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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  */
fscrypt_decrypt_bio(struct bio * bio)31 bool fscrypt_decrypt_bio(struct bio *bio)
32 {
33 	struct bio_vec *bv;
34 	struct bvec_iter_all iter_all;
35 
36 	bio_for_each_segment_all(bv, bio, iter_all) {
37 		struct page *page = bv->bv_page;
38 		int err = fscrypt_decrypt_pagecache_blocks(page, bv->bv_len,
39 							   bv->bv_offset);
40 
41 		if (err) {
42 			bio->bi_status = errno_to_blk_status(err);
43 			return false;
44 		}
45 	}
46 	return true;
47 }
48 EXPORT_SYMBOL(fscrypt_decrypt_bio);
49 
fscrypt_zeroout_range_inline_crypt(const struct inode * inode,pgoff_t lblk,sector_t pblk,unsigned int len)50 static int fscrypt_zeroout_range_inline_crypt(const struct inode *inode,
51 					      pgoff_t lblk, sector_t pblk,
52 					      unsigned int len)
53 {
54 	const unsigned int blockbits = inode->i_blkbits;
55 	const unsigned int blocks_per_page = 1 << (PAGE_SHIFT - blockbits);
56 	struct bio *bio;
57 	int ret, err = 0;
58 	int num_pages = 0;
59 
60 	/* This always succeeds since __GFP_DIRECT_RECLAIM is set. */
61 	bio = bio_alloc(GFP_NOFS, BIO_MAX_VECS);
62 
63 	while (len) {
64 		unsigned int blocks_this_page = min(len, blocks_per_page);
65 		unsigned int bytes_this_page = blocks_this_page << blockbits;
66 
67 		if (num_pages == 0) {
68 			fscrypt_set_bio_crypt_ctx(bio, inode, lblk, GFP_NOFS);
69 			bio_set_dev(bio, inode->i_sb->s_bdev);
70 			bio->bi_iter.bi_sector =
71 					pblk << (blockbits - SECTOR_SHIFT);
72 			bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
73 		}
74 		ret = bio_add_page(bio, ZERO_PAGE(0), bytes_this_page, 0);
75 		if (WARN_ON_ONCE(ret != bytes_this_page)) {
76 			err = -EIO;
77 			goto out;
78 		}
79 		num_pages++;
80 		len -= blocks_this_page;
81 		lblk += blocks_this_page;
82 		pblk += blocks_this_page;
83 		if (num_pages == BIO_MAX_VECS || !len ||
84 		    !fscrypt_mergeable_bio(bio, inode, lblk)) {
85 			err = submit_bio_wait(bio);
86 			if (err)
87 				goto out;
88 			bio_reset(bio);
89 			num_pages = 0;
90 		}
91 	}
92 out:
93 	bio_put(bio);
94 	return err;
95 }
96 
97 /**
98  * fscrypt_zeroout_range() - zero out a range of blocks in an encrypted file
99  * @inode: the file's inode
100  * @lblk: the first file logical block to zero out
101  * @pblk: the first filesystem physical block to zero out
102  * @len: number of blocks to zero out
103  *
104  * Zero out filesystem blocks in an encrypted regular file on-disk, i.e. write
105  * ciphertext blocks which decrypt to the all-zeroes block.  The blocks must be
106  * both logically and physically contiguous.  It's also assumed that the
107  * filesystem only uses a single block device, ->s_bdev.
108  *
109  * Note that since each block uses a different IV, this involves writing a
110  * different ciphertext to each block; we can't simply reuse the same one.
111  *
112  * Return: 0 on success; -errno on failure.
113  */
fscrypt_zeroout_range(const struct inode * inode,pgoff_t lblk,sector_t pblk,unsigned int len)114 int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,
115 			  sector_t pblk, unsigned int len)
116 {
117 	const struct fscrypt_info *ci = inode->i_crypt_info;
118 	const unsigned int du_bits = ci->ci_data_unit_bits;
119 	const unsigned int du_size = 1U << du_bits;
120 	const unsigned int du_per_page_bits = PAGE_SHIFT - du_bits;
121 	const unsigned int du_per_page = 1U << du_per_page_bits;
122 	u64 du_index = (u64)lblk << (inode->i_blkbits - du_bits);
123 	u64 du_remaining = (u64)len << (inode->i_blkbits - du_bits);
124 	sector_t sector = pblk << (inode->i_blkbits - SECTOR_SHIFT);
125 	struct page *pages[16]; /* write up to 16 pages at a time */
126 	unsigned int nr_pages;
127 	unsigned int i;
128 	unsigned int offset;
129 	struct bio *bio;
130 	int ret, err;
131 
132 	if (len == 0)
133 		return 0;
134 
135 	if (fscrypt_inode_uses_inline_crypto(inode))
136 		return fscrypt_zeroout_range_inline_crypt(inode, lblk, pblk,
137 							  len);
138 
139 	BUILD_BUG_ON(ARRAY_SIZE(pages) > BIO_MAX_VECS);
140 	nr_pages = min_t(u64, ARRAY_SIZE(pages),
141 			 (du_remaining + du_per_page - 1) >> du_per_page_bits);
142 
143 	/*
144 	 * We need at least one page for ciphertext.  Allocate the first one
145 	 * from a mempool, with __GFP_DIRECT_RECLAIM set so that it can't fail.
146 	 *
147 	 * Any additional page allocations are allowed to fail, as they only
148 	 * help performance, and waiting on the mempool for them could deadlock.
149 	 */
150 	for (i = 0; i < nr_pages; i++) {
151 		pages[i] = fscrypt_alloc_bounce_page(i == 0 ? GFP_NOFS :
152 						     GFP_NOWAIT | __GFP_NOWARN);
153 		if (!pages[i])
154 			break;
155 	}
156 	nr_pages = i;
157 	if (WARN_ON_ONCE(nr_pages <= 0))
158 		return -EINVAL;
159 
160 	/* This always succeeds since __GFP_DIRECT_RECLAIM is set. */
161 	bio = bio_alloc(GFP_NOFS, nr_pages);
162 
163 	do {
164 		bio_set_dev(bio, inode->i_sb->s_bdev);
165 		bio->bi_iter.bi_sector = sector;
166 		bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
167 
168 		i = 0;
169 		offset = 0;
170 		do {
171 			err = fscrypt_crypt_data_unit(ci, FS_ENCRYPT, du_index,
172 						      ZERO_PAGE(0), pages[i],
173 						      du_size, offset,
174 						      GFP_NOFS);
175 			if (err)
176 				goto out;
177 			du_index++;
178 			sector += 1U << (du_bits - SECTOR_SHIFT);
179 			du_remaining--;
180 			offset += du_size;
181 			if (offset == PAGE_SIZE || du_remaining == 0) {
182 				ret = bio_add_page(bio, pages[i++], offset, 0);
183 				if (WARN_ON_ONCE(ret != offset)) {
184 					err = -EIO;
185 					goto out;
186 				}
187 				offset = 0;
188 			}
189 		} while (i != nr_pages && du_remaining != 0);
190 
191 		err = submit_bio_wait(bio);
192 		if (err)
193 			goto out;
194 		bio_reset(bio);
195 	} while (du_remaining != 0);
196 	err = 0;
197 out:
198 	bio_put(bio);
199 	for (i = 0; i < nr_pages; i++)
200 		fscrypt_free_bounce_page(pages[i]);
201 	return err;
202 }
203 EXPORT_SYMBOL(fscrypt_zeroout_range);
204