426 строки
12 KiB
C
426 строки
12 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* 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/mm.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 blocks_in_level[FS_VERITY_MAX_LEVELS];
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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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/*
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* fs/verity/ directly assumes that the Merkle tree block size is a
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* power of 2 less than or equal to PAGE_SIZE. Another restriction
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* arises from the interaction between fs/verity/ and the filesystems
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* themselves: filesystems expect to be able to verify a single
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* filesystem block of data at a time. Therefore, the Merkle tree block
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* size must also be less than or equal to the filesystem block size.
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*
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* The above are the only hard limitations, so in theory the Merkle tree
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* block size could be as small as twice the digest size. However,
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* that's not useful, and it would result in some unusually deep and
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* large Merkle trees. So we currently require that the Merkle tree
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* block size be at least 1024 bytes. That's small enough to test the
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* sub-page block case on systems with 4K pages, but not too small.
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*/
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if (log_blocksize < 10 || log_blocksize > PAGE_SHIFT ||
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log_blocksize > inode->i_blkbits) {
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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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params->log_blocks_per_page = PAGE_SHIFT - log_blocksize;
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params->blocks_per_page = 1 << params->log_blocks_per_page;
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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_digestsize = ilog2(params->digest_size);
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params->log_arity = log_blocksize - params->log_digestsize;
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params->hashes_per_block = 1 << params->log_arity;
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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 = ((u64)inode->i_size + params->block_size - 1) >> log_blocksize;
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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 = -EFBIG;
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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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blocks_in_level[params->num_levels++] = blocks;
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}
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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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params->level_start[level] = offset;
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offset += blocks_in_level[level];
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}
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/*
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* With block_size != PAGE_SIZE, an in-memory bitmap will need to be
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* allocated to track the "verified" status of hash blocks. Don't allow
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* this bitmap to get too large. For now, limit it to 1 MiB, which
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* limits the file size to about 4.4 TB with SHA-256 and 4K blocks.
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*
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* Together with the fact that the data, and thus also the Merkle tree,
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* cannot have more than ULONG_MAX pages, this implies that hash block
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* indices can always fit in an 'unsigned long'. But to be safe, we
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* explicitly check for that too. Note, this is only for hash block
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* indices; data block indices might not fit in an 'unsigned long'.
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*/
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if ((params->block_size != PAGE_SIZE && offset > 1 << 23) ||
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offset > ULONG_MAX) {
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fsverity_err(inode, "Too many blocks in Merkle tree");
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err = -EFBIG;
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goto out_err;
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}
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params->tree_size = offset << log_blocksize;
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params->tree_pages = PAGE_ALIGN(params->tree_size) >> PAGE_SHIFT;
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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 digest 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_digest(struct fsverity_hash_alg *hash_alg,
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struct fsverity_descriptor *desc,
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u8 *file_digest)
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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), file_digest);
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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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* Create a new fsverity_info from the given fsverity_descriptor (with optional
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* appended signature), and check the signature if present. The
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* fsverity_descriptor must have already undergone basic validation.
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*/
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struct fsverity_info *fsverity_create_info(const struct inode *inode,
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struct fsverity_descriptor *desc)
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{
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struct fsverity_info *vi;
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int err;
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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 fail;
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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_digest(vi->tree_params.hash_alg, desc,
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vi->file_digest);
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if (err) {
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fsverity_err(inode, "Error %d computing file digest", err);
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goto fail;
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}
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err = fsverity_verify_signature(vi, desc->signature,
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le32_to_cpu(desc->sig_size));
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if (err)
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goto fail;
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if (vi->tree_params.block_size != PAGE_SIZE) {
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/*
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* When the Merkle tree block size and page size differ, we use
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* a bitmap to keep track of which hash blocks have been
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* verified. This bitmap must contain one bit per hash block,
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* including alignment to a page boundary at the end.
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*
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* Eventually, to support extremely large files in an efficient
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* way, it might be necessary to make pages of this bitmap
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* reclaimable. But for now, simply allocating the whole bitmap
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* is a simple solution that works well on the files on which
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* fsverity is realistically used. E.g., with SHA-256 and 4K
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* blocks, a 100MB file only needs a 24-byte bitmap, and the
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* bitmap for any file under 17GB fits in a 4K page.
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*/
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unsigned long num_bits =
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vi->tree_params.tree_pages <<
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vi->tree_params.log_blocks_per_page;
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vi->hash_block_verified = kvcalloc(BITS_TO_LONGS(num_bits),
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sizeof(unsigned long),
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GFP_KERNEL);
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if (!vi->hash_block_verified) {
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err = -ENOMEM;
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goto fail;
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}
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spin_lock_init(&vi->hash_page_init_lock);
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}
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return vi;
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fail:
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fsverity_free_info(vi);
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return ERR_PTR(err);
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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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kvfree(vi->hash_block_verified);
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kmem_cache_free(fsverity_info_cachep, vi);
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}
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static bool validate_fsverity_descriptor(struct inode *inode,
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const struct fsverity_descriptor *desc,
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size_t desc_size)
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{
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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 false;
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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 false;
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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 false;
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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 false;
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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 false;
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}
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if (le32_to_cpu(desc->sig_size) > desc_size - sizeof(*desc)) {
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fsverity_err(inode, "Signature overflows verity descriptor");
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return false;
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}
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return true;
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}
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/*
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* Read the inode's fsverity_descriptor (with optional appended signature) from
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* the filesystem, and do basic validation of it.
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*/
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int fsverity_get_descriptor(struct inode *inode,
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struct fsverity_descriptor **desc_ret)
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{
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int res;
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struct fsverity_descriptor *desc;
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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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kfree(desc);
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return res;
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}
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if (!validate_fsverity_descriptor(inode, desc, res)) {
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kfree(desc);
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return -EINVAL;
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}
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*desc_ret = desc;
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return 0;
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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 err;
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if (vi)
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return 0;
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err = fsverity_get_descriptor(inode, &desc);
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if (err)
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return err;
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vi = fsverity_create_info(inode, desc);
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if (IS_ERR(vi)) {
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err = 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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err = 0;
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out_free_desc:
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kfree(desc);
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return err;
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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 (filp->f_mode & FMODE_WRITE)
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return -EPERM;
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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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int __fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
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{
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if (attr->ia_valid & ATTR_SIZE)
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return -EPERM;
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return 0;
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}
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EXPORT_SYMBOL_GPL(__fsverity_prepare_setattr);
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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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file_digest);
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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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