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367 lines
10 KiB
367 lines
10 KiB
// 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 tasks may race to set ->i_verity_info, so use |
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* cmpxchg_release(). This pairs with the smp_load_acquire() in |
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* fsverity_get_info(). I.e., here we publish ->i_verity_info with a |
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* RELEASE barrier so that other tasks can ACQUIRE it. |
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*/ |
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if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL) { |
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/* Lost the race, so free the fsverity_info we allocated. */ |
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fsverity_free_info(vi); |
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/* |
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* Afterwards, the caller may access ->i_verity_info directly, |
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* so make sure to ACQUIRE the winning fsverity_info. |
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*/ |
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(void)fsverity_get_info(inode); |
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} |
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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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* @inode: an inode being evicted |
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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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