// 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
  ",
  		 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)
  ", 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
  ",
  			 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;

  }
  
  /*
   * 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_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
  ",

  		 vi->tree_params.hash_alg->name,

  		 vi->tree_params.digest_size, vi->file_digest);

  
  	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 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);
  }
  
  /* 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
  ",
  			 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)
  ",
  			 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;
  }