evm: fix security.evm for a file with IMA signature

When both IMA and EVM fix modes are enabled, accessing a file with IMA
signature but missing EVM HMAC won't cause security.evm to be fixed.

Add a function evm_fix_hmac which will be explicitly called to fix EVM
HMAC for this case.

Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Coiby Xu <coxu@redhat.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

2 files changed, 33 insertions, 0 deletions

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index cfc3531cf53f..1b0089b4b796 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -796,6 +796,34 @@ bool evm_revalidate_status(const char *xattr_name)
 }
 
 /**
+ * evm_fix_hmac - Calculate the HMAC and add it to security.evm for fix mode
+ * @dentry: pointer to the affected dentry which doesn't yet have security.evm
+ *          xattr
+ * @xattr_name: pointer to the affected extended attribute name
+ * @xattr_value: pointer to the new extended attribute value
+ * @xattr_value_len: pointer to the new extended attribute value length
+ *
+ * Expects to be called with i_mutex locked.
+ *
+ * Return: 0 on success, -EPERM/-ENOMEM/-EOPNOTSUPP on failure
+ */
+int evm_fix_hmac(struct dentry *dentry, const char *xattr_name,
+		 const char *xattr_value, size_t xattr_value_len)
+
+{
+	if (!evm_fixmode || !evm_revalidate_status((xattr_name)))
+		return -EPERM;
+
+	if (!(evm_initialized & EVM_INIT_HMAC))
+		return -EPERM;
+
+	if (is_unsupported_hmac_fs(dentry))
+		return -EOPNOTSUPP;
+
+	return evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
+}
+
+/**
  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
  * @dentry: pointer to the affected dentry
  * @xattr_name: pointer to the affected extended attribute name
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index ee2e0891febc..0d41d102626a 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -591,6 +591,11 @@ out:
 		     xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
 			if (!ima_fix_xattr(dentry, iint))
 				status = INTEGRITY_PASS;
+		} else if (status == INTEGRITY_NOLABEL) {
+			if (!evm_fix_hmac(dentry, XATTR_NAME_IMA,
+					  (const char *)xattr_value,
+					  xattr_len))
+				status = INTEGRITY_PASS;
 		}
 
 		/*