fs-verity: add the hook for file ->open() (fd2d1acf) · Commits · 戴 / test

fs/verity/Makefile

+2 −1

Original line number	Diff line number	Diff line
		# SPDX-License-Identifier: GPL-2.0

		obj-$(CONFIG_FS_VERITY) += hash_algs.o \
		init.o
		init.o \
		open.o

fs/verity/fsverity_private.h

+52 −2

Original line number	Diff line number	Diff line
		@@ -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 */

fs/verity/init.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}

fs/verity/open.c

0 → 100644

+318 −0

Original line number	Diff line number	Diff line
		// 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 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 (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(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(&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;
		}

include/linux/fsverity.h

0 → 100644

+71 −0

Original line number	Diff line number	Diff line
		/* 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() 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 */

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