fs/verity/hash_algs.c

Source file repositories/reference/linux-study-clean/fs/verity/hash_algs.c

File Facts

System
Linux kernel
Corpus path
fs/verity/hash_algs.c
Extension
.c
Size
5289 bytes
Lines
189
Domain
Core OS
Bucket
VFS And Filesystem Core
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0
/*
 * fs-verity hash algorithms
 *
 * Copyright 2019 Google LLC
 */

#include "fsverity_private.h"

/* The hash algorithms supported by fs-verity */
const struct fsverity_hash_alg fsverity_hash_algs[] = {
	[FS_VERITY_HASH_ALG_SHA256] = {
		.name = "sha256",
		.digest_size = SHA256_DIGEST_SIZE,
		.block_size = SHA256_BLOCK_SIZE,
		.algo_id = HASH_ALGO_SHA256,
	},
	[FS_VERITY_HASH_ALG_SHA512] = {
		.name = "sha512",
		.digest_size = SHA512_DIGEST_SIZE,
		.block_size = SHA512_BLOCK_SIZE,
		.algo_id = HASH_ALGO_SHA512,
	},
};

/**
 * fsverity_get_hash_alg() - get a hash algorithm by number
 * @inode: optional inode for logging purposes
 * @num: the hash algorithm number
 *
 * Get the struct fsverity_hash_alg for the given hash algorithm number.
 *
 * Return: pointer to the hash alg if it's known, otherwise NULL.
 */
const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
						      unsigned int num)
{
	if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
	    !fsverity_hash_algs[num].name) {
		fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
		return NULL;
	}
	return &fsverity_hash_algs[num];
}

/**
 * fsverity_prepare_hash_state() - precompute the initial hash state
 * @alg: hash algorithm
 * @salt: a salt which is to be prepended to all data to be hashed
 * @salt_size: salt size in bytes
 *
 * Return: the kmalloc()'ed initial hash state, or NULL if out of memory.
 */
union fsverity_hash_ctx *
fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
			    const u8 *salt, size_t salt_size)
{
	u8 *padded_salt = NULL;
	size_t padded_salt_size;
	union fsverity_hash_ctx ctx;
	void *res = NULL;

	/*
	 * Zero-pad the salt to the next multiple of the input size of the hash
	 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
	 * bytes for SHA-512.  This ensures that the hash algorithm won't have
	 * any bytes buffered internally after processing the salt, thus making
	 * salted hashing just as fast as unsalted hashing.
	 */
	padded_salt_size = round_up(salt_size, alg->block_size);
	padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
	if (!padded_salt)
		return NULL;
	memcpy(padded_salt, salt, salt_size);

	switch (alg->algo_id) {
	case HASH_ALGO_SHA256:
		sha256_init(&ctx.sha256);
		sha256_update(&ctx.sha256, padded_salt, padded_salt_size);
		res = kmemdup(&ctx.sha256, sizeof(ctx.sha256), GFP_KERNEL);
		break;
	case HASH_ALGO_SHA512:
		sha512_init(&ctx.sha512);
		sha512_update(&ctx.sha512, padded_salt, padded_salt_size);
		res = kmemdup(&ctx.sha512, sizeof(ctx.sha512), GFP_KERNEL);
		break;
	default:
		WARN_ON_ONCE(1);
	}
	kfree(padded_salt);

Annotation

Implementation Notes