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![Eric Biggers](/assets/img/avatar_default.png)
I originally chose the name "file measurement" to refer to the fs-verity file digest to avoid confusion with traditional full-file digests or with the bare root hash of the Merkle tree. But the name "file measurement" hasn't caught on, and usually people are calling it something else, usually the "file digest". E.g. see "struct fsverity_digest" and "struct fsverity_formatted_digest", the libfsverity_compute_digest() and libfsverity_sign_digest() functions in libfsverity, and the "fsverity digest" command. Having multiple names for the same thing is always confusing. So to hopefully avoid confusion in the future, rename "fs-verity file measurement" to "fs-verity file digest". This leaves FS_IOC_MEASURE_VERITY as the only reference to "measure" in the kernel, which makes some amount of sense since the ioctl is actively "measuring" the file. I'll be renaming this in fsverity-utils too (though similarly the 'fsverity measure' command, which is a wrapper for FS_IOC_MEASURE_VERITY, will stay). Acked-by: Luca Boccassi <luca.boccassi@microsoft.com> Link: https://lore.kernel.org/r/20201113211918.71883-4-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
418 lines
12 KiB
C
418 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Ioctl to enable verity on a file
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*
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* Copyright 2019 Google LLC
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*/
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#include "fsverity_private.h"
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#include <crypto/hash.h>
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#include <linux/backing-dev.h>
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#include <linux/mount.h>
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#include <linux/pagemap.h>
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#include <linux/sched/signal.h>
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#include <linux/uaccess.h>
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/*
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* Read a file data page for Merkle tree construction. Do aggressive readahead,
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* since we're sequentially reading the entire file.
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*/
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static struct page *read_file_data_page(struct file *filp, pgoff_t index,
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struct file_ra_state *ra,
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unsigned long remaining_pages)
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{
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struct page *page;
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page = find_get_page_flags(filp->f_mapping, index, FGP_ACCESSED);
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if (!page || !PageUptodate(page)) {
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if (page)
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put_page(page);
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else
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page_cache_sync_readahead(filp->f_mapping, ra, filp,
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index, remaining_pages);
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page = read_mapping_page(filp->f_mapping, index, NULL);
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if (IS_ERR(page))
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return page;
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}
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if (PageReadahead(page))
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page_cache_async_readahead(filp->f_mapping, ra, filp, page,
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index, remaining_pages);
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return page;
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}
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static int build_merkle_tree_level(struct file *filp, unsigned int level,
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u64 num_blocks_to_hash,
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const struct merkle_tree_params *params,
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u8 *pending_hashes,
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struct ahash_request *req)
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{
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struct inode *inode = file_inode(filp);
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const struct fsverity_operations *vops = inode->i_sb->s_vop;
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struct file_ra_state ra = { 0 };
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unsigned int pending_size = 0;
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u64 dst_block_num;
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u64 i;
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int err;
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if (WARN_ON(params->block_size != PAGE_SIZE)) /* checked earlier too */
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return -EINVAL;
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if (level < params->num_levels) {
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dst_block_num = params->level_start[level];
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} else {
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if (WARN_ON(num_blocks_to_hash != 1))
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return -EINVAL;
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dst_block_num = 0; /* unused */
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}
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file_ra_state_init(&ra, filp->f_mapping);
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for (i = 0; i < num_blocks_to_hash; i++) {
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struct page *src_page;
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if ((pgoff_t)i % 10000 == 0 || i + 1 == num_blocks_to_hash)
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pr_debug("Hashing block %llu of %llu for level %u\n",
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i + 1, num_blocks_to_hash, level);
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if (level == 0) {
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/* Leaf: hashing a data block */
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src_page = read_file_data_page(filp, i, &ra,
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num_blocks_to_hash - i);
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if (IS_ERR(src_page)) {
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err = PTR_ERR(src_page);
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fsverity_err(inode,
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"Error %d reading data page %llu",
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err, i);
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return err;
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}
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} else {
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unsigned long num_ra_pages =
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min_t(unsigned long, num_blocks_to_hash - i,
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inode->i_sb->s_bdi->io_pages);
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/* Non-leaf: hashing hash block from level below */
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src_page = vops->read_merkle_tree_page(inode,
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params->level_start[level - 1] + i,
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num_ra_pages);
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if (IS_ERR(src_page)) {
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err = PTR_ERR(src_page);
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fsverity_err(inode,
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"Error %d reading Merkle tree page %llu",
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err, params->level_start[level - 1] + i);
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return err;
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}
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}
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err = fsverity_hash_page(params, inode, req, src_page,
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&pending_hashes[pending_size]);
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put_page(src_page);
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if (err)
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return err;
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pending_size += params->digest_size;
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if (level == params->num_levels) /* Root hash? */
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return 0;
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if (pending_size + params->digest_size > params->block_size ||
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i + 1 == num_blocks_to_hash) {
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/* Flush the pending hash block */
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memset(&pending_hashes[pending_size], 0,
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params->block_size - pending_size);
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err = vops->write_merkle_tree_block(inode,
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pending_hashes,
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dst_block_num,
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params->log_blocksize);
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if (err) {
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fsverity_err(inode,
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"Error %d writing Merkle tree block %llu",
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err, dst_block_num);
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return err;
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}
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dst_block_num++;
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pending_size = 0;
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}
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if (fatal_signal_pending(current))
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return -EINTR;
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cond_resched();
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}
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return 0;
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}
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/*
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* Build the Merkle tree for the given file using the given parameters, and
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* return the root hash in @root_hash.
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*
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* The tree is written to a filesystem-specific location as determined by the
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* ->write_merkle_tree_block() method. However, the blocks that comprise the
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* tree are the same for all filesystems.
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*/
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static int build_merkle_tree(struct file *filp,
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const struct merkle_tree_params *params,
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u8 *root_hash)
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{
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struct inode *inode = file_inode(filp);
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u8 *pending_hashes;
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struct ahash_request *req;
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u64 blocks;
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unsigned int level;
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int err = -ENOMEM;
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if (inode->i_size == 0) {
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/* Empty file is a special case; root hash is all 0's */
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memset(root_hash, 0, params->digest_size);
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return 0;
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}
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/* This allocation never fails, since it's mempool-backed. */
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req = fsverity_alloc_hash_request(params->hash_alg, GFP_KERNEL);
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pending_hashes = kmalloc(params->block_size, GFP_KERNEL);
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if (!pending_hashes)
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goto out;
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/*
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* Build each level of the Merkle tree, starting at the leaf level
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* (level 0) and ascending to the root node (level 'num_levels - 1').
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* Then at the end (level 'num_levels'), calculate the root hash.
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*/
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blocks = (inode->i_size + params->block_size - 1) >>
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params->log_blocksize;
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for (level = 0; level <= params->num_levels; level++) {
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err = build_merkle_tree_level(filp, level, blocks, params,
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pending_hashes, req);
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if (err)
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goto out;
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blocks = (blocks + params->hashes_per_block - 1) >>
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params->log_arity;
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}
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memcpy(root_hash, pending_hashes, params->digest_size);
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err = 0;
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out:
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kfree(pending_hashes);
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fsverity_free_hash_request(params->hash_alg, req);
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return err;
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}
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static int enable_verity(struct file *filp,
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const struct fsverity_enable_arg *arg)
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{
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struct inode *inode = file_inode(filp);
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const struct fsverity_operations *vops = inode->i_sb->s_vop;
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struct merkle_tree_params params = { };
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struct fsverity_descriptor *desc;
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size_t desc_size = sizeof(*desc) + arg->sig_size;
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struct fsverity_info *vi;
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int err;
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/* Start initializing the fsverity_descriptor */
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desc = kzalloc(desc_size, GFP_KERNEL);
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if (!desc)
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return -ENOMEM;
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desc->version = 1;
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desc->hash_algorithm = arg->hash_algorithm;
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desc->log_blocksize = ilog2(arg->block_size);
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/* Get the salt if the user provided one */
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if (arg->salt_size &&
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copy_from_user(desc->salt, u64_to_user_ptr(arg->salt_ptr),
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arg->salt_size)) {
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err = -EFAULT;
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goto out;
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}
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desc->salt_size = arg->salt_size;
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/* Get the signature if the user provided one */
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if (arg->sig_size &&
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copy_from_user(desc->signature, u64_to_user_ptr(arg->sig_ptr),
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arg->sig_size)) {
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err = -EFAULT;
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goto out;
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}
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desc->sig_size = cpu_to_le32(arg->sig_size);
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desc->data_size = cpu_to_le64(inode->i_size);
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/* Prepare the Merkle tree parameters */
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err = fsverity_init_merkle_tree_params(¶ms, inode,
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arg->hash_algorithm,
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desc->log_blocksize,
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desc->salt, desc->salt_size);
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if (err)
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goto out;
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/*
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* Start enabling verity on this file, serialized by the inode lock.
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* Fail if verity is already enabled or is already being enabled.
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*/
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inode_lock(inode);
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if (IS_VERITY(inode))
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err = -EEXIST;
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else
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err = vops->begin_enable_verity(filp);
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inode_unlock(inode);
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if (err)
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goto out;
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/*
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* Build the Merkle tree. Don't hold the inode lock during this, since
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* on huge files this may take a very long time and we don't want to
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* force unrelated syscalls like chown() to block forever. We don't
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* need the inode lock here because deny_write_access() already prevents
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* the file from being written to or truncated, and we still serialize
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* ->begin_enable_verity() and ->end_enable_verity() using the inode
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* lock and only allow one process to be here at a time on a given file.
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*/
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pr_debug("Building Merkle tree...\n");
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BUILD_BUG_ON(sizeof(desc->root_hash) < FS_VERITY_MAX_DIGEST_SIZE);
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err = build_merkle_tree(filp, ¶ms, desc->root_hash);
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if (err) {
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fsverity_err(inode, "Error %d building Merkle tree", err);
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goto rollback;
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}
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pr_debug("Done building Merkle tree. Root hash is %s:%*phN\n",
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params.hash_alg->name, params.digest_size, desc->root_hash);
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/*
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* Create the fsverity_info. Don't bother trying to save work by
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* reusing the merkle_tree_params from above. Instead, just create the
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* fsverity_info from the fsverity_descriptor as if it were just loaded
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* from disk. This is simpler, and it serves as an extra check that the
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* metadata we're writing is valid before actually enabling verity.
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*/
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vi = fsverity_create_info(inode, desc, desc_size);
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if (IS_ERR(vi)) {
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err = PTR_ERR(vi);
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goto rollback;
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}
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if (arg->sig_size)
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pr_debug("Storing a %u-byte PKCS#7 signature alongside the file\n",
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arg->sig_size);
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/*
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* Tell the filesystem to finish enabling verity on the file.
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* Serialized with ->begin_enable_verity() by the inode lock.
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*/
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inode_lock(inode);
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err = vops->end_enable_verity(filp, desc, desc_size, params.tree_size);
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inode_unlock(inode);
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if (err) {
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fsverity_err(inode, "%ps() failed with err %d",
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vops->end_enable_verity, err);
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fsverity_free_info(vi);
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} else if (WARN_ON(!IS_VERITY(inode))) {
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err = -EINVAL;
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fsverity_free_info(vi);
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} else {
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/* Successfully enabled verity */
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/*
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* Readers can start using ->i_verity_info immediately, so it
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* can't be rolled back once set. So don't set it until just
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* after the filesystem has successfully enabled verity.
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*/
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fsverity_set_info(inode, vi);
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}
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out:
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kfree(params.hashstate);
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kfree(desc);
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return err;
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rollback:
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inode_lock(inode);
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(void)vops->end_enable_verity(filp, NULL, 0, params.tree_size);
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inode_unlock(inode);
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goto out;
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}
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/**
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* fsverity_ioctl_enable() - enable verity on a file
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* @filp: file to enable verity on
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* @uarg: user pointer to fsverity_enable_arg
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*
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* Enable fs-verity on a file. See the "FS_IOC_ENABLE_VERITY" section of
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* Documentation/filesystems/fsverity.rst for the documentation.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fsverity_ioctl_enable(struct file *filp, const void __user *uarg)
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{
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struct inode *inode = file_inode(filp);
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struct fsverity_enable_arg arg;
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int err;
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if (copy_from_user(&arg, uarg, sizeof(arg)))
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return -EFAULT;
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if (arg.version != 1)
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return -EINVAL;
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if (arg.__reserved1 ||
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memchr_inv(arg.__reserved2, 0, sizeof(arg.__reserved2)))
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return -EINVAL;
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if (arg.block_size != PAGE_SIZE)
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return -EINVAL;
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if (arg.salt_size > sizeof_field(struct fsverity_descriptor, salt))
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return -EMSGSIZE;
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if (arg.sig_size > FS_VERITY_MAX_SIGNATURE_SIZE)
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return -EMSGSIZE;
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/*
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* Require a regular file with write access. But the actual fd must
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* still be readonly so that we can lock out all writers. This is
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* needed to guarantee that no writable fds exist to the file once it
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* has verity enabled, and to stabilize the data being hashed.
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*/
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err = inode_permission(inode, MAY_WRITE);
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if (err)
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return err;
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if (IS_APPEND(inode))
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return -EPERM;
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if (S_ISDIR(inode->i_mode))
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return -EISDIR;
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if (!S_ISREG(inode->i_mode))
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return -EINVAL;
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err = mnt_want_write_file(filp);
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if (err) /* -EROFS */
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return err;
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err = deny_write_access(filp);
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if (err) /* -ETXTBSY */
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goto out_drop_write;
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err = enable_verity(filp, &arg);
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if (err)
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goto out_allow_write_access;
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/*
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* Some pages of the file may have been evicted from pagecache after
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* being used in the Merkle tree construction, then read into pagecache
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* again by another process reading from the file concurrently. Since
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* these pages didn't undergo verification against the file digest which
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* fs-verity now claims to be enforcing, we have to wipe the pagecache
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* to ensure that all future reads are verified.
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*/
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filemap_write_and_wait(inode->i_mapping);
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invalidate_inode_pages2(inode->i_mapping);
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/*
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* allow_write_access() is needed to pair with deny_write_access().
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* Regardless, the filesystem won't allow writing to verity files.
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*/
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out_allow_write_access:
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allow_write_access(filp);
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out_drop_write:
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mnt_drop_write_file(filp);
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return err;
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}
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EXPORT_SYMBOL_GPL(fsverity_ioctl_enable);
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