1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * fs/ext4/verity.c: fs-verity support for ext4
  4 *
  5 * Copyright 2019 Google LLC
  6 */
  7
  8/*
  9 * Implementation of fsverity_operations for ext4.
 10 *
 11 * ext4 stores the verity metadata (Merkle tree and fsverity_descriptor) past
 12 * the end of the file, starting at the first 64K boundary beyond i_size.  This
 13 * approach works because (a) verity files are readonly, and (b) pages fully
 14 * beyond i_size aren't visible to userspace but can be read/written internally
 15 * by ext4 with only some relatively small changes to ext4.  This approach
 16 * avoids having to depend on the EA_INODE feature and on rearchitecturing
 17 * ext4's xattr support to support paging multi-gigabyte xattrs into memory, and
 18 * to support encrypting xattrs.  Note that the verity metadata *must* be
 19 * encrypted when the file is, since it contains hashes of the plaintext data.
 20 *
 21 * Using a 64K boundary rather than a 4K one keeps things ready for
 22 * architectures with 64K pages, and it doesn't necessarily waste space on-disk
 23 * since there can be a hole between i_size and the start of the Merkle tree.
 24 */
 25
 26#include <linux/quotaops.h>
 27
 28#include "ext4.h"
 29#include "ext4_extents.h"
 30#include "ext4_jbd2.h"
 31
 32static inline loff_t ext4_verity_metadata_pos(const struct inode *inode)
 33{
 34	return round_up(inode->i_size, 65536);
 35}
 36
 37/*
 38 * Read some verity metadata from the inode.  __vfs_read() can't be used because
 39 * we need to read beyond i_size.
 40 */
 41static int pagecache_read(struct inode *inode, void *buf, size_t count,
 42			  loff_t pos)
 43{
 44	while (count) {
 45		size_t n = min_t(size_t, count,
 46				 PAGE_SIZE - offset_in_page(pos));
 47		struct page *page;
 48		void *addr;
 49
 50		page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
 51					 NULL);
 52		if (IS_ERR(page))
 53			return PTR_ERR(page);
 54
 55		addr = kmap_atomic(page);
 56		memcpy(buf, addr + offset_in_page(pos), n);
 57		kunmap_atomic(addr);
 58
 59		put_page(page);
 60
 61		buf += n;
 62		pos += n;
 63		count -= n;
 64	}
 65	return 0;
 66}
 67
 68/*
 69 * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
 70 * kernel_write() can't be used because the file descriptor is readonly.
 71 */
 72static int pagecache_write(struct inode *inode, const void *buf, size_t count,
 73			   loff_t pos)
 74{
 75	if (pos + count > inode->i_sb->s_maxbytes)
 76		return -EFBIG;
 77
 78	while (count) {
 79		size_t n = min_t(size_t, count,
 80				 PAGE_SIZE - offset_in_page(pos));
 81		struct page *page;
 82		void *fsdata;
 83		void *addr;
 84		int res;
 85
 86		res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
 87					    &page, &fsdata);
 88		if (res)
 89			return res;
 90
 91		addr = kmap_atomic(page);
 92		memcpy(addr + offset_in_page(pos), buf, n);
 93		kunmap_atomic(addr);
 94
 95		res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
 96					  page, fsdata);
 97		if (res < 0)
 98			return res;
 99		if (res != n)
100			return -EIO;
101
102		buf += n;
103		pos += n;
104		count -= n;
105	}
106	return 0;
107}
108
109static int ext4_begin_enable_verity(struct file *filp)
110{
111	struct inode *inode = file_inode(filp);
112	const int credits = 2; /* superblock and inode for ext4_orphan_add() */
113	handle_t *handle;
114	int err;
115
116	if (ext4_verity_in_progress(inode))
117		return -EBUSY;
118
119	/*
120	 * Since the file was opened readonly, we have to initialize the jbd
121	 * inode and quotas here and not rely on ->open() doing it.  This must
122	 * be done before evicting the inline data.
123	 */
124
125	err = ext4_inode_attach_jinode(inode);
126	if (err)
127		return err;
128
129	err = dquot_initialize(inode);
130	if (err)
131		return err;
132
133	err = ext4_convert_inline_data(inode);
134	if (err)
135		return err;
136
137	if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
138		ext4_warning_inode(inode,
139				   "verity is only allowed on extent-based files");
140		return -EOPNOTSUPP;
141	}
142
143	/*
144	 * ext4 uses the last allocated block to find the verity descriptor, so
145	 * we must remove any other blocks past EOF which might confuse things.
146	 */
147	err = ext4_truncate(inode);
148	if (err)
149		return err;
150
151	handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
152	if (IS_ERR(handle))
153		return PTR_ERR(handle);
154
155	err = ext4_orphan_add(handle, inode);
156	if (err == 0)
157		ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
158
159	ext4_journal_stop(handle);
160	return err;
161}
162
163/*
164 * ext4 stores the verity descriptor beginning on the next filesystem block
165 * boundary after the Merkle tree.  Then, the descriptor size is stored in the
166 * last 4 bytes of the last allocated filesystem block --- which is either the
167 * block in which the descriptor ends, or the next block after that if there
168 * weren't at least 4 bytes remaining.
169 *
170 * We can't simply store the descriptor in an xattr because it *must* be
171 * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
172 * xattrs.  Also, if the descriptor includes a large signature blob it may be
173 * too large to store in an xattr without the EA_INODE feature.
174 */
175static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,
176					size_t desc_size, u64 merkle_tree_size)
177{
178	const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
179				      merkle_tree_size, i_blocksize(inode));
180	const u64 desc_end = desc_pos + desc_size;
181	const __le32 desc_size_disk = cpu_to_le32(desc_size);
182	const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
183					   i_blocksize(inode)) -
184				  sizeof(desc_size_disk);
185	int err;
186
187	err = pagecache_write(inode, desc, desc_size, desc_pos);
188	if (err)
189		return err;
190
191	return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
192			       desc_size_pos);
193}
194
195static int ext4_end_enable_verity(struct file *filp, const void *desc,
196				  size_t desc_size, u64 merkle_tree_size)
197{
198	struct inode *inode = file_inode(filp);
199	const int credits = 2; /* superblock and inode for ext4_orphan_del() */
200	handle_t *handle;
201	int err = 0;
202	int err2;
203
204	if (desc != NULL) {
205		/* Succeeded; write the verity descriptor. */
206		err = ext4_write_verity_descriptor(inode, desc, desc_size,
207						   merkle_tree_size);
208
209		/* Write all pages before clearing VERITY_IN_PROGRESS. */
210		if (!err)
211			err = filemap_write_and_wait(inode->i_mapping);
212	}
213
214	/* If we failed, truncate anything we wrote past i_size. */
215	if (desc == NULL || err)
216		ext4_truncate(inode);
217
218	/*
219	 * We must always clean up by clearing EXT4_STATE_VERITY_IN_PROGRESS and
220	 * deleting the inode from the orphan list, even if something failed.
221	 * If everything succeeded, we'll also set the verity bit in the same
222	 * transaction.
223	 */
224
225	ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
226
227	handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
228	if (IS_ERR(handle)) {
229		ext4_orphan_del(NULL, inode);
230		return PTR_ERR(handle);
231	}
232
233	err2 = ext4_orphan_del(handle, inode);
234	if (err2)
235		goto out_stop;
236
237	if (desc != NULL && !err) {
238		struct ext4_iloc iloc;
239
240		err = ext4_reserve_inode_write(handle, inode, &iloc);
241		if (err)
242			goto out_stop;
243		ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
244		ext4_set_inode_flags(inode);
245		err = ext4_mark_iloc_dirty(handle, inode, &iloc);
246	}
247out_stop:
248	ext4_journal_stop(handle);
249	return err ?: err2;
250}
251
252static int ext4_get_verity_descriptor_location(struct inode *inode,
253					       size_t *desc_size_ret,
254					       u64 *desc_pos_ret)
255{
256	struct ext4_ext_path *path;
257	struct ext4_extent *last_extent;
258	u32 end_lblk;
259	u64 desc_size_pos;
260	__le32 desc_size_disk;
261	u32 desc_size;
262	u64 desc_pos;
263	int err;
264
265	/*
266	 * Descriptor size is in last 4 bytes of last allocated block.
267	 * See ext4_write_verity_descriptor().
268	 */
269
270	if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
271		EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
272		return -EFSCORRUPTED;
273	}
274
275	path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
276	if (IS_ERR(path))
277		return PTR_ERR(path);
278
279	last_extent = path[path->p_depth].p_ext;
280	if (!last_extent) {
281		EXT4_ERROR_INODE(inode, "verity file has no extents");
282		ext4_ext_drop_refs(path);
283		kfree(path);
284		return -EFSCORRUPTED;
285	}
286
287	end_lblk = le32_to_cpu(last_extent->ee_block) +
288		   ext4_ext_get_actual_len(last_extent);
289	desc_size_pos = (u64)end_lblk << inode->i_blkbits;
290	ext4_ext_drop_refs(path);
291	kfree(path);
292
293	if (desc_size_pos < sizeof(desc_size_disk))
294		goto bad;
295	desc_size_pos -= sizeof(desc_size_disk);
296
297	err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
298			     desc_size_pos);
299	if (err)
300		return err;
301	desc_size = le32_to_cpu(desc_size_disk);
302
303	/*
304	 * The descriptor is stored just before the desc_size_disk, but starting
305	 * on a filesystem block boundary.
306	 */
307
308	if (desc_size > INT_MAX || desc_size > desc_size_pos)
309		goto bad;
310
311	desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
312	if (desc_pos < ext4_verity_metadata_pos(inode))
313		goto bad;
314
315	*desc_size_ret = desc_size;
316	*desc_pos_ret = desc_pos;
317	return 0;
318
319bad:
320	EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
321	return -EFSCORRUPTED;
322}
323
324static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
325				      size_t buf_size)
326{
327	size_t desc_size = 0;
328	u64 desc_pos = 0;
329	int err;
330
331	err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
332	if (err)
333		return err;
334
335	if (buf_size) {
336		if (desc_size > buf_size)
337			return -ERANGE;
338		err = pagecache_read(inode, buf, desc_size, desc_pos);
339		if (err)
340			return err;
341	}
342	return desc_size;
343}
344
345static struct page *ext4_read_merkle_tree_page(struct inode *inode,
346					       pgoff_t index)
347{
348	index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
349
350	return read_mapping_page(inode->i_mapping, index, NULL);
351}
352
353static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,
354					u64 index, int log_blocksize)
355{
356	loff_t pos = ext4_verity_metadata_pos(inode) + (index << log_blocksize);
357
358	return pagecache_write(inode, buf, 1 << log_blocksize, pos);
359}
360
361const struct fsverity_operations ext4_verityops = {
362	.begin_enable_verity	= ext4_begin_enable_verity,
363	.end_enable_verity	= ext4_end_enable_verity,
364	.get_verity_descriptor	= ext4_get_verity_descriptor,
365	.read_merkle_tree_page	= ext4_read_merkle_tree_page,
366	.write_merkle_tree_block = ext4_write_merkle_tree_block,
367};