Date:   Sat, 22 Jun 2019 15:28:44 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Victor Hsieh <victorhsieh@...gle.com>,
        Chandan Rajendra <chandan@...ux.vnet.ibm.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v5 07/16] fs-verity: add the hook for file ->open()

On 06/20, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> Add the fsverity_file_open() function, which prepares an fs-verity file
> to be read from.  If not already done, it loads the fs-verity descriptor
> from the filesystem and sets up an fsverity_info structure for the inode
> which describes the Merkle tree and contains the file measurement.  It
> also denies all attempts to open verity files for writing.
> 
> This commit also begins the include/linux/fsverity.h header, which
> declares the interface between fs/verity/ and filesystems.
> 
> Reviewed-by: Theodore Ts'o <tytso@....edu>

Reviewed-by: Jaegeuk Kim <jaegeuk@...nel.org>

> Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> ---
>  fs/verity/Makefile           |   3 +-
>  fs/verity/fsverity_private.h |  54 +++++-
>  fs/verity/init.c             |   6 +
>  fs/verity/open.c             | 319 +++++++++++++++++++++++++++++++++++
>  include/linux/fsverity.h     |  71 ++++++++
>  5 files changed, 450 insertions(+), 3 deletions(-)
>  create mode 100644 fs/verity/open.c
>  create mode 100644 include/linux/fsverity.h
> 
> diff --git a/fs/verity/Makefile b/fs/verity/Makefile
> index 398f3f85fa184b..e6a8951c493a5e 100644
> --- a/fs/verity/Makefile
> +++ b/fs/verity/Makefile
> @@ -1,4 +1,5 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
>  obj-$(CONFIG_FS_VERITY) += hash_algs.o \
> -			   init.o
> +			   init.o \
> +			   open.o
> diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
> index 9697aaebb5dc1f..c79746ff335e14 100644
> --- a/fs/verity/fsverity_private.h
> +++ b/fs/verity/fsverity_private.h
> @@ -15,8 +15,7 @@
>  #define pr_fmt(fmt) "fs-verity: " fmt
>  
>  #include <crypto/sha.h>
> -#include <linux/fs.h>
> -#include <uapi/linux/fsverity.h>
> +#include <linux/fsverity.h>
>  
>  struct ahash_request;
>  
> @@ -59,6 +58,40 @@ struct merkle_tree_params {
>  	u64 level_start[FS_VERITY_MAX_LEVELS];
>  };
>  
> +/**
> + * fsverity_info - cached verity metadata for an inode
> + *
> + * When a verity file is first opened, an instance of this struct is allocated
> + * and stored in ->i_verity_info; it remains until the inode is evicted.  It
> + * caches information about the Merkle tree that's needed to efficiently verify
> + * data read from the file.  It also caches the file measurement.  The Merkle
> + * tree pages themselves are not cached here, but the filesystem may cache them.
> + */
> +struct fsverity_info {
> +	struct merkle_tree_params tree_params;
> +	u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
> +	u8 measurement[FS_VERITY_MAX_DIGEST_SIZE];
> +	const struct inode *inode;
> +};
> +
> +/*
> + * Merkle tree properties.  The file measurement is the hash of this structure.
> + */
> +struct fsverity_descriptor {
> +	__u8 version;		/* must be 1 */
> +	__u8 hash_algorithm;	/* Merkle tree hash algorithm */
> +	__u8 log_blocksize;	/* log2 of size of data and tree blocks */
> +	__u8 salt_size;		/* size of salt in bytes; 0 if none */
> +	__le32 sig_size;	/* reserved, must be 0 */
> +	__le64 data_size;	/* size of file the Merkle tree is built over */
> +	__u8 root_hash[64];	/* Merkle tree root hash */
> +	__u8 salt[32];		/* salt prepended to each hashed block */
> +	__u8 __reserved[144];	/* must be 0's */
> +};
> +
> +/* Arbitrary limit to bound the kmalloc() size.  Can be changed. */
> +#define FS_VERITY_MAX_DESCRIPTOR_SIZE	16384
> +
>  /* hash_algs.c */
>  
>  extern struct fsverity_hash_alg fsverity_hash_algs[];
> @@ -85,4 +118,21 @@ fsverity_msg(const struct inode *inode, const char *level,
>  #define fsverity_err(inode, fmt, ...)		\
>  	fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
>  
> +/* open.c */
> +
> +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_info *fsverity_create_info(const struct inode *inode,
> +					   const void *desc, size_t desc_size);
> +
> +void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
> +
> +void fsverity_free_info(struct fsverity_info *vi);
> +
> +int __init fsverity_init_info_cache(void);
> +
>  #endif /* _FSVERITY_PRIVATE_H */
> diff --git a/fs/verity/init.c b/fs/verity/init.c
> index 40076bbe452a48..fff1fd6343357d 100644
> --- a/fs/verity/init.c
> +++ b/fs/verity/init.c
> @@ -33,8 +33,14 @@ void fsverity_msg(const struct inode *inode, const char *level,
>  
>  static int __init fsverity_init(void)
>  {
> +	int err;
> +
>  	fsverity_check_hash_algs();
>  
> +	err = fsverity_init_info_cache();
> +	if (err)
> +		return err;
> +
>  	pr_debug("Initialized fs-verity\n");
>  	return 0;
>  }
> diff --git a/fs/verity/open.c b/fs/verity/open.c
> new file mode 100644
> index 00000000000000..3a3bb27e23f5e3
> --- /dev/null
> +++ b/fs/verity/open.c
> @@ -0,0 +1,319 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * fs/verity/open.c: 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)
> +{
> +	const 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;
> +	}
> +
> +	/* 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 measurement by hashing the fsverity_descriptor. */
> +static int compute_file_measurement(const struct fsverity_hash_alg *hash_alg,
> +				    const struct fsverity_descriptor *desc,
> +				    u8 *measurement)
> +{
> +	return fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), measurement);
> +}
> +
> +/*
> + * Validate the given fsverity_descriptor and create a new fsverity_info from
> + * it.
> + */
> +struct fsverity_info *fsverity_create_info(const struct inode *inode,
> +					   const void *_desc, size_t desc_size)
> +{
> +	const struct fsverity_descriptor *desc = _desc;
> +	struct fsverity_info *vi;
> +	int err;
> +
> +	if (desc_size < sizeof(*desc)) {
> +		fsverity_err(inode, "Unrecognized descriptor size (%zu)",
> +			     desc_size);
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	if (desc->version != 1) {
> +		fsverity_err(inode, "Unrecognized descriptor version: %u",
> +			     desc->version);
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	if (desc->sig_size ||
> +	    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_measurement(vi->tree_params.hash_alg, desc,
> +				       vi->measurement);
> +	if (err) {
> +		fsverity_err(vi->inode, "Error %d computing file measurement",
> +			     err);
> +		goto out;
> +	}
> +	pr_debug("Computed file measurement: %s:%*phN\n",
> +		 vi->tree_params.hash_alg->name,
> +		 vi->tree_params.digest_size, vi->measurement);
> +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 processes may race to set ->i_verity_info, so use cmpxchg.
> +	 * This pairs with the READ_ONCE() in fsverity_get_info().
> +	 */
> +	if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL)
> +		fsverity_free_info(vi);
> +}
> +
> +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\n",
> +			 inode->i_ino);
> +		return -EPERM;
> +	}
> +
> +	return ensure_verity_info(inode);
> +}
> +EXPORT_SYMBOL_GPL(fsverity_file_open);
> +
> +/**
> + * fsverity_cleanup_inode - free the inode's verity info, if present
> + *
> + * 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,
> +						   measurement);
> +	if (!fsverity_info_cachep)
> +		return -ENOMEM;
> +	return 0;
> +}
> diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
> new file mode 100644
> index 00000000000000..1372c236c8770c
> --- /dev/null
> +++ b/include/linux/fsverity.h
> @@ -0,0 +1,71 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * fs-verity: read-only file-based authenticity protection
> + *
> + * This header declares the interface between the fs/verity/ support layer and
> + * filesystems that support fs-verity.
> + *
> + * Copyright 2019 Google LLC
> + */
> +
> +#ifndef _LINUX_FSVERITY_H
> +#define _LINUX_FSVERITY_H
> +
> +#include <linux/fs.h>
> +#include <uapi/linux/fsverity.h>
> +
> +/* Verity operations for filesystems */
> +struct fsverity_operations {
> +
> +	/**
> +	 * Get the verity descriptor of the given inode.
> +	 *
> +	 * @inode: an inode with the S_VERITY flag set
> +	 * @buf: buffer in which to place the verity descriptor
> +	 * @bufsize: size of @buf, or 0 to retrieve the size only
> +	 *
> +	 * If bufsize == 0, then the size of the verity descriptor is returned.
> +	 * Otherwise the verity descriptor is written to 'buf' and its actual
> +	 * size is returned; -ERANGE is returned if it's too large.  This may be
> +	 * called by multiple processes concurrently on the same inode.
> +	 *
> +	 * Return: the size on success, -errno on failure
> +	 */
> +	int (*get_verity_descriptor)(struct inode *inode, void *buf,
> +				     size_t bufsize);
> +};
> +
> +#ifdef CONFIG_FS_VERITY
> +
> +static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
> +{
> +	/* pairs with the cmpxchg_release() in fsverity_set_info() */
> +	return READ_ONCE(inode->i_verity_info);
> +}
> +
> +/* open.c */
> +
> +extern int fsverity_file_open(struct inode *inode, struct file *filp);
> +extern void fsverity_cleanup_inode(struct inode *inode);
> +
> +#else /* !CONFIG_FS_VERITY */
> +
> +static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
> +{
> +	return NULL;
> +}
> +
> +/* open.c */
> +
> +static inline int fsverity_file_open(struct inode *inode, struct file *filp)
> +{
> +	return IS_VERITY(inode) ? -EOPNOTSUPP : 0;
> +}
> +
> +static inline void fsverity_cleanup_inode(struct inode *inode)
> +{
> +}
> +
> +#endif	/* !CONFIG_FS_VERITY */
> +
> +#endif	/* _LINUX_FSVERITY_H */
> -- 
> 2.22.0.410.gd8fdbe21b5-goog

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