123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361362363364365366367368369370371372373374375376377378379380381382383384385386387388389390391392393394395396397398399400401402403404405406407408 |
- // SPDX-License-Identifier: GPL-2.0
- /*
- * 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)
- {
- 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 = ((u64)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;
- }
- params->level0_blocks = params->level_start[0];
- /* 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 digest by hashing the fsverity_descriptor excluding the
- * signature and with the sig_size field set to 0.
- */
- static int compute_file_digest(struct fsverity_hash_alg *hash_alg,
- struct fsverity_descriptor *desc,
- u8 *file_digest)
- {
- __le32 sig_size = desc->sig_size;
- int err;
- desc->sig_size = 0;
- err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), file_digest);
- desc->sig_size = sig_size;
- return err;
- }
- /*
- * Create a new fsverity_info from the given fsverity_descriptor (with optional
- * appended signature), and check the signature if present. The
- * fsverity_descriptor must have already undergone basic validation.
- */
- struct fsverity_info *fsverity_create_info(const struct inode *inode,
- struct fsverity_descriptor *desc,
- size_t desc_size)
- {
- struct fsverity_info *vi;
- int err;
- 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_digest(vi->tree_params.hash_alg, desc,
- vi->file_digest);
- if (err) {
- fsverity_err(inode, "Error %d computing file digest", err);
- goto out;
- }
- pr_debug("Computed file digest: %s:%*phN\n",
- vi->tree_params.hash_alg->name,
- vi->tree_params.digest_size, vi->file_digest);
- err = fsverity_verify_signature(vi, desc->signature,
- le32_to_cpu(desc->sig_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 tasks may race to set ->i_verity_info, so use
- * cmpxchg_release(). This pairs with the smp_load_acquire() in
- * fsverity_get_info(). I.e., here we publish ->i_verity_info with a
- * RELEASE barrier so that other tasks can ACQUIRE it.
- */
- if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL) {
- /* Lost the race, so free the fsverity_info we allocated. */
- fsverity_free_info(vi);
- /*
- * Afterwards, the caller may access ->i_verity_info directly,
- * so make sure to ACQUIRE the winning fsverity_info.
- */
- (void)fsverity_get_info(inode);
- }
- }
- void fsverity_free_info(struct fsverity_info *vi)
- {
- if (!vi)
- return;
- kfree(vi->tree_params.hashstate);
- kmem_cache_free(fsverity_info_cachep, vi);
- }
- static bool validate_fsverity_descriptor(struct inode *inode,
- const struct fsverity_descriptor *desc,
- size_t desc_size)
- {
- if (desc_size < sizeof(*desc)) {
- fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
- desc_size);
- return false;
- }
- if (desc->version != 1) {
- fsverity_err(inode, "Unrecognized descriptor version: %u",
- desc->version);
- return false;
- }
- if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
- fsverity_err(inode, "Reserved bits set in descriptor");
- return false;
- }
- if (desc->salt_size > sizeof(desc->salt)) {
- fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
- return false;
- }
- 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 false;
- }
- if (le32_to_cpu(desc->sig_size) > desc_size - sizeof(*desc)) {
- fsverity_err(inode, "Signature overflows verity descriptor");
- return false;
- }
- return true;
- }
- /*
- * Read the inode's fsverity_descriptor (with optional appended signature) from
- * the filesystem, and do basic validation of it.
- */
- int fsverity_get_descriptor(struct inode *inode,
- struct fsverity_descriptor **desc_ret,
- size_t *desc_size_ret)
- {
- int res;
- struct fsverity_descriptor *desc;
- 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);
- kfree(desc);
- return res;
- }
- if (!validate_fsverity_descriptor(inode, desc, res)) {
- kfree(desc);
- return -EINVAL;
- }
- *desc_ret = desc;
- *desc_size_ret = res;
- return 0;
- }
- /* 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;
- size_t desc_size;
- int err;
- if (vi)
- return 0;
- err = fsverity_get_descriptor(inode, &desc, &desc_size);
- if (err)
- return err;
- vi = fsverity_create_info(inode, desc, desc_size);
- if (IS_ERR(vi)) {
- err = PTR_ERR(vi);
- goto out_free_desc;
- }
- fsverity_set_info(inode, vi);
- err = 0;
- out_free_desc:
- kfree(desc);
- return err;
- }
- /**
- * 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
- * @inode: an inode being evicted
- *
- * 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,
- file_digest);
- 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;
- }
|