// 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;
}