[PATCH v2 1/2] evm: fix security.evm for a file with IMA signature

[Coiby Xu <coxu@redhat.com>]

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>
---
 include/linux/evm.h                   |  8 ++++++++
 security/integrity/evm/evm_main.c     | 28 +++++++++++++++++++++++++++
 security/integrity/ima/ima_appraise.c |  5 +++++
 3 files changed, 41 insertions(+)

diff --git a/include/linux/evm.h b/include/linux/evm.h
index ddece4a6b25d..913f4573b203 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -18,6 +18,8 @@ extern enum integrity_status evm_verifyxattr(struct dentry *dentry,
 					     const char *xattr_name,
 					     void *xattr_value,
 					     size_t xattr_value_len);
+int evm_fix_hmac(struct dentry *dentry, const char *xattr_name,
+		 const char *xattr_value, size_t xattr_value_len);
 int evm_inode_init_security(struct inode *inode, struct inode *dir,
 			    const struct qstr *qstr, struct xattr *xattrs,
 			    int *xattr_count);
@@ -51,6 +53,12 @@ static inline enum integrity_status evm_verifyxattr(struct dentry *dentry,
 {
 	return INTEGRITY_UNKNOWN;
 }
+
+static inline int evm_fix_hmac(struct dentry *dentry, const char *xattr_name,
+			       const char *xattr_value, size_t xattr_value_len)
+{
+	return -EOPNOTSUPP;
+}
 #endif
 
 static inline int evm_inode_init_security(struct inode *inode, struct inode *dir,
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 0add782e73ba..1b3edc6d26e9 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -787,6 +787,34 @@ bool evm_revalidate_status(const char *xattr_name)
 	return true;
 }
 
+/**
+ * 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
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index f435eff4667f..f48ef5ec185e 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -601,6 +601,11 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
 		     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;
 		}
 
 		/*

base-commit: e129e479f2e444eaccd822717d418119d39d3d5c
-- 
2.51.0