[PATCH 2/7] ima: Add meta_immutable appraisal type

[Roberto Sassu]

Currently, IMA supports the appraise_type=imasig option in the policy to
require signed file content or metadata. This patch introduces the new
option appraise_type=meta_immutable to require that file metadata is also
immutable, i.e. it cannot have been produced by the system itself but only
from a vendor whose signing key is trusted by the kernel. Currently, this
requirement can be satisfied only by portable signatures.

The main purpose of this option is to ensure a proper label transition
during binary execution, when the target label depends on the label of the
binary being executed. Without it, an administrator might obtain a
different target label by changing the label of the executable.

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
 Documentation/ABI/testing/ima_policy  |  2 +-
 security/integrity/ima/ima_appraise.c |  9 +++++++++
 security/integrity/ima/ima_policy.c   | 13 ++++++++++---
 security/integrity/integrity.h        |  1 +
 4 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index 070779e8d836..bc6597db7c78 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -42,7 +42,7 @@ Description:
 			fowner:= decimal value
 		  lsm:  are LSM specific
 		  option:
-			appraise_type:= [imasig] [imasig|modsig]
+			appraise_type:= [imasig] [imasig|modsig] [meta_immutable]
 			appraise_flag:= [check_blacklist]
 			Currently, blacklist check is only for files signed with appended
 			signature.
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 45e244fc2ef2..5814b8cbe86c 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -430,6 +430,15 @@ int ima_appraise_measurement(enum ima_hooks func,
 		WARN_ONCE(true, "Unexpected integrity status %d\n", status);
 	}
 
+	if ((iint->flags & IMA_META_IMMUTABLE_REQUIRED) &&
+	    status != INTEGRITY_PASS_IMMUTABLE) {
+		status = INTEGRITY_FAIL;
+		cause = "metadata-modifiable";
+		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode,
+				    filename, op, cause, rc, 0);
+		goto out;
+	}
+
 	if (xattr_value)
 		rc = xattr_verify(func, iint, xattr_value, xattr_len, &status,
 				  &cause);
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 4f8cb155e4fd..33b5133645b3 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -1079,7 +1079,8 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
 		return false;
 
 	if (entry->action != APPRAISE &&
-	    entry->flags & (IMA_DIGSIG_REQUIRED | IMA_MODSIG_ALLOWED | IMA_CHECK_BLACKLIST))
+	    entry->flags & (IMA_DIGSIG_REQUIRED | IMA_MODSIG_ALLOWED |
+			    IMA_CHECK_BLACKLIST | IMA_META_IMMUTABLE_REQUIRED))
 		return false;
 
 	/*
@@ -1109,7 +1110,8 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
 				     IMA_UID | IMA_FOWNER | IMA_FSUUID |
 				     IMA_INMASK | IMA_EUID | IMA_PCR |
 				     IMA_FSNAME | IMA_DIGSIG_REQUIRED |
-				     IMA_PERMIT_DIRECTIO))
+				     IMA_PERMIT_DIRECTIO |
+				     IMA_META_IMMUTABLE_REQUIRED))
 			return false;
 
 		break;
@@ -1121,7 +1123,8 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
 				     IMA_INMASK | IMA_EUID | IMA_PCR |
 				     IMA_FSNAME | IMA_DIGSIG_REQUIRED |
 				     IMA_PERMIT_DIRECTIO | IMA_MODSIG_ALLOWED |
-				     IMA_CHECK_BLACKLIST))
+				     IMA_CHECK_BLACKLIST |
+				     IMA_META_IMMUTABLE_REQUIRED))
 			return false;
 
 		break;
@@ -1495,6 +1498,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 				 strcmp(args[0].from, "imasig|modsig") == 0)
 				entry->flags |= IMA_DIGSIG_REQUIRED |
 						IMA_MODSIG_ALLOWED;
+			else if (strcmp(args[0].from, "meta_immutable") == 0)
+				entry->flags |= IMA_META_IMMUTABLE_REQUIRED;
 			else
 				result = -EINVAL;
 			break;
@@ -1850,6 +1855,8 @@ int ima_policy_show(struct seq_file *m, void *v)
 	}
 	if (entry->flags & IMA_CHECK_BLACKLIST)
 		seq_puts(m, "appraise_flag=check_blacklist ");
+	if (entry->flags & IMA_META_IMMUTABLE_REQUIRED)
+		seq_puts(m, "appraise_type=meta_immutable ");
 	if (entry->flags & IMA_PERMIT_DIRECTIO)
 		seq_puts(m, "permit_directio ");
 	rcu_read_unlock();
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index 547425c20e11..be501a63ae30 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -39,6 +39,7 @@
 #define IMA_FAIL_UNVERIFIABLE_SIGS	0x10000000
 #define IMA_MODSIG_ALLOWED	0x20000000
 #define IMA_CHECK_BLACKLIST	0x40000000
+#define IMA_META_IMMUTABLE_REQUIRED	0x80000000
 
 #define IMA_DO_MASK		(IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \
 				 IMA_HASH | IMA_APPRAISE_SUBMASK)
-- 
2.26.2