diff options
Diffstat (limited to 'fs/verity/open.c')
| -rw-r--r-- | fs/verity/open.c | 356 |
1 files changed, 356 insertions, 0 deletions
diff --git a/fs/verity/open.c b/fs/verity/open.c new file mode 100644 index 000000000000..63d1004b688c --- /dev/null +++ b/fs/verity/open.c @@ -0,0 +1,356 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * fs/verity/open.c: opening fs-verity files + * + * Copyright 2019 Google LLC + */ + +#include "fsverity_private.h" + +#include <linux/slab.h> + +static struct kmem_cache *fsverity_info_cachep; + +/** + * fsverity_init_merkle_tree_params() - initialize Merkle tree parameters + * @params: the parameters struct to initialize + * @inode: the inode for which the Merkle tree is being built + * @hash_algorithm: number of hash algorithm to use + * @log_blocksize: log base 2 of block size to use + * @salt: pointer to salt (optional) + * @salt_size: size of salt, possibly 0 + * + * Validate the hash algorithm and block size, then compute the tree topology + * (num levels, num blocks in each level, etc.) and initialize @params. + * + * Return: 0 on success, -errno on failure + */ +int fsverity_init_merkle_tree_params(struct merkle_tree_params *params, + const struct inode *inode, + unsigned int hash_algorithm, + unsigned int log_blocksize, + const u8 *salt, size_t salt_size) +{ + const struct fsverity_hash_alg *hash_alg; + int err; + u64 blocks; + u64 offset; + int level; + + memset(params, 0, sizeof(*params)); + + hash_alg = fsverity_get_hash_alg(inode, hash_algorithm); + if (IS_ERR(hash_alg)) + return PTR_ERR(hash_alg); + params->hash_alg = hash_alg; + params->digest_size = hash_alg->digest_size; + + params->hashstate = fsverity_prepare_hash_state(hash_alg, salt, + salt_size); + if (IS_ERR(params->hashstate)) { + err = PTR_ERR(params->hashstate); + params->hashstate = NULL; + fsverity_err(inode, "Error %d preparing hash state", err); + goto out_err; + } + + if (log_blocksize != PAGE_SHIFT) { + fsverity_warn(inode, "Unsupported log_blocksize: %u", + log_blocksize); + err = -EINVAL; + goto out_err; + } + params->log_blocksize = log_blocksize; + params->block_size = 1 << log_blocksize; + + if (WARN_ON(!is_power_of_2(params->digest_size))) { + err = -EINVAL; + goto out_err; + } + if (params->block_size < 2 * params->digest_size) { + fsverity_warn(inode, + "Merkle tree block size (%u) too small for hash algorithm \"%s\"", + params->block_size, hash_alg->name); + err = -EINVAL; + goto out_err; + } + params->log_arity = params->log_blocksize - ilog2(params->digest_size); + params->hashes_per_block = 1 << params->log_arity; + + pr_debug("Merkle tree uses %s with %u-byte blocks (%u hashes/block), salt=%*phN\n", + hash_alg->name, params->block_size, params->hashes_per_block, + (int)salt_size, salt); + + /* + * Compute the number of levels in the Merkle tree and create a map from + * level to the starting block of that level. Level 'num_levels - 1' is + * the root and is stored first. Level 0 is the level directly "above" + * the data blocks and is stored last. + */ + + /* Compute number of levels and the number of blocks in each level */ + blocks = (inode->i_size + params->block_size - 1) >> log_blocksize; + pr_debug("Data is %lld bytes (%llu blocks)\n", inode->i_size, blocks); + while (blocks > 1) { + if (params->num_levels >= FS_VERITY_MAX_LEVELS) { + fsverity_err(inode, "Too many levels in Merkle tree"); + err = -EINVAL; + goto out_err; + } + blocks = (blocks + params->hashes_per_block - 1) >> + params->log_arity; + /* temporarily using level_start[] to store blocks in level */ + params->level_start[params->num_levels++] = blocks; + } + + /* Compute the starting block of each level */ + offset = 0; + for (level = (int)params->num_levels - 1; level >= 0; level--) { + blocks = params->level_start[level]; + params->level_start[level] = offset; + pr_debug("Level %d is %llu blocks starting at index %llu\n", + level, blocks, offset); + offset += blocks; + } + + params->tree_size = offset << log_blocksize; + return 0; + +out_err: + kfree(params->hashstate); + memset(params, 0, sizeof(*params)); + return err; +} + +/* + * Compute the file measurement by hashing the fsverity_descriptor excluding the + * signature and with the sig_size field set to 0. + */ +static int compute_file_measurement(const struct fsverity_hash_alg *hash_alg, + struct fsverity_descriptor *desc, + u8 *measurement) +{ + __le32 sig_size = desc->sig_size; + int err; + + desc->sig_size = 0; + err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), measurement); + desc->sig_size = sig_size; + + return err; +} + +/* + * Validate the given fsverity_descriptor and create a new fsverity_info from + * it. The signature (if present) is also checked. + */ +struct fsverity_info *fsverity_create_info(const struct inode *inode, + void *_desc, size_t desc_size) +{ + struct fsverity_descriptor *desc = _desc; + struct fsverity_info *vi; + int err; + + if (desc_size < sizeof(*desc)) { + fsverity_err(inode, "Unrecognized descriptor size: %zu bytes", + desc_size); + return ERR_PTR(-EINVAL); + } + + if (desc->version != 1) { + fsverity_err(inode, "Unrecognized descriptor version: %u", + desc->version); + return ERR_PTR(-EINVAL); + } + + if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) { + fsverity_err(inode, "Reserved bits set in descriptor"); + return ERR_PTR(-EINVAL); + } + + if (desc->salt_size > sizeof(desc->salt)) { + fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size); + return ERR_PTR(-EINVAL); + } + + if (le64_to_cpu(desc->data_size) != inode->i_size) { + fsverity_err(inode, + "Wrong data_size: %llu (desc) != %lld (inode)", + le64_to_cpu(desc->data_size), inode->i_size); + return ERR_PTR(-EINVAL); + } + + vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL); + if (!vi) + return ERR_PTR(-ENOMEM); + vi->inode = inode; + + err = fsverity_init_merkle_tree_params(&vi->tree_params, inode, + desc->hash_algorithm, + desc->log_blocksize, + desc->salt, desc->salt_size); + if (err) { + fsverity_err(inode, + "Error %d initializing Merkle tree parameters", + err); + goto out; + } + + memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size); + + err = compute_file_measurement(vi->tree_params.hash_alg, desc, + vi->measurement); + if (err) { + fsverity_err(inode, "Error %d computing file measurement", err); + goto out; + } + pr_debug("Computed file measurement: %s:%*phN\n", + vi->tree_params.hash_alg->name, + vi->tree_params.digest_size, vi->measurement); + + err = fsverity_verify_signature(vi, desc, desc_size); +out: + if (err) { + fsverity_free_info(vi); + vi = ERR_PTR(err); + } + return vi; +} + +void fsverity_set_info(struct inode *inode, struct fsverity_info *vi) +{ + /* + * Multiple processes may race to set ->i_verity_info, so use cmpxchg. + * This pairs with the READ_ONCE() in fsverity_get_info(). + */ + if (cmpxchg(&inode->i_verity_info, NULL, vi) != NULL) + fsverity_free_info(vi); +} + +void fsverity_free_info(struct fsverity_info *vi) +{ + if (!vi) + return; + kfree(vi->tree_params.hashstate); + kmem_cache_free(fsverity_info_cachep, vi); +} + +/* Ensure the inode has an ->i_verity_info */ +static int ensure_verity_info(struct inode *inode) +{ + struct fsverity_info *vi = fsverity_get_info(inode); + struct fsverity_descriptor *desc; + int res; + + if (vi) + return 0; + + res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0); + if (res < 0) { + fsverity_err(inode, + "Error %d getting verity descriptor size", res); + return res; + } + if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) { + fsverity_err(inode, "Verity descriptor is too large (%d bytes)", + res); + return -EMSGSIZE; + } + desc = kmalloc(res, GFP_KERNEL); + if (!desc) + return -ENOMEM; + res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res); + if (res < 0) { + fsverity_err(inode, "Error %d reading verity descriptor", res); + goto out_free_desc; + } + + vi = fsverity_create_info(inode, desc, res); + if (IS_ERR(vi)) { + res = PTR_ERR(vi); + goto out_free_desc; + } + + fsverity_set_info(inode, vi); + res = 0; +out_free_desc: + kfree(desc); + return res; +} + +/** + * fsverity_file_open() - prepare to open a verity file + * @inode: the inode being opened + * @filp: the struct file being set up + * + * When opening a verity file, deny the open if it is for writing. Otherwise, + * set up the inode's ->i_verity_info if not already done. + * + * When combined with fscrypt, this must be called after fscrypt_file_open(). + * Otherwise, we won't have the key set up to decrypt the verity metadata. + * + * Return: 0 on success, -errno on failure + */ +int fsverity_file_open(struct inode *inode, struct file *filp) +{ + if (!IS_VERITY(inode)) + return 0; + + if (filp->f_mode & FMODE_WRITE) { + pr_debug("Denying opening verity file (ino %lu) for write\n", + inode->i_ino); + return -EPERM; + } + + return ensure_verity_info(inode); +} +EXPORT_SYMBOL_GPL(fsverity_file_open); + +/** + * fsverity_prepare_setattr() - prepare to change a verity inode's attributes + * @dentry: dentry through which the inode is being changed + * @attr: attributes to change + * + * Verity files are immutable, so deny truncates. This isn't covered by the + * open-time check because sys_truncate() takes a path, not a file descriptor. + * + * Return: 0 on success, -errno on failure + */ +int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr) +{ + if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) { + pr_debug("Denying truncate of verity file (ino %lu)\n", + d_inode(dentry)->i_ino); + return -EPERM; + } + return 0; +} +EXPORT_SYMBOL_GPL(fsverity_prepare_setattr); + +/** + * fsverity_cleanup_inode() - free the inode's verity info, if present + * + * Filesystems must call this on inode eviction to free ->i_verity_info. + */ +void fsverity_cleanup_inode(struct inode *inode) +{ + fsverity_free_info(inode->i_verity_info); + inode->i_verity_info = NULL; +} +EXPORT_SYMBOL_GPL(fsverity_cleanup_inode); + +int __init fsverity_init_info_cache(void) +{ + fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info, + SLAB_RECLAIM_ACCOUNT, + measurement); + if (!fsverity_info_cachep) + return -ENOMEM; + return 0; +} + +void __init fsverity_exit_info_cache(void) +{ + kmem_cache_destroy(fsverity_info_cachep); + fsverity_info_cachep = NULL; +} |