[PATCH] apparmor: use SHA-256 library API instead of crypto_shash API

Eric Biggers
2025-04-28T19:04:57Z

From: Eric Biggers <ebiggers@google.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@google.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
--
2.49.0