num);
	}

	/**
	* fscrypt_set_bio_crypt_ctx - prepare a file contents bio for inline encryption
	* @bio: a bio which will eventually be submitted to the file
	* @inode: the file's inode
	* @first_lblk: the first file logical block number in the I/O
	* @gfp_mask: memory allocation flags
	*
	* If the contents of the file should be encrypted (or decrypted) with inline
	* encryption, then assign the appropriate encryption context to the bio.
	*
	* Normally the bio should be newly allocated (i.e. no pages added yet), as
	* otherwise fscrypt_mergeable_bio() won't work as intended.
	*
	* The encryption context will be freed automatically when the bio is freed.
	*
	* Return: 0 on success, -errno on failure. If __GFP_NOFAIL is specified, this
	* is guaranteed to succeed.
	*/
	int fscrypt_set_bio_crypt_ctx(struct bio bio, const struct inode inode,
	u64 first_lblk, gfp_t gfp_mask)
	{
	const struct fscrypt_info *ci = inode->i_crypt_info;
	u64 dun;

	if (!fscrypt_inode_uses_inline_crypto(inode))
	return 0;

	dun = fscrypt_generate_dun(ci, first_lblk);

	return bio_crypt_set_ctx(bio, ci->ci_inline_crypt_key,
	ci->ci_mode->blk_crypto_mode,
	dun, inode->i_blkbits, gfp_mask);
	}
	EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx);

	/* Extract the inode and logical block number from a buffer_head. */
	static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh,
	const struct inode **inode_ret,
	u64 *lblk_num_ret)
	{
	struct page *page = bh->b_page;
	const struct address_space *mapping;
	const struct inode *inode;

	/*
	* The ext4 journal (jbd2) can submit a buffer_head it directly created
	* for a non-pagecache page. fscrypt doesn't care about these.
	*/
	mapping = page_mapping(page);
	if (!mapping)
	return false;
	inode = mapping->host;

	*inode_ret = inode;
	*lblk_num_ret = ((u64)page->index << (PAGE_SHIFT - inode->i_blkbits)) +
	(bh_offset(bh) >> inode->i_blkbits);
	return true;
	}

	/**
	* fscrypt_set_bio_crypt_ctx_bh - prepare a file contents bio for inline encryption
	* @bio: a bio which will eventually be submitted to the file
	* @first_bh: the first buffer_head for which I/O will be submitted
	* @gfp_mask: memory allocation flags
	*
	* Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead
	* of an inode and block number directly.
	*
	* Return: 0 on success, -errno on failure
	*/
	int fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
	const struct buffer_head *first_bh,
	gfp_t gfp_mask)
	{
	const struct inode *inode;
	u64 first_lblk;

	if (!bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk))
	return 0;

	return fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask);
	}
	EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh);

	/**
	* fscrypt_mergeable_bio - test whether data can be added to a bio
	* @bio: the bio being built up
	* @inode: the inode for the next part of the I/O
	* @next_lblk: the next file logical block number in the I/O
	*
	* When building a bio which may contain data which should undergo inline
	* encryption (or decryption) via fscrypt, filesystems should call this function
	* to ensure that the resulting bio contains only logically contiguous data.
	* This will return false if the next part of the I/O cannot be merged with the
	* bio because either the encryption key would be different or the encryption
	* data unit numbers would be discontiguous.
	*
	* fscrypt_set_bio_crypt_ctx() must have already been called on the bio.
	*
	* Return: true iff the I/O is mergeable
	*/
	bool fscrypt_mergeable_bio(struct bio bio, const struct inode inode,
	u64 next_lblk)
	{
	const struct bio_crypt_ctx *bc;
	const u8 *next_key;
	u64 next_dun;

	if (bio_has_crypt_ctx(bio) != fscrypt_inode_uses_inline_crypto(inode))
	return false;
	if (!bio_has_crypt_ctx(bio))
	return true;
	bc = bio->bi_crypt_context;
	next_key = inode->i_crypt_info->ci_inline_crypt_key;
	next_dun = fscrypt_generate_dun(inode->i_crypt_info, next_lblk);

	/*
	* Comparing the key pointers is good enough, as all I/O for each key
	* uses the same pointer. I.e., there's currently no need to support
	* merging requests where the keys are the same but the pointers differ.
	*/
	return next_key == bc->raw_key &&
	next_dun == bc->data_unit_num +
	(bio_sectors(bio) >>
	(bc->data_unit_size_bits - SECTOR_SHIFT));
	}
	EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio);

	/**
	* fscrypt_mergeable_bio_bh - test whether data can be added to a bio
	* @bio: the bio being built up
	* @next_bh: the next buffer_head for which I/O will be submitted
	*
	* Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of
	* an inode and block number directly.
	*
	* Return: true iff the I/O is mergeable
	*/
	bool fscrypt_mergeable_bio_bh(struct bio *bio,
	const struct buffer_head *next_bh)
	{
	const struct inode *inode;
	u64 next_lblk;

	if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk))
	return !bio_has_crypt_ctx(bio);

	return fscrypt_mergeable_bio(bio, inode, next_lblk);
	}
	EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);