[PATCH 05/12] ima: Fail rule parsing when buffer hook functions have an invalid action

From: Tyler Hicks <tyhicks@linux.microsoft.com>
To: Mimi Zohar <zohar@linux.ibm.com>,
	Dmitry Kasatkin <dmitry.kasatkin@gmail.com>
Cc: James Morris <jmorris@namei.org>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
	Prakhar Srivastava <prsriva02@gmail.com>,
	linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org,
	linux-security-module@vger.kernel.org
Subject: [PATCH 05/12] ima: Fail rule parsing when buffer hook functions have an invalid action
Date: Mon, 22 Jun 2020 19:32:29 -0500	[thread overview]
Message-ID: <20200623003236.830149-6-tyhicks@linux.microsoft.com> (raw)
In-Reply-To: <20200623003236.830149-1-tyhicks@linux.microsoft.com>

Buffer based hook functions, such as KEXEC_CMDLINE and KEY_CHECK, can
only measure. The process_buffer_measurement() function quietly ignores
all actions except measure so make this behavior clear at the time of
policy load.

The parsing of the keyrings conditional had a check to ensure that it
was only specified with measure actions but the check should be on the
hook function and not the keyrings conditional since
"appraise func=KEY_CHECK" is not a valid rule.

Fixes: b0935123a183 ("IMA: Define a new hook to measure the kexec boot command line arguments")
Fixes: 5808611cccb2 ("IMA: Add KEY_CHECK func to measure keys")
Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
---
 security/integrity/ima/ima_policy.c | 36 +++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index ee5152ecd3d9..ecc234b956a2 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -979,6 +979,39 @@ static void check_template_modsig(const struct ima_template_desc *template)
 #undef MSG
 }
 
+static bool ima_validate_rule(struct ima_rule_entry *entry)
+{
+	if (entry->action == UNKNOWN)
+		return false;
+
+	if (entry->flags & IMA_FUNC) {
+		switch (entry->func) {
+		case NONE:
+		case FILE_CHECK:
+		case MMAP_CHECK:
+		case BPRM_CHECK:
+		case CREDS_CHECK:
+		case POST_SETATTR:
+		case MODULE_CHECK:
+		case FIRMWARE_CHECK:
+		case KEXEC_KERNEL_CHECK:
+		case KEXEC_INITRAMFS_CHECK:
+		case POLICY_CHECK:
+			break;
+		case KEXEC_CMDLINE:
+		case KEY_CHECK:
+			if (entry->action & ~(MEASURE | DONT_MEASURE))
+				return false;
+
+			break;
+		default:
+			return false;
+		}
+	}
+
+	return true;
+}
+
 static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 {
 	struct audit_buffer *ab;
@@ -1156,7 +1189,6 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 			keyrings_len = strlen(args[0].from) + 1;
 
 			if ((entry->keyrings) ||
-			    (entry->action != MEASURE) ||
 			    (entry->func != KEY_CHECK) ||
 			    (keyrings_len < 2)) {
 				result = -EINVAL;
@@ -1362,7 +1394,7 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 			break;
 		}
 	}
-	if (!result && (entry->action == UNKNOWN))
+	if (!result && !ima_validate_rule(entry))
 		result = -EINVAL;
 	else if (entry->action == APPRAISE)
 		temp_ima_appraise |= ima_appraise_flag(entry->func);
-- 
2.25.1

