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![Eric Biggers](/assets/img/avatar_default.png)
When initializing an fs-verity hash algorithm, also initialize a mempool that contains a single preallocated hash request object. Then replace the direct calls to ahash_request_alloc() and ahash_request_free() with allocating and freeing from this mempool. This eliminates the possibility of the allocation failing, which is desirable for the I/O path. This doesn't cause deadlocks because there's no case where multiple hash requests are needed at a time to make forward progress. Link: https://lore.kernel.org/r/20191231175545.20709-1-ebiggers@kernel.org Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Eric Biggers <ebiggers@google.com>
357 lines
9.7 KiB
C
357 lines
9.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* fs/verity/open.c: opening fs-verity files
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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 <linux/slab.h>
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static struct kmem_cache *fsverity_info_cachep;
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/**
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* fsverity_init_merkle_tree_params() - initialize Merkle tree parameters
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* @params: the parameters struct to initialize
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* @inode: the inode for which the Merkle tree is being built
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* @hash_algorithm: number of hash algorithm to use
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* @log_blocksize: log base 2 of block size to use
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* @salt: pointer to salt (optional)
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* @salt_size: size of salt, possibly 0
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*
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* Validate the hash algorithm and block size, then compute the tree topology
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* (num levels, num blocks in each level, etc.) and initialize @params.
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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_init_merkle_tree_params(struct merkle_tree_params *params,
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const struct inode *inode,
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unsigned int hash_algorithm,
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unsigned int log_blocksize,
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const u8 *salt, size_t salt_size)
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{
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struct fsverity_hash_alg *hash_alg;
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int err;
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u64 blocks;
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u64 offset;
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int level;
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memset(params, 0, sizeof(*params));
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hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
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if (IS_ERR(hash_alg))
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return PTR_ERR(hash_alg);
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params->hash_alg = hash_alg;
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params->digest_size = hash_alg->digest_size;
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params->hashstate = fsverity_prepare_hash_state(hash_alg, salt,
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salt_size);
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if (IS_ERR(params->hashstate)) {
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err = PTR_ERR(params->hashstate);
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params->hashstate = NULL;
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fsverity_err(inode, "Error %d preparing hash state", err);
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goto out_err;
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}
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if (log_blocksize != PAGE_SHIFT) {
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fsverity_warn(inode, "Unsupported log_blocksize: %u",
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log_blocksize);
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err = -EINVAL;
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goto out_err;
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}
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params->log_blocksize = log_blocksize;
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params->block_size = 1 << log_blocksize;
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if (WARN_ON(!is_power_of_2(params->digest_size))) {
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err = -EINVAL;
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goto out_err;
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}
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if (params->block_size < 2 * params->digest_size) {
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fsverity_warn(inode,
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"Merkle tree block size (%u) too small for hash algorithm \"%s\"",
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params->block_size, hash_alg->name);
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err = -EINVAL;
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goto out_err;
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}
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params->log_arity = params->log_blocksize - ilog2(params->digest_size);
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params->hashes_per_block = 1 << params->log_arity;
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pr_debug("Merkle tree uses %s with %u-byte blocks (%u hashes/block), salt=%*phN\n",
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hash_alg->name, params->block_size, params->hashes_per_block,
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(int)salt_size, salt);
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/*
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* Compute the number of levels in the Merkle tree and create a map from
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* level to the starting block of that level. Level 'num_levels - 1' is
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* the root and is stored first. Level 0 is the level directly "above"
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* the data blocks and is stored last.
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*/
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/* Compute number of levels and the number of blocks in each level */
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blocks = (inode->i_size + params->block_size - 1) >> log_blocksize;
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pr_debug("Data is %lld bytes (%llu blocks)\n", inode->i_size, blocks);
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while (blocks > 1) {
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if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
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fsverity_err(inode, "Too many levels in Merkle tree");
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err = -EINVAL;
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goto out_err;
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}
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blocks = (blocks + params->hashes_per_block - 1) >>
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params->log_arity;
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/* temporarily using level_start[] to store blocks in level */
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params->level_start[params->num_levels++] = blocks;
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}
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params->level0_blocks = params->level_start[0];
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/* Compute the starting block of each level */
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offset = 0;
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for (level = (int)params->num_levels - 1; level >= 0; level--) {
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blocks = params->level_start[level];
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params->level_start[level] = offset;
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pr_debug("Level %d is %llu blocks starting at index %llu\n",
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level, blocks, offset);
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offset += blocks;
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}
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params->tree_size = offset << log_blocksize;
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return 0;
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out_err:
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kfree(params->hashstate);
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memset(params, 0, sizeof(*params));
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return err;
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}
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/*
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* Compute the file measurement by hashing the fsverity_descriptor excluding the
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* signature and with the sig_size field set to 0.
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*/
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static int compute_file_measurement(struct fsverity_hash_alg *hash_alg,
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struct fsverity_descriptor *desc,
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u8 *measurement)
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{
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__le32 sig_size = desc->sig_size;
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int err;
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desc->sig_size = 0;
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err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), measurement);
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desc->sig_size = sig_size;
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return err;
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}
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/*
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* Validate the given fsverity_descriptor and create a new fsverity_info from
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* it. The signature (if present) is also checked.
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*/
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struct fsverity_info *fsverity_create_info(const struct inode *inode,
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void *_desc, size_t desc_size)
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{
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struct fsverity_descriptor *desc = _desc;
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struct fsverity_info *vi;
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int err;
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if (desc_size < sizeof(*desc)) {
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fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
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desc_size);
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return ERR_PTR(-EINVAL);
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}
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if (desc->version != 1) {
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fsverity_err(inode, "Unrecognized descriptor version: %u",
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desc->version);
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return ERR_PTR(-EINVAL);
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}
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if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
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fsverity_err(inode, "Reserved bits set in descriptor");
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return ERR_PTR(-EINVAL);
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}
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if (desc->salt_size > sizeof(desc->salt)) {
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fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
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return ERR_PTR(-EINVAL);
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}
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if (le64_to_cpu(desc->data_size) != inode->i_size) {
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fsverity_err(inode,
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"Wrong data_size: %llu (desc) != %lld (inode)",
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le64_to_cpu(desc->data_size), inode->i_size);
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return ERR_PTR(-EINVAL);
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}
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vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL);
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if (!vi)
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return ERR_PTR(-ENOMEM);
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vi->inode = inode;
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err = fsverity_init_merkle_tree_params(&vi->tree_params, inode,
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desc->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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fsverity_err(inode,
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"Error %d initializing Merkle tree parameters",
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err);
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goto out;
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}
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memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
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err = compute_file_measurement(vi->tree_params.hash_alg, desc,
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vi->measurement);
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if (err) {
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fsverity_err(inode, "Error %d computing file measurement", err);
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goto out;
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}
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pr_debug("Computed file measurement: %s:%*phN\n",
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vi->tree_params.hash_alg->name,
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vi->tree_params.digest_size, vi->measurement);
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err = fsverity_verify_signature(vi, desc, desc_size);
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out:
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if (err) {
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fsverity_free_info(vi);
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vi = ERR_PTR(err);
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}
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return vi;
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}
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void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
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{
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/*
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* Multiple processes may race to set ->i_verity_info, so use cmpxchg.
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* This pairs with the READ_ONCE() in fsverity_get_info().
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*/
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if (cmpxchg(&inode->i_verity_info, NULL, vi) != NULL)
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fsverity_free_info(vi);
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}
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void fsverity_free_info(struct fsverity_info *vi)
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{
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if (!vi)
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return;
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kfree(vi->tree_params.hashstate);
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kmem_cache_free(fsverity_info_cachep, vi);
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}
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/* Ensure the inode has an ->i_verity_info */
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static int ensure_verity_info(struct inode *inode)
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{
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struct fsverity_info *vi = fsverity_get_info(inode);
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struct fsverity_descriptor *desc;
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int res;
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if (vi)
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return 0;
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res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
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if (res < 0) {
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fsverity_err(inode,
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"Error %d getting verity descriptor size", res);
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return res;
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}
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if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
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fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
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res);
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return -EMSGSIZE;
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}
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desc = kmalloc(res, GFP_KERNEL);
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if (!desc)
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return -ENOMEM;
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res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
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if (res < 0) {
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fsverity_err(inode, "Error %d reading verity descriptor", res);
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goto out_free_desc;
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}
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vi = fsverity_create_info(inode, desc, res);
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if (IS_ERR(vi)) {
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res = PTR_ERR(vi);
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goto out_free_desc;
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}
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fsverity_set_info(inode, vi);
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res = 0;
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out_free_desc:
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kfree(desc);
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return res;
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}
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/**
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* fsverity_file_open() - prepare to open a verity file
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* @inode: the inode being opened
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* @filp: the struct file being set up
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*
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* When opening a verity file, deny the open if it is for writing. Otherwise,
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* set up the inode's ->i_verity_info if not already done.
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*
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* When combined with fscrypt, this must be called after fscrypt_file_open().
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* Otherwise, we won't have the key set up to decrypt the verity metadata.
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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_file_open(struct inode *inode, struct file *filp)
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{
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if (!IS_VERITY(inode))
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return 0;
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if (filp->f_mode & FMODE_WRITE) {
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pr_debug("Denying opening verity file (ino %lu) for write\n",
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inode->i_ino);
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return -EPERM;
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}
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return ensure_verity_info(inode);
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}
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EXPORT_SYMBOL_GPL(fsverity_file_open);
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/**
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* fsverity_prepare_setattr() - prepare to change a verity inode's attributes
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* @dentry: dentry through which the inode is being changed
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* @attr: attributes to change
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*
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* Verity files are immutable, so deny truncates. This isn't covered by the
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* open-time check because sys_truncate() takes a path, not a file descriptor.
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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_prepare_setattr(struct dentry *dentry, struct iattr *attr)
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{
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if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) {
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pr_debug("Denying truncate of verity file (ino %lu)\n",
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d_inode(dentry)->i_ino);
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return -EPERM;
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}
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return 0;
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}
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EXPORT_SYMBOL_GPL(fsverity_prepare_setattr);
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/**
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* fsverity_cleanup_inode() - free the inode's verity info, if present
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*
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* Filesystems must call this on inode eviction to free ->i_verity_info.
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*/
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void fsverity_cleanup_inode(struct inode *inode)
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{
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fsverity_free_info(inode->i_verity_info);
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inode->i_verity_info = NULL;
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}
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EXPORT_SYMBOL_GPL(fsverity_cleanup_inode);
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int __init fsverity_init_info_cache(void)
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{
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fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info,
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SLAB_RECLAIM_ACCOUNT,
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measurement);
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if (!fsverity_info_cachep)
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return -ENOMEM;
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return 0;
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}
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void __init fsverity_exit_info_cache(void)
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{
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kmem_cache_destroy(fsverity_info_cachep);
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fsverity_info_cachep = NULL;
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}
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