// 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 = (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;
}