1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * fs/f2fs/verity.c: fs-verity support for f2fs
  4 *
  5 * Copyright 2019 Google LLC
  6 */
  7
  8/*
  9 * Implementation of fsverity_operations for f2fs.
 10 *
 11 * Like ext4, f2fs stores the verity metadata (Merkle tree and
 12 * fsverity_descriptor) past the end of the file, starting at the first 64K
 13 * boundary beyond i_size.  This approach works because (a) verity files are
 14 * readonly, and (b) pages fully beyond i_size aren't visible to userspace but
 15 * can be read/written internally by f2fs with only some relatively small
 16 * changes to f2fs.  Extended attributes cannot be used because (a) f2fs limits
 17 * the total size of an inode's xattr entries to 4096 bytes, which wouldn't be
 18 * enough for even a single Merkle tree block, and (b) f2fs encryption doesn't
 19 * encrypt xattrs, yet the verity metadata *must* be encrypted when the file is
 20 * because it contains hashes of the plaintext data.
 21 *
 22 * Using a 64K boundary rather than a 4K one keeps things ready for
 23 * architectures with 64K pages, and it doesn't necessarily waste space on-disk
 24 * since there can be a hole between i_size and the start of the Merkle tree.
 25 */
 26
 27#include <linux/f2fs_fs.h>
 28
 29#include "f2fs.h"
 30#include "xattr.h"
 31
 32static inline loff_t f2fs_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
109/*
110 * Format of f2fs verity xattr.  This points to the location of the verity
111 * descriptor within the file data rather than containing it directly because
112 * the verity descriptor *must* be encrypted when f2fs encryption is used.  But,
113 * f2fs encryption does not encrypt xattrs.
114 */
115struct fsverity_descriptor_location {
116	__le32 version;
117	__le32 size;
118	__le64 pos;
119};
120
121static int f2fs_begin_enable_verity(struct file *filp)
122{
123	struct inode *inode = file_inode(filp);
124	int err;
125
126	if (f2fs_verity_in_progress(inode))
127		return -EBUSY;
128
129	if (f2fs_is_atomic_file(inode) || f2fs_is_volatile_file(inode))
130		return -EOPNOTSUPP;
131
132	/*
133	 * Since the file was opened readonly, we have to initialize the quotas
134	 * here and not rely on ->open() doing it.  This must be done before
135	 * evicting the inline data.
136	 */
137	err = dquot_initialize(inode);
138	if (err)
139		return err;
140
141	err = f2fs_convert_inline_inode(inode);
142	if (err)
143		return err;
144
145	set_inode_flag(inode, FI_VERITY_IN_PROGRESS);
146	return 0;
147}
148
149static int f2fs_end_enable_verity(struct file *filp, const void *desc,
150				  size_t desc_size, u64 merkle_tree_size)
151{
152	struct inode *inode = file_inode(filp);
153	u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
154	struct fsverity_descriptor_location dloc = {
155		.version = cpu_to_le32(1),
156		.size = cpu_to_le32(desc_size),
157		.pos = cpu_to_le64(desc_pos),
158	};
159	int err = 0;
160
161	if (desc != NULL) {
162		/* Succeeded; write the verity descriptor. */
163		err = pagecache_write(inode, desc, desc_size, desc_pos);
164
165		/* Write all pages before clearing FI_VERITY_IN_PROGRESS. */
166		if (!err)
167			err = filemap_write_and_wait(inode->i_mapping);
168	}
169
170	/* If we failed, truncate anything we wrote past i_size. */
171	if (desc == NULL || err)
172		f2fs_truncate(inode);
173
174	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
175
176	if (desc != NULL && !err) {
177		err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
178				    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
179				    NULL, XATTR_CREATE);
180		if (!err) {
181			file_set_verity(inode);
182			f2fs_set_inode_flags(inode);
183			f2fs_mark_inode_dirty_sync(inode, true);
184		}
185	}
186	return err;
187}
188
189static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
190				      size_t buf_size)
191{
192	struct fsverity_descriptor_location dloc;
193	int res;
194	u32 size;
195	u64 pos;
196
197	/* Get the descriptor location */
198	res = f2fs_getxattr(inode, F2FS_XATTR_INDEX_VERITY,
199			    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc), NULL);
200	if (res < 0 && res != -ERANGE)
201		return res;
202	if (res != sizeof(dloc) || dloc.version != cpu_to_le32(1)) {
203		f2fs_warn(F2FS_I_SB(inode), "unknown verity xattr format");
204		return -EINVAL;
205	}
206	size = le32_to_cpu(dloc.size);
207	pos = le64_to_cpu(dloc.pos);
208
209	/* Get the descriptor */
210	if (pos + size < pos || pos + size > inode->i_sb->s_maxbytes ||
211	    pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
212		f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
213		return -EFSCORRUPTED;
214	}
215	if (buf_size) {
216		if (size > buf_size)
217			return -ERANGE;
218		res = pagecache_read(inode, buf, size, pos);
219		if (res)
220			return res;
221	}
222	return size;
223}
224
225static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
226					       pgoff_t index)
227{
228	index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
229
230	return read_mapping_page(inode->i_mapping, index, NULL);
231}
232
233static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
234					u64 index, int log_blocksize)
235{
236	loff_t pos = f2fs_verity_metadata_pos(inode) + (index << log_blocksize);
237
238	return pagecache_write(inode, buf, 1 << log_blocksize, pos);
239}
240
241const struct fsverity_operations f2fs_verityops = {
242	.begin_enable_verity	= f2fs_begin_enable_verity,
243	.end_enable_verity	= f2fs_end_enable_verity,
244	.get_verity_descriptor	= f2fs_get_verity_descriptor,
245	.read_merkle_tree_page	= f2fs_read_merkle_tree_page,
246	.write_merkle_tree_block = f2fs_write_merkle_tree_block,
247};