| // 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; |
| void *addr; |
| |
| page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT, |
| NULL); |
| if (IS_ERR(page)) |
| return PTR_ERR(page); |
| |
| addr = kmap_atomic(page); |
| memcpy(buf, addr + offset_in_page(pos), n); |
| kunmap_atomic(addr); |
| |
| 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) |
| { |
| 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; |
| void *addr; |
| int res; |
| |
| res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0, |
| &page, &fsdata); |
| if (res) |
| return res; |
| |
| addr = kmap_atomic(page); |
| memcpy(addr + offset_in_page(pos), buf, n); |
| kunmap_atomic(addr); |
| |
| res = pagecache_write_end(NULL, inode->i_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 (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); |
| 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_ext_drop_refs(path); |
| kfree(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_ext_drop_refs(path); |
| kfree(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) |
| { |
| index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT; |
| |
| return read_mapping_page(inode->i_mapping, index, NULL); |
| } |
| |
| 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, |
| }; |