[PATCH 5/7] ima: Introduce appraise_exec_immutable policy

[Roberto Sassu]

This patch modifies the existing "appraise_exec_tcb" policy, by adding the
appraise_type=meta_immutable requirement for executed files. This policy
can be selected by specifying
ima_policy="appraise_exec_tcb|appraise_exec_immutable" in the kernel
command line.

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt | 4 ++++
 security/integrity/ima/ima_policy.c             | 8 +++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 93c5f78905e2..265f7657f59d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1780,6 +1780,10 @@
 			appraised (with imasig requirement) instead of files
 			owned by root.
 
+			The "appraise_exec_immutable" policy requires immutable
+			metadata for executed files, if the "appraise_exec_tcb"
+			policy is selected.
+
 			The "appraise_tmpfs" policy excludes the dont_appraise
 			rule for the tmpfs and ramfs filesystems for the
 			"appraise_tcb" and "appraise_exec_tcb" policies.
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index a45e494e06e8..6249817ebd04 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -243,6 +243,7 @@ __setup("ima_tcb", default_measure_policy_setup);
 static unsigned int ima_measure_skip_flags __initdata;
 static unsigned int ima_appraise_skip_flags __initdata;
 static bool ima_use_appraise_tcb __initdata;
+static bool ima_use_appraise_exec_immutable __initdata;
 static bool ima_use_secure_boot __initdata;
 static bool ima_use_critical_data __initdata;
 static bool ima_fail_unverifiable_sigs __ro_after_init;
@@ -267,7 +268,9 @@ static int __init policy_setup(char *str)
 		else if (strcmp(p, "appraise_exec_tcb") == 0) {
 			ima_use_appraise_tcb = true;
 			ima_appraise_skip_flags |= IMA_SKIP_OPEN;
-		} else if (strcmp(p, "secure_boot") == 0)
+		} else if (strcmp(p, "appraise_exec_immutable") == 0)
+			ima_use_appraise_exec_immutable = true;
+		else if (strcmp(p, "secure_boot") == 0)
 			ima_use_secure_boot = true;
 		else if (strcmp(p, "critical_data") == 0)
 			ima_use_critical_data = true;
@@ -913,6 +916,9 @@ void __init ima_init_policy(void)
 				  IMA_DEFAULT_POLICY, 0);
 	}
 
+	if (ima_use_appraise_exec_immutable)
+		appraise_exec_rules[0].flags |= IMA_META_IMMUTABLE_REQUIRED;
+
 	if (ima_use_critical_data)
 		add_rules(critical_data_rules,
 			  ARRAY_SIZE(critical_data_rules),
-- 
2.26.2