diff options
Diffstat (limited to 'fs/ext4/verity.c')
| -rw-r--r-- | fs/ext4/verity.c | 397 |
1 files changed, 397 insertions, 0 deletions
diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c new file mode 100644 index 000000000..30e3b6579 --- /dev/null +++ b/fs/ext4/verity.c @@ -0,0 +1,397 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * fs/ext4/verity.c: fs-verity support for ext4 + * + * Copyright 2019 Google LLC + */ + +/* + * Implementation of fsverity_operations for ext4. + * + * ext4 stores the verity metadata (Merkle tree and fsverity_descriptor) past + * the end of the file, starting at the first 64K boundary beyond i_size. This + * approach works because (a) verity files are readonly, and (b) pages fully + * beyond i_size aren't visible to userspace but can be read/written internally + * by ext4 with only some relatively small changes to ext4. This approach + * avoids having to depend on the EA_INODE feature and on rearchitecturing + * ext4's xattr support to support paging multi-gigabyte xattrs into memory, and + * to support encrypting xattrs. Note that the verity metadata *must* be + * encrypted when the file is, since it contains hashes of the plaintext data. + * + * Using a 64K boundary rather than a 4K one keeps things ready for + * architectures with 64K pages, and it doesn't necessarily waste space on-disk + * since there can be a hole between i_size and the start of the Merkle tree. + */ + +#include <linux/quotaops.h> + +#include "ext4.h" +#include "ext4_extents.h" +#include "ext4_jbd2.h" + +static inline loff_t ext4_verity_metadata_pos(const struct inode *inode) +{ + return round_up(inode->i_size, 65536); +} + +/* + * Read some verity metadata from the inode. __vfs_read() can't be used because + * we need to read beyond i_size. + */ +static int pagecache_read(struct inode *inode, void *buf, size_t count, + loff_t pos) +{ + while (count) { + size_t n = min_t(size_t, count, + PAGE_SIZE - offset_in_page(pos)); + struct page *page; + + page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT, + NULL); + if (IS_ERR(page)) + return PTR_ERR(page); + + memcpy_from_page(buf, page, offset_in_page(pos), n); + + put_page(page); + + buf += n; + pos += n; + count -= n; + } + return 0; +} + +/* + * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY. + * kernel_write() can't be used because the file descriptor is readonly. + */ +static int pagecache_write(struct inode *inode, const void *buf, size_t count, + loff_t pos) +{ + struct address_space *mapping = inode->i_mapping; + const struct address_space_operations *aops = mapping->a_ops; + + if (pos + count > inode->i_sb->s_maxbytes) + return -EFBIG; + + while (count) { + size_t n = min_t(size_t, count, + PAGE_SIZE - offset_in_page(pos)); + struct page *page; + void *fsdata = NULL; + int res; + + res = aops->write_begin(NULL, mapping, pos, n, &page, &fsdata); + if (res) + return res; + + memcpy_to_page(page, offset_in_page(pos), buf, n); + + res = aops->write_end(NULL, mapping, pos, n, n, page, fsdata); + if (res < 0) + return res; + if (res != n) + return -EIO; + + buf += n; + pos += n; + count -= n; + } + return 0; +} + +static int ext4_begin_enable_verity(struct file *filp) +{ + struct inode *inode = file_inode(filp); + const int credits = 2; /* superblock and inode for ext4_orphan_add() */ + handle_t *handle; + int err; + + if (IS_DAX(inode) || ext4_test_inode_flag(inode, EXT4_INODE_DAX)) + return -EINVAL; + + if (ext4_verity_in_progress(inode)) + return -EBUSY; + + /* + * Since the file was opened readonly, we have to initialize the jbd + * inode and quotas here and not rely on ->open() doing it. This must + * be done before evicting the inline data. + */ + + err = ext4_inode_attach_jinode(inode); + if (err) + return err; + + err = dquot_initialize(inode); + if (err) + return err; + + err = ext4_convert_inline_data(inode); + if (err) + return err; + + if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) { + ext4_warning_inode(inode, + "verity is only allowed on extent-based files"); + return -EOPNOTSUPP; + } + + /* + * ext4 uses the last allocated block to find the verity descriptor, so + * we must remove any other blocks past EOF which might confuse things. + */ + err = ext4_truncate(inode); + if (err) + return err; + + handle = ext4_journal_start(inode, EXT4_HT_INODE, credits); + if (IS_ERR(handle)) + return PTR_ERR(handle); + + err = ext4_orphan_add(handle, inode); + if (err == 0) + ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS); + + ext4_journal_stop(handle); + return err; +} + +/* + * ext4 stores the verity descriptor beginning on the next filesystem block + * boundary after the Merkle tree. Then, the descriptor size is stored in the + * last 4 bytes of the last allocated filesystem block --- which is either the + * block in which the descriptor ends, or the next block after that if there + * weren't at least 4 bytes remaining. + * + * We can't simply store the descriptor in an xattr because it *must* be + * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt + * xattrs. Also, if the descriptor includes a large signature blob it may be + * too large to store in an xattr without the EA_INODE feature. + */ +static int ext4_write_verity_descriptor(struct inode *inode, const void *desc, + size_t desc_size, u64 merkle_tree_size) +{ + const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) + + merkle_tree_size, i_blocksize(inode)); + const u64 desc_end = desc_pos + desc_size; + const __le32 desc_size_disk = cpu_to_le32(desc_size); + const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk), + i_blocksize(inode)) - + sizeof(desc_size_disk); + int err; + + err = pagecache_write(inode, desc, desc_size, desc_pos); + if (err) + return err; + + return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk), + desc_size_pos); +} + +static int ext4_end_enable_verity(struct file *filp, const void *desc, + size_t desc_size, u64 merkle_tree_size) +{ + struct inode *inode = file_inode(filp); + const int credits = 2; /* superblock and inode for ext4_orphan_del() */ + handle_t *handle; + struct ext4_iloc iloc; + int err = 0; + + /* + * If an error already occurred (which fs/verity/ signals by passing + * desc == NULL), then only clean-up is needed. + */ + if (desc == NULL) + goto cleanup; + + /* Append the verity descriptor. */ + err = ext4_write_verity_descriptor(inode, desc, desc_size, + merkle_tree_size); + if (err) + goto cleanup; + + /* + * Write all pages (both data and verity metadata). Note that this must + * happen before clearing EXT4_STATE_VERITY_IN_PROGRESS; otherwise pages + * beyond i_size won't be written properly. For crash consistency, this + * also must happen before the verity inode flag gets persisted. + */ + err = filemap_write_and_wait(inode->i_mapping); + if (err) + goto cleanup; + + /* + * Finally, set the verity inode flag and remove the inode from the + * orphan list (in a single transaction). + */ + + handle = ext4_journal_start(inode, EXT4_HT_INODE, credits); + if (IS_ERR(handle)) { + err = PTR_ERR(handle); + goto cleanup; + } + + err = ext4_orphan_del(handle, inode); + if (err) + goto stop_and_cleanup; + + err = ext4_reserve_inode_write(handle, inode, &iloc); + if (err) + goto stop_and_cleanup; + + ext4_set_inode_flag(inode, EXT4_INODE_VERITY); + ext4_set_inode_flags(inode, false); + err = ext4_mark_iloc_dirty(handle, inode, &iloc); + if (err) + goto stop_and_cleanup; + + ext4_journal_stop(handle); + + ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS); + return 0; + +stop_and_cleanup: + ext4_journal_stop(handle); +cleanup: + /* + * Verity failed to be enabled, so clean up by truncating any verity + * metadata that was written beyond i_size (both from cache and from + * disk), removing the inode from the orphan list (if it wasn't done + * already), and clearing EXT4_STATE_VERITY_IN_PROGRESS. + */ + truncate_inode_pages(inode->i_mapping, inode->i_size); + ext4_truncate(inode); + ext4_orphan_del(NULL, inode); + ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS); + return err; +} + +static int ext4_get_verity_descriptor_location(struct inode *inode, + size_t *desc_size_ret, + u64 *desc_pos_ret) +{ + struct ext4_ext_path *path; + struct ext4_extent *last_extent; + u32 end_lblk; + u64 desc_size_pos; + __le32 desc_size_disk; + u32 desc_size; + u64 desc_pos; + int err; + + /* + * Descriptor size is in last 4 bytes of last allocated block. + * See ext4_write_verity_descriptor(). + */ + + if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) { + EXT4_ERROR_INODE(inode, "verity file doesn't use extents"); + return -EFSCORRUPTED; + } + + path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0); + if (IS_ERR(path)) + return PTR_ERR(path); + + last_extent = path[path->p_depth].p_ext; + if (!last_extent) { + EXT4_ERROR_INODE(inode, "verity file has no extents"); + ext4_free_ext_path(path); + return -EFSCORRUPTED; + } + + end_lblk = le32_to_cpu(last_extent->ee_block) + + ext4_ext_get_actual_len(last_extent); + desc_size_pos = (u64)end_lblk << inode->i_blkbits; + ext4_free_ext_path(path); + + if (desc_size_pos < sizeof(desc_size_disk)) + goto bad; + desc_size_pos -= sizeof(desc_size_disk); + + err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk), + desc_size_pos); + if (err) + return err; + desc_size = le32_to_cpu(desc_size_disk); + + /* + * The descriptor is stored just before the desc_size_disk, but starting + * on a filesystem block boundary. + */ + + if (desc_size > INT_MAX || desc_size > desc_size_pos) + goto bad; + + desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode)); + if (desc_pos < ext4_verity_metadata_pos(inode)) + goto bad; + + *desc_size_ret = desc_size; + *desc_pos_ret = desc_pos; + return 0; + +bad: + EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor"); + return -EFSCORRUPTED; +} + +static int ext4_get_verity_descriptor(struct inode *inode, void *buf, + size_t buf_size) +{ + size_t desc_size = 0; + u64 desc_pos = 0; + int err; + + err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos); + if (err) + return err; + + if (buf_size) { + if (desc_size > buf_size) + return -ERANGE; + err = pagecache_read(inode, buf, desc_size, desc_pos); + if (err) + return err; + } + return desc_size; +} + +static struct page *ext4_read_merkle_tree_page(struct inode *inode, + pgoff_t index, + unsigned long num_ra_pages) +{ + struct page *page; + + index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT; + + page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED); + if (!page || !PageUptodate(page)) { + DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index); + + if (page) + put_page(page); + else if (num_ra_pages > 1) + page_cache_ra_unbounded(&ractl, num_ra_pages, 0); + page = read_mapping_page(inode->i_mapping, index, NULL); + } + return page; +} + +static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf, + u64 index, int log_blocksize) +{ + loff_t pos = ext4_verity_metadata_pos(inode) + (index << log_blocksize); + + return pagecache_write(inode, buf, 1 << log_blocksize, pos); +} + +const struct fsverity_operations ext4_verityops = { + .begin_enable_verity = ext4_begin_enable_verity, + .end_enable_verity = ext4_end_enable_verity, + .get_verity_descriptor = ext4_get_verity_descriptor, + .read_merkle_tree_page = ext4_read_merkle_tree_page, + .write_merkle_tree_block = ext4_write_merkle_tree_block, +}; |