[PATCH v3 8/8] ima: Use ima_hash_algo for collision detection in the measurement list

[Roberto Sassu]

Before calculating a digest for each PCR bank, collisions were detected
with a SHA1 digest. This patch includes ima_hash_algo among the algorithms
used to calculate the template digest and checks collisions on that digest.

The position in the measurement entry array of the template digest
calculated with the default IMA algorithm is stored in the
ima_hash_algo_idx global variable and is determined at IMA initialization
time.

Changelog

v2:
- add __ro_after_init to declaration of ima_hash_algo_idx (suggested by
  Mimi)
- replace ima_num_template_digests with
  NR_BANKS(ima_tpm_chip) + ima_extra_slots(suggested by Mimi)
- use ima_hash_algo_idx to access ima_algo_array elements in
  ima_init_crypto()

v1:
- increment ima_num_template_digests before kcalloc() (suggested by Mimi)
- check if ima_tpm_chip is NULL

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
 security/integrity/ima/ima.h        |  1 +
 security/integrity/ima/ima_crypto.c | 19 ++++++++++++++++++-
 security/integrity/ima/ima_queue.c  |  8 ++++----
 3 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index f04bec2ab83f..15663711d0ec 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -53,6 +53,7 @@ extern int ima_policy_flag;
 /* set during initialization */
 extern int ima_hash_algo;
 extern int ima_sha1_idx __ro_after_init;
+extern int ima_hash_algo_idx __ro_after_init;
 extern int ima_extra_slots __ro_after_init;
 extern int ima_appraise;
 extern struct tpm_chip *ima_tpm_chip;
diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index 5ebe31576f7b..84e2b239d31c 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -65,6 +65,7 @@ struct ima_algo_desc {
 };
 
 int ima_sha1_idx __ro_after_init;
+int ima_hash_algo_idx __ro_after_init;
 /* Additional number of slots in ima_algo_array for SHA1 and default IMA algo */
 int ima_extra_slots __ro_after_init;
 
@@ -121,15 +122,25 @@ int __init ima_init_crypto(void)
 		return rc;
 
 	ima_sha1_idx = -1;
+	ima_hash_algo_idx = -1;
 
 	for (i = 0; i < NR_BANKS(ima_tpm_chip); i++) {
 		algo = ima_tpm_chip->allocated_banks[i].crypto_id;
 		if (algo == HASH_ALGO_SHA1)
 			ima_sha1_idx = i;
+
+		if (algo == ima_hash_algo)
+			ima_hash_algo_idx = i;
 	}
 
-	if (ima_sha1_idx < 0)
+	if (ima_sha1_idx < 0) {
 		ima_sha1_idx = NR_BANKS(ima_tpm_chip) + ima_extra_slots++;
+		if (ima_hash_algo == HASH_ALGO_SHA1)
+			ima_hash_algo_idx = ima_sha1_idx;
+	}
+
+	if (ima_hash_algo_idx < 0)
+		ima_hash_algo_idx = NR_BANKS(ima_tpm_chip) + ima_extra_slots++;
 
 	ima_algo_array = kcalloc(NR_BANKS(ima_tpm_chip) + ima_extra_slots,
 				 sizeof(*ima_algo_array), GFP_KERNEL);
@@ -178,6 +189,12 @@ int __init ima_init_crypto(void)
 		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;
 out_array:
 	for (i = 0; i < NR_BANKS(ima_tpm_chip) + ima_extra_slots; i++) {
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 7f7509774b85..58983d0f0214 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -57,8 +57,8 @@ static struct ima_queue_entry *ima_lookup_digest_entry(u8 *digest_value,
 	key = ima_hash_key(digest_value);
 	rcu_read_lock();
 	hlist_for_each_entry_rcu(qe, &ima_htable.queue[key], hnext) {
-		rc = memcmp(qe->entry->digests[ima_sha1_idx].digest,
-			    digest_value, TPM_DIGEST_SIZE);
+		rc = memcmp(qe->entry->digests[ima_hash_algo_idx].digest,
+			    digest_value, hash_digest_size[ima_hash_algo]);
 		if ((rc == 0) && (qe->entry->pcr == pcr)) {
 			ret = qe;
 			break;
@@ -110,7 +110,7 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
 
 	atomic_long_inc(&ima_htable.len);
 	if (update_htable) {
-		key = ima_hash_key(entry->digests[ima_sha1_idx].digest);
+		key = ima_hash_key(entry->digests[ima_hash_algo_idx].digest);
 		hlist_add_head_rcu(&qe->hnext, &ima_htable.queue[key]);
 	}
 
@@ -162,7 +162,7 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
 			   const char *op, struct inode *inode,
 			   const unsigned char *filename)
 {
-	u8 *digest = entry->digests[ima_sha1_idx].digest;
+	u8 *digest = entry->digests[ima_hash_algo_idx].digest;
 	struct tpm_digest *digests_arg = entry->digests;
 	const char *audit_cause = "hash_added";
 	char tpm_audit_cause[AUDIT_CAUSE_LEN_MAX];
-- 
2.17.1