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From:   Eric Snowberg <eric.snowberg@oracle.com>
To:     zohar@linux.ibm.com
Cc:     dmitry.kasatkin@gmail.com, paul@paul-moore.com, jmorris@namei.org,
        serge@hallyn.com, roberto.sassu@huawei.com,
        eric.snowberg@oracle.com, kanth.ghatraju@oracle.com,
        konrad.wilk@oracle.com, linux-kernel@vger.kernel.org,
        linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org
Subject: [PATCH v4] integrity: Always reference the blacklist keyring with appraisal
Date:   Wed, 26 Jul 2023 17:17:25 -0400
Message-Id: <20230726211725.393056-1-eric.snowberg@oracle.com>
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Commit 273df864cf746 ("ima: Check against blacklisted hashes for files with
modsig") introduced an appraise_flag option for referencing the blacklist
keyring.  Any matching binary found on this keyring fails signature
validation. This flag only works with module appended signatures.

An important part of a PKI infrastructure is to have the ability to do
revocation at a later time should a vulnerability be found.  Expand the
revocation flag usage to all appraisal functions. The flag is now
enabled by default. Setting the flag with an IMA policy has been
deprecated. Without a revocation capability like this in place, only
authenticity can be maintained. With this change, integrity can now be
achieved with digital signature based IMA appraisal.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
v4 changes:
  Fixed typo
  Also did some performance testing with this patch. With the associative array
  implementation used within the keyring code, there doesn't seem to be much of a
  difference between doing  an appraisal with an empty blacklist keyring and one
  containing 1500 entries.  At this time it is unknown how many entries a user
  would place in this keyring, but this seemed like a bigger number than most use
  cases.  With the 1500 entries, there were only 7 lookups to get through the
  entire list for a file not contained within it.  For something that was
  on the list, there was an average of 4 lookups and a single string compare.
  Based on this testing, IMHO, there could be a lot more entries added to the
  blacklist keyring without any real performance issues.

v3 changes:
  No longer display appraise_flag=check_blacklist in the policy

v2 changes:
  Update the "case Opt_apprase_flag"
  Removed "appraise_flag=" in the powerpc arch specific policy rules
---
 Documentation/ABI/testing/ima_policy  |  6 +++---
 arch/powerpc/kernel/ima_arch.c        |  8 ++++----
 security/integrity/ima/ima_appraise.c | 12 +++++++-----
 security/integrity/ima/ima_policy.c   | 17 +++++------------
 4 files changed, 19 insertions(+), 24 deletions(-)

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index 49db0ff288e5..c2385183826c 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -57,9 +57,9 @@ Description:
 				stored in security.ima xattr. Requires
 				specifying "digest_type=verity" first.)
 
-			appraise_flag:= [check_blacklist]
-			Currently, blacklist check is only for files signed with appended
-			signature.
+			appraise_flag:= [check_blacklist] (deprecated)
+			Setting the check_blacklist flag is no longer necessary.
+			All appraisal functions set it by default.
 			digest_type:= verity
 			    Require fs-verity's file digest instead of the
 			    regular IMA file hash.
diff --git a/arch/powerpc/kernel/ima_arch.c b/arch/powerpc/kernel/ima_arch.c
index 957abd592075..b7029beed847 100644
--- a/arch/powerpc/kernel/ima_arch.c
+++ b/arch/powerpc/kernel/ima_arch.c
@@ -23,9 +23,9 @@ bool arch_ima_get_secureboot(void)
  * is not enabled.
  */
 static const char *const secure_rules[] = {
-	"appraise func=KEXEC_KERNEL_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
+	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
 #ifndef CONFIG_MODULE_SIG
-	"appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
+	"appraise func=MODULE_CHECK appraise_type=imasig|modsig",
 #endif
 	NULL
 };
@@ -49,9 +49,9 @@ static const char *const trusted_rules[] = {
 static const char *const secure_and_trusted_rules[] = {
 	"measure func=KEXEC_KERNEL_CHECK template=ima-modsig",
 	"measure func=MODULE_CHECK template=ima-modsig",
-	"appraise func=KEXEC_KERNEL_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
+	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig|modsig",
 #ifndef CONFIG_MODULE_SIG
-	"appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig",
+	"appraise func=MODULE_CHECK appraise_type=imasig|modsig",
 #endif
 	NULL
 };
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 491c1aca0b1c..870dde67707b 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -458,11 +458,13 @@ int ima_check_blacklist(struct integrity_iint_cache *iint,
 		ima_get_modsig_digest(modsig, &hash_algo, &digest, &digestsize);
 
 		rc = is_binary_blacklisted(digest, digestsize);
-		if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
-			process_buffer_measurement(&nop_mnt_idmap, NULL, digest, digestsize,
-						   "blacklisted-hash", NONE,
-						   pcr, NULL, false, NULL, 0);
-	}
+	} else if (iint->flags & IMA_DIGSIG_REQUIRED && iint->ima_hash)
+		rc = is_binary_blacklisted(iint->ima_hash->digest, iint->ima_hash->length);
+
+	if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
+		process_buffer_measurement(&nop_mnt_idmap, NULL, digest, digestsize,
+					   "blacklisted-hash", NONE,
+					   pcr, NULL, false, NULL, 0);
 
 	return rc;
 }
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index c9b3bd8f1bb9..69452b79686b 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -1280,7 +1280,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
 				     IMA_FSNAME | IMA_GID | IMA_EGID |
 				     IMA_FGROUP | IMA_DIGSIG_REQUIRED |
 				     IMA_PERMIT_DIRECTIO | IMA_VALIDATE_ALGOS |
-				     IMA_VERITY_REQUIRED))
+				     IMA_CHECK_BLACKLIST | IMA_VERITY_REQUIRED))
 			return false;
 
 		break;
@@ -1355,7 +1355,7 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
 
 	/* Ensure that combinations of flags are compatible with each other */
 	if (entry->flags & IMA_CHECK_BLACKLIST &&
-	    !(entry->flags & IMA_MODSIG_ALLOWED))
+	    !(entry->flags & IMA_DIGSIG_REQUIRED))
 		return false;
 
 	/*
@@ -1803,11 +1803,11 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 				if (entry->flags & IMA_VERITY_REQUIRED)
 					result = -EINVAL;
 				else
-					entry->flags |= IMA_DIGSIG_REQUIRED;
+					entry->flags |= IMA_DIGSIG_REQUIRED | IMA_CHECK_BLACKLIST;
 			} else if (strcmp(args[0].from, "sigv3") == 0) {
 				/* Only fsverity supports sigv3 for now */
 				if (entry->flags & IMA_VERITY_REQUIRED)
-					entry->flags |= IMA_DIGSIG_REQUIRED;
+					entry->flags |= IMA_DIGSIG_REQUIRED | IMA_CHECK_BLACKLIST;
 				else
 					result = -EINVAL;
 			} else if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
@@ -1816,18 +1816,13 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 					result = -EINVAL;
 				else
 					entry->flags |= IMA_DIGSIG_REQUIRED |
-						IMA_MODSIG_ALLOWED;
+						IMA_MODSIG_ALLOWED | IMA_CHECK_BLACKLIST;
 			} else {
 				result = -EINVAL;
 			}
 			break;
 		case Opt_appraise_flag:
 			ima_log_string(ab, "appraise_flag", args[0].from);
-			if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) &&
-			    strstr(args[0].from, "blacklist"))
-				entry->flags |= IMA_CHECK_BLACKLIST;
-			else
-				result = -EINVAL;
 			break;
 		case Opt_appraise_algos:
 			ima_log_string(ab, "appraise_algos", args[0].from);
@@ -2271,8 +2266,6 @@ int ima_policy_show(struct seq_file *m, void *v)
 	}
 	if (entry->flags & IMA_VERITY_REQUIRED)
 		seq_puts(m, "digest_type=verity ");
-	if (entry->flags & IMA_CHECK_BLACKLIST)
-		seq_puts(m, "appraise_flag=check_blacklist ");
 	if (entry->flags & IMA_PERMIT_DIRECTIO)
 		seq_puts(m, "permit_directio ");
 	rcu_read_unlock();
-- 
2.39.3