1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Utility functions for file contents encryption/decryption on
4 * block device-based filesystems.
5 *
6 * Copyright (C) 2015, Google, Inc.
7 * Copyright (C) 2015, Motorola Mobility
8 */
9
10#include <linux/pagemap.h>
11#include <linux/module.h>
12#include <linux/bio.h>
13#include <linux/namei.h>
14#include "fscrypt_private.h"
15
16/**
17 * fscrypt_decrypt_bio() - decrypt the contents of a bio
18 * @bio: the bio to decrypt
19 *
20 * Decrypt the contents of a "read" bio following successful completion of the
21 * underlying disk read.  The bio must be reading a whole number of blocks of an
22 * encrypted file directly into the page cache.  If the bio is reading the
23 * ciphertext into bounce pages instead of the page cache (for example, because
24 * the file is also compressed, so decompression is required after decryption),
25 * then this function isn't applicable.  This function may sleep, so it must be
26 * called from a workqueue rather than from the bio's bi_end_io callback.
27 *
28 * Return: %true on success; %false on failure.  On failure, bio->bi_status is
29 *	   also set to an error status.
30 */
31bool fscrypt_decrypt_bio(struct bio *bio)
32{
33	struct folio_iter fi;
34
35	bio_for_each_folio_all(fi, bio) {
36		int err = fscrypt_decrypt_pagecache_blocks(fi.folio, fi.length,
37							   fi.offset);
38
39		if (err) {
40			bio->bi_status = errno_to_blk_status(err);
41			return false;
42		}
43	}
44	return true;
45}
46EXPORT_SYMBOL(fscrypt_decrypt_bio);
47
48static int fscrypt_zeroout_range_inline_crypt(const struct inode *inode,
49					      pgoff_t lblk, sector_t pblk,
50					      unsigned int len)
51{
52	const unsigned int blockbits = inode->i_blkbits;
53	const unsigned int blocks_per_page = 1 << (PAGE_SHIFT - blockbits);
54	struct bio *bio;
55	int ret, err = 0;
56	int num_pages = 0;
57
58	/* This always succeeds since __GFP_DIRECT_RECLAIM is set. */
59	bio = bio_alloc(inode->i_sb->s_bdev, BIO_MAX_VECS, REQ_OP_WRITE,
60			GFP_NOFS);
61
62	while (len) {
63		unsigned int blocks_this_page = min(len, blocks_per_page);
64		unsigned int bytes_this_page = blocks_this_page << blockbits;
65
66		if (num_pages == 0) {
67			fscrypt_set_bio_crypt_ctx(bio, inode, lblk, GFP_NOFS);
68			bio->bi_iter.bi_sector =
69					pblk << (blockbits - SECTOR_SHIFT);
70		}
71		ret = bio_add_page(bio, ZERO_PAGE(0), bytes_this_page, 0);
72		if (WARN_ON_ONCE(ret != bytes_this_page)) {
73			err = -EIO;
74			goto out;
75		}
76		num_pages++;
77		len -= blocks_this_page;
78		lblk += blocks_this_page;
79		pblk += blocks_this_page;
80		if (num_pages == BIO_MAX_VECS || !len ||
81		    !fscrypt_mergeable_bio(bio, inode, lblk)) {
82			err = submit_bio_wait(bio);
83			if (err)
84				goto out;
85			bio_reset(bio, inode->i_sb->s_bdev, REQ_OP_WRITE);
86			num_pages = 0;
87		}
88	}
89out:
90	bio_put(bio);
91	return err;
92}
93
94/**
95 * fscrypt_zeroout_range() - zero out a range of blocks in an encrypted file
96 * @inode: the file's inode
97 * @lblk: the first file logical block to zero out
98 * @pblk: the first filesystem physical block to zero out
99 * @len: number of blocks to zero out
100 *
101 * Zero out filesystem blocks in an encrypted regular file on-disk, i.e. write
102 * ciphertext blocks which decrypt to the all-zeroes block.  The blocks must be
103 * both logically and physically contiguous.  It's also assumed that the
104 * filesystem only uses a single block device, ->s_bdev.
105 *
106 * Note that since each block uses a different IV, this involves writing a
107 * different ciphertext to each block; we can't simply reuse the same one.
108 *
109 * Return: 0 on success; -errno on failure.
110 */
111int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,
112			  sector_t pblk, unsigned int len)
113{
114	const struct fscrypt_inode_info *ci = inode->i_crypt_info;
115	const unsigned int du_bits = ci->ci_data_unit_bits;
116	const unsigned int du_size = 1U << du_bits;
117	const unsigned int du_per_page_bits = PAGE_SHIFT - du_bits;
118	const unsigned int du_per_page = 1U << du_per_page_bits;
119	u64 du_index = (u64)lblk << (inode->i_blkbits - du_bits);
120	u64 du_remaining = (u64)len << (inode->i_blkbits - du_bits);
121	sector_t sector = pblk << (inode->i_blkbits - SECTOR_SHIFT);
122	struct page *pages[16]; /* write up to 16 pages at a time */
123	unsigned int nr_pages;
124	unsigned int i;
125	unsigned int offset;
126	struct bio *bio;
127	int ret, err;
128
129	if (len == 0)
130		return 0;
131
132	if (fscrypt_inode_uses_inline_crypto(inode))
133		return fscrypt_zeroout_range_inline_crypt(inode, lblk, pblk,
134							  len);
135
136	BUILD_BUG_ON(ARRAY_SIZE(pages) > BIO_MAX_VECS);
137	nr_pages = min_t(u64, ARRAY_SIZE(pages),
138			 (du_remaining + du_per_page - 1) >> du_per_page_bits);
139
140	/*
141	 * We need at least one page for ciphertext.  Allocate the first one
142	 * from a mempool, with __GFP_DIRECT_RECLAIM set so that it can't fail.
143	 *
144	 * Any additional page allocations are allowed to fail, as they only
145	 * help performance, and waiting on the mempool for them could deadlock.
146	 */
147	for (i = 0; i < nr_pages; i++) {
148		pages[i] = fscrypt_alloc_bounce_page(i == 0 ? GFP_NOFS :
149						     GFP_NOWAIT | __GFP_NOWARN);
150		if (!pages[i])
151			break;
152	}
153	nr_pages = i;
154	if (WARN_ON_ONCE(nr_pages <= 0))
155		return -EINVAL;
156
157	/* This always succeeds since __GFP_DIRECT_RECLAIM is set. */
158	bio = bio_alloc(inode->i_sb->s_bdev, nr_pages, REQ_OP_WRITE, GFP_NOFS);
159
160	do {
161		bio->bi_iter.bi_sector = sector;
162
163		i = 0;
164		offset = 0;
165		do {
166			err = fscrypt_crypt_data_unit(ci, FS_ENCRYPT, du_index,
167						      ZERO_PAGE(0), pages[i],
168						      du_size, offset,
169						      GFP_NOFS);
170			if (err)
171				goto out;
172			du_index++;
173			sector += 1U << (du_bits - SECTOR_SHIFT);
174			du_remaining--;
175			offset += du_size;
176			if (offset == PAGE_SIZE || du_remaining == 0) {
177				ret = bio_add_page(bio, pages[i++], offset, 0);
178				if (WARN_ON_ONCE(ret != offset)) {
179					err = -EIO;
180					goto out;
181				}
182				offset = 0;
183			}
184		} while (i != nr_pages && du_remaining != 0);
185
186		err = submit_bio_wait(bio);
187		if (err)
188			goto out;
189		bio_reset(bio, inode->i_sb->s_bdev, REQ_OP_WRITE);
190	} while (du_remaining != 0);
191	err = 0;
192out:
193	bio_put(bio);
194	for (i = 0; i < nr_pages; i++)
195		fscrypt_free_bounce_page(pages[i]);
196	return err;
197}
198EXPORT_SYMBOL(fscrypt_zeroout_range);
199