evm: audit integrity metadata failures

Before modifying an EVM protected extended attribute or any other
metadata included in the HMAC calculation, the existing 'security.evm'
is verified.  This patch adds calls to integrity_audit_msg() to audit
integrity metadata failures.
Reported-by: NSven Vermeulen <sven.vermeulen@siphos.be>
Signed-off-by: NMimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/evm/evm_main.c

@@ -16,6 +16,7 @@
 
 #include <linux/module.h>
 #include <linux/crypto.h>
+#include <linux/audit.h>
 #include <linux/xattr.h>
 #include <linux/integrity.h>
 #include <linux/evm.h>
@@ -24,6 +25,9 @@
 
 int evm_initialized;
 
+static char *integrity_status_msg[] = {
+	"pass", "fail", "no_label", "no_xattrs", "unknown"
+};
 char *evm_hmac = "hmac(sha1)";
 char *evm_hash = "sha1";
 int evm_hmac_version = CONFIG_EVM_HMAC_VERSION;
@@ -262,9 +266,15 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 		if ((evm_status == INTEGRITY_PASS) ||
 		    (evm_status == INTEGRITY_NOXATTRS))
 			return 0;
-		return -EPERM;
+		goto out;
 	}
 	evm_status = evm_verify_current_integrity(dentry);
+out:
+	if (evm_status != INTEGRITY_PASS)
+		integrity_audit_msg(AUDIT_INTEGRITY_METADATA, dentry->d_inode,
+				    dentry->d_name.name, "appraise_metadata",
+				    integrity_status_msg[evm_status],
+				    -EPERM, 0);
 	return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
 }
 
@@ -357,6 +367,9 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 	if ((evm_status == INTEGRITY_PASS) ||
 	    (evm_status == INTEGRITY_NOXATTRS))
 		return 0;
+	integrity_audit_msg(AUDIT_INTEGRITY_METADATA, dentry->d_inode,
+			    dentry->d_name.name, "appraise_metadata",
+			    integrity_status_msg[evm_status], -EPERM, 0);
 	return -EPERM;
 }