linux-kernel - Re: [PATCH] apparmor: use SHA-256 library API instead of crypto

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Message-ID: <ac8fdbfc-02f4-4f35-b8a1-e029b6b322c1@canonical.com>
Date: Sat, 17 May 2025 00:42:14 -0700
From: John Johansen <john.johansen@...onical.com>
To: Eric Biggers <ebiggers@...nel.org>, apparmor@...ts.ubuntu.com
Cc: linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-crypto@...r.kernel.org
Subject: Re: [PATCH] apparmor: use SHA-256 library API instead of crypto_shash
 API

On 4/28/25 12:04, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> This user of SHA-256 does not support any other algorithm, so the
> crypto_shash abstraction provides no value.  Just use the SHA-256
> library API instead, which is much simpler and easier to use.
> 
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Acked-by: John Johansen <john.johansen@...onical.com>

> ---
> 
> This patch is targeting the apparmor tree for 6.16.
> 
>   security/apparmor/Kconfig  |  3 +-
>   security/apparmor/crypto.c | 85 ++++++--------------------------------
>   2 files changed, 13 insertions(+), 75 deletions(-)
> 
> diff --git a/security/apparmor/Kconfig b/security/apparmor/Kconfig
> index 64cc3044a42ce..1e3bd44643dac 100644
> --- a/security/apparmor/Kconfig
> +++ b/security/apparmor/Kconfig
> @@ -57,12 +57,11 @@ config SECURITY_APPARMOR_INTROSPECT_POLICY
>   	  cpu is paramount.
>   
>   config SECURITY_APPARMOR_HASH
>   	bool "Enable introspection of sha256 hashes for loaded profiles"
>   	depends on SECURITY_APPARMOR_INTROSPECT_POLICY
> -	select CRYPTO
> -	select CRYPTO_SHA256
> +	select CRYPTO_LIB_SHA256
>   	default y
>   	help
>   	  This option selects whether introspection of loaded policy
>   	  hashes is available to userspace via the apparmor
>   	  filesystem. This option provides a light weight means of
> diff --git a/security/apparmor/crypto.c b/security/apparmor/crypto.c
> index aad486b2fca65..40e17e153f1e5 100644
> --- a/security/apparmor/crypto.c
> +++ b/security/apparmor/crypto.c
> @@ -9,115 +9,54 @@
>    * Fns to provide a checksum of policy that has been loaded this can be
>    * compared to userspace policy compiles to check loaded policy is what
>    * it should be.
>    */
>   
> -#include <crypto/hash.h>
> +#include <crypto/sha2.h>
>   
>   #include "include/apparmor.h"
>   #include "include/crypto.h"
>   
> -static unsigned int apparmor_hash_size;
> -
> -static struct crypto_shash *apparmor_tfm;
> -
>   unsigned int aa_hash_size(void)
>   {
> -	return apparmor_hash_size;
> +	return SHA256_DIGEST_SIZE;
>   }
>   
>   char *aa_calc_hash(void *data, size_t len)
>   {
> -	SHASH_DESC_ON_STACK(desc, apparmor_tfm);
>   	char *hash;
> -	int error;
> -
> -	if (!apparmor_tfm)
> -		return NULL;
>   
> -	hash = kzalloc(apparmor_hash_size, GFP_KERNEL);
> +	hash = kzalloc(SHA256_DIGEST_SIZE, GFP_KERNEL);
>   	if (!hash)
>   		return ERR_PTR(-ENOMEM);
>   
> -	desc->tfm = apparmor_tfm;
> -
> -	error = crypto_shash_init(desc);
> -	if (error)
> -		goto fail;
> -	error = crypto_shash_update(desc, (u8 *) data, len);
> -	if (error)
> -		goto fail;
> -	error = crypto_shash_final(desc, hash);
> -	if (error)
> -		goto fail;
> -
> +	sha256(data, len, hash);
>   	return hash;
> -
> -fail:
> -	kfree(hash);
> -
> -	return ERR_PTR(error);
>   }
>   
>   int aa_calc_profile_hash(struct aa_profile *profile, u32 version, void *start,
>   			 size_t len)
>   {
> -	SHASH_DESC_ON_STACK(desc, apparmor_tfm);
> -	int error;
> +	struct sha256_state state;
>   	__le32 le32_version = cpu_to_le32(version);
>   
>   	if (!aa_g_hash_policy)
>   		return 0;
>   
> -	if (!apparmor_tfm)
> -		return 0;
> -
> -	profile->hash = kzalloc(apparmor_hash_size, GFP_KERNEL);
> +	profile->hash = kzalloc(SHA256_DIGEST_SIZE, GFP_KERNEL);
>   	if (!profile->hash)
>   		return -ENOMEM;
>   
> -	desc->tfm = apparmor_tfm;
> -
> -	error = crypto_shash_init(desc);
> -	if (error)
> -		goto fail;
> -	error = crypto_shash_update(desc, (u8 *) &le32_version, 4);
> -	if (error)
> -		goto fail;
> -	error = crypto_shash_update(desc, (u8 *) start, len);
> -	if (error)
> -		goto fail;
> -	error = crypto_shash_final(desc, profile->hash);
> -	if (error)
> -		goto fail;
> -
> +	sha256_init(&state);
> +	sha256_update(&state, (u8 *)&le32_version, 4);
> +	sha256_update(&state, (u8 *)start, len);
> +	sha256_final(&state, profile->hash);
>   	return 0;
> -
> -fail:
> -	kfree(profile->hash);
> -	profile->hash = NULL;
> -
> -	return error;
>   }
>   
>   static int __init init_profile_hash(void)
>   {
> -	struct crypto_shash *tfm;
> -
> -	if (!apparmor_initialized)
> -		return 0;
> -
> -	tfm = crypto_alloc_shash("sha256", 0, 0);
> -	if (IS_ERR(tfm)) {
> -		int error = PTR_ERR(tfm);
> -		AA_ERROR("failed to setup profile sha256 hashing: %d\n", error);
> -		return error;
> -	}
> -	apparmor_tfm = tfm;
> -	apparmor_hash_size = crypto_shash_digestsize(apparmor_tfm);
> -
> -	aa_info_message("AppArmor sha256 policy hashing enabled");
> -
> +	if (apparmor_initialized)
> +		aa_info_message("AppArmor sha256 policy hashing enabled");
>   	return 0;
>   }
> -
>   late_initcall(init_profile_hash);
> 
> base-commit: 33035b665157558254b3c21c3f049fd728e72368