inline_crypt.c

// 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/sched/mm.h>
#include <linux/slab.h>

#include "fscrypt_private.h"

struct fscrypt_blk_crypto_key {
	struct blk_crypto_key base;
	int num_devs;
	struct request_queue *devs[];
};

static int fscrypt_get_num_devices(struct super_block *sb)
{
	if (sb->s_cop->get_num_devices)
		return sb->s_cop->get_num_devices(sb);
	return 1;
}

static void fscrypt_get_devices(struct super_block *sb, int num_devs,
				struct request_queue **devs)
{
	if (num_devs == 1)
		devs[0] = bdev_get_queue(sb->s_bdev);
	else
		sb->s_cop->get_devices(sb, devs);
}

static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_info *ci)
{
	struct super_block *sb = ci->ci_inode->i_sb;
	unsigned int flags = fscrypt_policy_flags(&ci->ci_policy);
	int ino_bits = 64, lblk_bits = 64;

	if (flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
		return offsetofend(union fscrypt_iv, nonce);

	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64)
		return sizeof(__le64);

	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)
		return sizeof(__le32);

	/* Default case: IVs are just the file logical block number */
	if (sb->s_cop->get_ino_and_lblk_bits)
		sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
	return DIV_ROUND_UP(lblk_bits, 8);
}

/* Enable inline encryption for this file if supported. */
int fscrypt_select_encryption_impl(struct fscrypt_info *ci)
{
	const struct inode *inode = ci->ci_inode;
	struct super_block *sb = inode->i_sb;
	struct blk_crypto_config crypto_cfg;
	int num_devs;
	struct request_queue **devs;
	int i;

	/* The file must need contents encryption, not filenames encryption */
	if (!fscrypt_needs_contents_encryption(inode))
		return 0;

	/* The crypto mode must have a blk-crypto counterpart */
	if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID)
		return 0;

	/* The filesystem must be mounted with -o inlinecrypt */
	if (!(sb->s_flags & SB_INLINECRYPT))
		return 0;

	/*
	 * When a page contains multiple logically contiguous filesystem blocks,
	 * some filesystem code only calls fscrypt_mergeable_bio() for the first
	 * block in the page. This is fine for most of fscrypt's IV generation
	 * strategies, where contiguous blocks imply contiguous IVs. But it
	 * doesn't work with IV_INO_LBLK_32. For now, simply exclude
	 * IV_INO_LBLK_32 with blocksize != PAGE_SIZE from inline encryption.
	 */
	if ((fscrypt_policy_flags(&ci->ci_policy) &
	     FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) &&
	    sb->s_blocksize != PAGE_SIZE)
		return 0;

	/*
	 * On all the filesystem's devices, blk-crypto must support the crypto
	 * configuration that the file would use.
	 */
	crypto_cfg.crypto_mode = ci->ci_mode->blk_crypto_mode;
	crypto_cfg.data_unit_size = sb->s_blocksize;
	crypto_cfg.dun_bytes = fscrypt_get_dun_bytes(ci);
	num_devs = fscrypt_get_num_devices(sb);
	devs = kmalloc_array(num_devs, sizeof(*devs), GFP_NOFS);
	if (!devs)
		return -ENOMEM;
	fscrypt_get_devices(sb, num_devs, devs);

	for (i = 0; i < num_devs; i++) {
		if (!blk_crypto_config_supported(devs[i], &crypto_cfg))
			goto out_free_devs;
	}

	ci->ci_inlinecrypt = true;
out_free_devs:
	kfree(devs);

	return 0;
}

int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
				     const u8 *raw_key,
				     const struct fscrypt_info *ci)
{
	const struct inode *inode = ci->ci_inode;
	struct super_block *sb = inode->i_sb;
	enum blk_crypto_mode_num crypto_mode = ci->ci_mode->blk_crypto_mode;
	int num_devs = fscrypt_get_num_devices(sb);
	int queue_refs = 0;
	struct fscrypt_blk_crypto_key *blk_key;
	int err;
	int i;
	unsigned int flags;

	blk_key = kzalloc(struct_size(blk_key, devs, num_devs), GFP_NOFS);
	if (!blk_key)
		return -ENOMEM;

	blk_key->num_devs = num_devs;
	fscrypt_get_devices(sb, num_devs, blk_key->devs);

	err = blk_crypto_init_key(&blk_key->base, raw_key, crypto_mode,
				  fscrypt_get_dun_bytes(ci), sb->s_blocksize);
	if (err) {
		fscrypt_err(inode, "error %d initializing blk-crypto key", err);
		goto fail;
	}

	/*
	 * We have to start using blk-crypto on all the filesystem's devices.
	 * We also have to save all the request_queue's for later so that the
	 * key can be evicted from them.  This is needed because some keys
	 * aren't destroyed until after the filesystem was already unmounted
	 * (namely, the per-mode keys in struct fscrypt_master_key).
	 */
	for (i = 0; i < num_devs; i++) {
		if (!blk_get_queue(blk_key->devs[i])) {
			fscrypt_err(inode, "couldn't get request_queue");
			err = -EAGAIN;
			goto fail;
		}
		queue_refs++;

		flags = memalloc_nofs_save();
		err = blk_crypto_start_using_key(&blk_key->base,
						 blk_key->devs[i]);
		memalloc_nofs_restore(flags);
		if (err) {
			fscrypt_err(inode,
				    "error %d starting to use blk-crypto", err);
			goto fail;
		}
	}
	/*
	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
	 * I.e., here we publish ->blk_key with a RELEASE barrier so that
	 * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
	 * possible for per-mode keys, not for per-file keys.
	 */
	smp_store_release(&prep_key->blk_key, blk_key);
	return 0;

fail:
	for (i = 0; i < queue_refs; i++)
		blk_put_queue(blk_key->devs[i]);
	kfree_sensitive(blk_key);
	return err;
}

void fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key)
{
	struct fscrypt_blk_crypto_key *blk_key = prep_key->blk_key;
	int i;

	if (blk_key) {
		for (i = 0; i < blk_key->num_devs; i++) {
			blk_crypto_evict_key(blk_key->devs[i], &blk_key->base);
			blk_put_queue(blk_key->devs[i]);
		}
		kfree_sensitive(blk_key);
	}
}

bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
{
	return inode->i_crypt_info->ci_inlinecrypt;
}
EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto);

static void fscrypt_generate_dun(const struct fscrypt_info *ci, u64 lblk_num,
				 u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE])
{
	union fscrypt_iv iv;
	int i;

	fscrypt_generate_iv(&iv, lblk_num, ci);

	BUILD_BUG_ON(FSCRYPT_MAX_IV_SIZE > BLK_CRYPTO_MAX_IV_SIZE);
	memset(dun, 0, BLK_CRYPTO_MAX_IV_SIZE);
	for (i = 0; i < ci->ci_mode->ivsize/sizeof(dun[0]); i++)
		dun[i] = le64_to_cpu(iv.dun[i]);
}

/**
 * fscrypt_set_bio_crypt_ctx() - prepare a file contents bio for inline crypto
 * @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 - these must be a waiting mask so that
 *					bio_crypt_set_ctx can't fail.
 *
 * 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.
 */
void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
			       u64 first_lblk, gfp_t gfp_mask)
{
	const struct fscrypt_info *ci;
	u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];

	if (!fscrypt_inode_uses_inline_crypto(inode))
		return;
	ci = inode->i_crypt_info;

	fscrypt_generate_dun(ci, first_lblk, dun);
	bio_crypt_set_ctx(bio, &ci->ci_enc_key.blk_key->base, dun, 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
 *				    crypto
 * @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.
 */
void 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))
		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 contiguous data unit numbers.
 * 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 = bio->bi_crypt_context;
	u64 next_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];

	if (!!bc != fscrypt_inode_uses_inline_crypto(inode))
		return false;
	if (!bc)
		return true;

	/*
	 * 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.
	 */
	if (bc->bc_key != &inode->i_crypt_info->ci_enc_key.blk_key->base)
		return false;

	fscrypt_generate_dun(inode->i_crypt_info, next_lblk, next_dun);
	return bio_crypt_dun_is_contiguous(bc, bio->bi_iter.bi_size, next_dun);
}
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->bi_crypt_context;

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