// SPDX-License-Identifier: GPL-2.0
/*
 * Opening fs-verity files
 *
 * Copyright 2019 Google LLC
 */

#include "fsverity_private.h"

#include <linux/export.h>
#include <linux/mm.h>
#include <linux/slab.h>

static struct kmem_cache *fsverity_info_cachep;
static struct rhashtable fsverity_info_hash;

static const struct rhashtable_params fsverity_info_hash_params = {
        .key_len                = sizeof_field(struct fsverity_info, inode),
        .key_offset             = offsetof(struct fsverity_info, inode),
        .head_offset            = offsetof(struct fsverity_info, rhash_head),
        .automatic_shrinking    = true,
};

/**
 * 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 blocks_in_level[FS_VERITY_MAX_LEVELS];
        u64 offset;
        int level;

        memset(params, 0, sizeof(*params));

        hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
        if (!hash_alg)
                return -EINVAL;
        params->hash_alg = hash_alg;
        params->digest_size = hash_alg->digest_size;

        if (salt_size) {
                params->hashstate =
                        fsverity_prepare_hash_state(hash_alg, salt, salt_size);
                if (!params->hashstate) {
                        err = -ENOMEM;
                        goto out_err;
                }
        }

        /*
         * fs/verity/ directly assumes that the Merkle tree block size is a
         * power of 2 less than or equal to PAGE_SIZE.  Another restriction
         * arises from the interaction between fs/verity/ and the filesystems
         * themselves: filesystems expect to be able to verify a single
         * filesystem block of data at a time.  Therefore, the Merkle tree block
         * size must also be less than or equal to the filesystem block size.
         *
         * The above are the only hard limitations, so in theory the Merkle tree
         * block size could be as small as twice the digest size.  However,
         * that's not useful, and it would result in some unusually deep and
         * large Merkle trees.  So we currently require that the Merkle tree
         * block size be at least 1024 bytes.  That's small enough to test the
         * sub-page block case on systems with 4K pages, but not too small.
         */
        if (log_blocksize < 10 || log_blocksize > PAGE_SHIFT ||
            log_blocksize > inode->i_blkbits) {
                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;
        params->log_blocks_per_page = PAGE_SHIFT - log_blocksize;
        params->blocks_per_page = 1 << params->log_blocks_per_page;

        if (WARN_ON_ONCE(!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_digestsize = ilog2(params->digest_size);
        params->log_arity = log_blocksize - params->log_digestsize;
        params->hashes_per_block = 1 << params->log_arity;

        /*
         * 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;
        while (blocks > 1) {
                if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
                        fsverity_err(inode, "Too many levels in Merkle tree");
                        err = -EFBIG;
                        goto out_err;
                }
                blocks = (blocks + params->hashes_per_block - 1) >>
                         params->log_arity;
                blocks_in_level[params->num_levels++] = blocks;
        }

        /* Compute the starting block of each level */
        offset = 0;
        for (level = (int)params->num_levels - 1; level >= 0; level--) {
                params->level_start[level] = offset;
                offset += blocks_in_level[level];
        }

        /*
         * With block_size != PAGE_SIZE, an in-memory bitmap will need to be
         * allocated to track the "verified" status of hash blocks.  Don't allow
         * this bitmap to get too large.  For now, limit it to 1 MiB, which
         * limits the file size to about 4.4 TB with SHA-256 and 4K blocks.
         *
         * Together with the fact that the data, and thus also the Merkle tree,
         * cannot have more than ULONG_MAX pages, this implies that hash block
         * indices can always fit in an 'unsigned long'.  But to be safe, we
         * explicitly check for that too.  Note, this is only for hash block
         * indices; data block indices might not fit in an 'unsigned long'.
         */
        if ((params->block_size != PAGE_SIZE && offset > 1 << 23) ||
            offset > ULONG_MAX) {
                fsverity_err(inode, "Too many blocks in Merkle tree");
                err = -EFBIG;
                goto out_err;
        }

        params->tree_size = offset << log_blocksize;
        params->tree_pages = PAGE_ALIGN(params->tree_size) >> PAGE_SHIFT;
        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
 * builtin signature and with the sig_size field set to 0.
 */
static void compute_file_digest(const struct fsverity_hash_alg *hash_alg,
                                struct fsverity_descriptor *desc,
                                u8 *file_digest)
{
        __le32 sig_size = desc->sig_size;

        desc->sig_size = 0;
        fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), file_digest);
        desc->sig_size = sig_size;
}

/*
 * Create a new fsverity_info from the given fsverity_descriptor (with optional
 * appended builtin signature), and check the signature if present.  The
 * fsverity_descriptor must have already undergone basic validation.
 */
struct fsverity_info *fsverity_create_info(struct inode *inode,
                                           struct fsverity_descriptor *desc)
{
        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 fail;
        }

        memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);

        compute_file_digest(vi->tree_params.hash_alg, desc, vi->file_digest);

        err = fsverity_verify_signature(vi, desc->signature,
                                        le32_to_cpu(desc->sig_size));
        if (err)
                goto fail;

        if (vi->tree_params.block_size != PAGE_SIZE) {
                /*
                 * When the Merkle tree block size and page size differ, we use
                 * a bitmap to keep track of which hash blocks have been
                 * verified.  This bitmap must contain one bit per hash block,
                 * including alignment to a page boundary at the end.
                 *
                 * Eventually, to support extremely large files in an efficient
                 * way, it might be necessary to make pages of this bitmap
                 * reclaimable.  But for now, simply allocating the whole bitmap
                 * is a simple solution that works well on the files on which
                 * fsverity is realistically used.  E.g., with SHA-256 and 4K
                 * blocks, a 100MB file only needs a 24-byte bitmap, and the
                 * bitmap for any file under 17GB fits in a 4K page.
                 */
                unsigned long num_bits =
                        vi->tree_params.tree_pages <<
                        vi->tree_params.log_blocks_per_page;

                vi->hash_block_verified = kvcalloc(BITS_TO_LONGS(num_bits),
                                                   sizeof(unsigned long),
                                                   GFP_KERNEL);
                if (!vi->hash_block_verified) {
                        err = -ENOMEM;
                        goto fail;
                }
        }

        return vi;

fail:
        fsverity_free_info(vi);
        return ERR_PTR(err);
}

int fsverity_set_info(struct fsverity_info *vi)
{
        return rhashtable_lookup_insert_fast(&fsverity_info_hash,
                                             &vi->rhash_head,
                                             fsverity_info_hash_params);
}

struct fsverity_info *__fsverity_get_info(const struct inode *inode)
{
        return rhashtable_lookup_fast(&fsverity_info_hash, &inode,
                                      fsverity_info_hash_params);
}
EXPORT_SYMBOL_GPL(__fsverity_get_info);

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 builtin
 * signature) from the filesystem, and do basic validation of it.
 */
int fsverity_get_descriptor(struct inode *inode,
                            struct fsverity_descriptor **desc_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;
        return 0;
}

static int ensure_verity_info(struct inode *inode)
{
        struct fsverity_info *vi = fsverity_get_info(inode), *found;
        struct fsverity_descriptor *desc;
        int err;

        if (vi)
                return 0;

        err = fsverity_get_descriptor(inode, &desc);
        if (err)
                return err;

        vi = fsverity_create_info(inode, desc);
        if (IS_ERR(vi)) {
                err = PTR_ERR(vi);
                goto out_free_desc;
        }

        /*
         * Multiple tasks may race to set the inode's verity info, in which case
         * we might find an existing fsverity_info in the hash table.
         */
        found = rhashtable_lookup_get_insert_fast(&fsverity_info_hash,
                                                  &vi->rhash_head,
                                                  fsverity_info_hash_params);
        if (found) {
                fsverity_free_info(vi);
                if (IS_ERR(found))
                        err = PTR_ERR(found);
        }

out_free_desc:
        kfree(desc);
        return err;
}

int __fsverity_file_open(struct inode *inode, struct file *filp)
{
        if (filp->f_mode & FMODE_WRITE)
                return -EPERM;
        return ensure_verity_info(inode);
}
EXPORT_SYMBOL_GPL(__fsverity_file_open);

void fsverity_free_info(struct fsverity_info *vi)
{
        kfree(vi->tree_params.hashstate);
        kvfree(vi->hash_block_verified);
        kmem_cache_free(fsverity_info_cachep, vi);
}

void fsverity_remove_info(struct fsverity_info *vi)
{
        rhashtable_remove_fast(&fsverity_info_hash, &vi->rhash_head,
                               fsverity_info_hash_params);
        fsverity_free_info(vi);
}

void fsverity_cleanup_inode(struct inode *inode)
{
        struct fsverity_info *vi = fsverity_get_info(inode);

        if (vi)
                fsverity_remove_info(vi);
}

void __init fsverity_init_info_cache(void)
{
        if (rhashtable_init(&fsverity_info_hash, &fsverity_info_hash_params))
                panic("failed to initialize fsverity hash\n");
        fsverity_info_cachep = KMEM_CACHE_USERCOPY(
                                        fsverity_info,
                                        SLAB_RECLAIM_ACCOUNT | SLAB_PANIC,
                                        file_digest);
}