ipe: use SHA-256 library API instead of crypto_shash API

audit_policy() 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 <[email protected]>
Signed-off-by: Fan Wu <[email protected]>

Author: ebiggers

security/ipe/Kconfig

@@ -6,6 +6,7 @@
 menuconfig SECURITY_IPE
 	bool "Integrity Policy Enforcement (IPE)"
 	depends on SECURITY && SECURITYFS && AUDIT && AUDITSYSCALL
+	select CRYPTO_LIB_SHA256
 	select PKCS7_MESSAGE_PARSER
 	select SYSTEM_DATA_VERIFICATION
 	select IPE_PROP_DM_VERITY if DM_VERITY

security/ipe/audit.c

@@ -6,7 +6,7 @@
 #include <linux/slab.h>
 #include <linux/audit.h>
 #include <linux/types.h>
-#include <crypto/hash.h>
+#include <crypto/sha2.h>
 
 #include "ipe.h"
 #include "eval.h"
@@ -17,7 +17,7 @@
 
 #define ACTSTR(x) ((x) == IPE_ACTION_ALLOW ? "ALLOW" : "DENY")
 
-#define IPE_AUDIT_HASH_ALG "sha256"
+#define IPE_AUDIT_HASH_ALG "sha256" /* keep in sync with audit_policy() */
 
 #define AUDIT_POLICY_LOAD_FMT "policy_name=\"%s\" policy_version=%hu.%hu.%hu "\
 			      "policy_digest=" IPE_AUDIT_HASH_ALG ":"
@@ -182,37 +182,14 @@ static void audit_policy(struct audit_buffer *ab,
 			 const char *audit_format,
 			 const struct ipe_policy *const p)
 {
-	SHASH_DESC_ON_STACK(desc, tfm);
-	struct crypto_shash *tfm;
-	u8 *digest = NULL;
+	u8 digest[SHA256_DIGEST_SIZE];
 
-	tfm = crypto_alloc_shash(IPE_AUDIT_HASH_ALG, 0, 0);
-	if (IS_ERR(tfm))
-		return;
-
-	desc->tfm = tfm;
-
-	digest = kzalloc(crypto_shash_digestsize(tfm), GFP_KERNEL);
-	if (!digest)
-		goto out;
-
-	if (crypto_shash_init(desc))
-		goto out;
-
-	if (crypto_shash_update(desc, p->pkcs7, p->pkcs7len))
-		goto out;
-
-	if (crypto_shash_final(desc, digest))
-		goto out;
+	sha256(p->pkcs7, p->pkcs7len, digest);
 
 	audit_log_format(ab, audit_format, p->parsed->name,
 			 p->parsed->version.major, p->parsed->version.minor,
 			 p->parsed->version.rev);
-	audit_log_n_hex(ab, digest, crypto_shash_digestsize(tfm));
-
-out:
-	kfree(digest);
-	crypto_free_shash(tfm);
+	audit_log_n_hex(ab, digest, sizeof(digest));
 }
 
 /**