[RFC PATCH v1 7/7] ima: make SHA1 non-mandatory

[Nicolai Stange <nstange@xxxxxxx>]

For CONFIG_IMA_COMPAT_FALLBACK_TPM_EXTEND=n, SHA-1 is not a hard
requirement anymore. Make ima_init_crypto() continue on SHA-1
instantiation errors.

Note that the configure ima_hash must still be available. If that
happened to be set to SHA-1 and SHA-1 was missing, then IMA would
still fail to initialize.

Signed-off-by: Nicolai Stange <nstange@xxxxxxx>
---
 security/integrity/ima/ima_crypto.c | 60 ++++++++++++++---------------
 1 file changed, 28 insertions(+), 32 deletions(-)

diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index 118ea15d737b..f68435f2679f 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -147,56 +147,51 @@ int __init ima_init_crypto(void)
 		goto out;
 	}
 
+	ima_algo_array[ima_hash_algo_idx].tfm = ima_shash_tfm;
+	ima_algo_array[ima_hash_algo_idx].algo = ima_hash_algo;
+
+	if (ima_hash_algo != HASH_ALGO_SHA1) {
+		ima_algo_array[ima_sha1_idx].tfm =
+			ima_alloc_tfm(HASH_ALGO_SHA1);
+		if (IS_ERR(ima_algo_array[ima_sha1_idx].tfm)) {
+#if IS_ENABLED(CONFIG_IMA_COMPAT_FALLBACK_TPM_EXTEND)
+			/*
+			 * For backwards compatible fallback PCR
+			 * extension, SHA1 is the fallback for missing
+			 * algos.
+			 */
+			rc = PTR_ERR(ima_algo_array[ima_sha1_idx].tfm);
+			goto out_array;
+#endif
+			ima_algo_array[ima_sha1_idx].tfm = NULL;
+			ima_unsupported_tpm_banks_mask |= BIT(ima_sha1_idx);
+		}
+		ima_algo_array[ima_sha1_idx].algo = HASH_ALGO_SHA1;
+	}
+
 	for (i = 0; i < NR_BANKS(ima_tpm_chip); i++) {
 		algo = ima_tpm_chip->allocated_banks[i].crypto_id;
 		ima_algo_array[i].algo = algo;
 
+		/* Initialized separately above. */
+		if (i == ima_hash_algo_idx || i == ima_sha1_idx)
+			continue;
+
 		/* unknown TPM algorithm */
 		if (algo == HASH_ALGO__LAST) {
 			ima_unsupported_tpm_banks_mask |= BIT(i);
 			continue;
 		}
 
-		if (algo == ima_hash_algo) {
-			ima_algo_array[i].tfm = ima_shash_tfm;
-			continue;
-		}
-
 		ima_algo_array[i].tfm = ima_alloc_tfm(algo);
 		if (IS_ERR(ima_algo_array[i].tfm)) {
-			if (algo == HASH_ALGO_SHA1) {
-				rc = PTR_ERR(ima_algo_array[i].tfm);
-				ima_algo_array[i].tfm = NULL;
-				goto out_array;
-			}
-
 			ima_algo_array[i].tfm = NULL;
 			ima_unsupported_tpm_banks_mask |= BIT(i);
 		}
 	}
 
-	if (ima_sha1_idx >= NR_BANKS(ima_tpm_chip)) {
-		if (ima_hash_algo == HASH_ALGO_SHA1) {
-			ima_algo_array[ima_sha1_idx].tfm = ima_shash_tfm;
-		} else {
-			ima_algo_array[ima_sha1_idx].tfm =
-						ima_alloc_tfm(HASH_ALGO_SHA1);
-			if (IS_ERR(ima_algo_array[ima_sha1_idx].tfm)) {
-				rc = PTR_ERR(ima_algo_array[ima_sha1_idx].tfm);
-				goto out_array;
-			}
-		}
-
-		ima_algo_array[ima_sha1_idx].algo = HASH_ALGO_SHA1;
-	}
-
-	if (ima_hash_algo_idx >= NR_BANKS(ima_tpm_chip) &&
-	    ima_hash_algo_idx != ima_sha1_idx) {
-		ima_algo_array[ima_hash_algo_idx].tfm = ima_shash_tfm;
-		ima_algo_array[ima_hash_algo_idx].algo = ima_hash_algo;
-	}
-
 	return 0;
+#if IS_ENABLED(CONFIG_IMA_COMPAT_FALLBACK_TPM_EXTEND)
 out_array:
 	for (i = 0; i < NR_BANKS(ima_tpm_chip) + ima_extra_slots; i++) {
 		if (!ima_algo_array[i].tfm ||
@@ -206,6 +201,7 @@ int __init ima_init_crypto(void)
 		crypto_free_shash(ima_algo_array[i].tfm);
 	}
 	kfree(ima_algo_array);
+#endif
 out:
 	crypto_free_shash(ima_shash_tfm);
 	return rc;
-- 
2.47.1