evm: Store and detect metadata inode attributes changes

On stacked filesystem the metadata inode may be different than the one
file data inode and therefore changes to it need to be detected
independently. Therefore, store the i_version, device number, and inode
number associated with the file metadata inode.

Implement a function to detect changes to the inode and if a change is
detected reset the evm_status. This function will be called by IMA when
IMA detects that the metadata inode is different from the file's inode.

Co-developed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

4 files changed, 57 insertions, 10 deletions

diff --git a/include/linux/evm.h b/include/linux/evm.h
index d48d6da32315..ddece4a6b25d 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -26,6 +26,8 @@ extern int evm_protected_xattr_if_enabled(const char *req_xattr_name);
 extern int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
 				     int buffer_size, char type,
 				     bool canonical_fmt);
+extern bool evm_metadata_changed(struct inode *inode,
+				 struct inode *metadata_inode);
 #ifdef CONFIG_FS_POSIX_ACL
 extern int posix_xattr_acl(const char *xattrname);
 #else
@@ -76,5 +78,11 @@ static inline int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
 	return -EOPNOTSUPP;
 }
 
+static inline bool evm_metadata_changed(struct inode *inode,
+					struct inode *metadata_inode)
+{
+	return false;
+}
+
 #endif /* CONFIG_EVM */
 #endif /* LINUX_EVM_H */
diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
index 72e3341ae6f7..51aba5a54275 100644
--- a/security/integrity/evm/evm.h
+++ b/security/integrity/evm/evm.h
@@ -39,6 +39,7 @@ struct xattr_list {
 struct evm_iint_cache {
 	unsigned long flags;
 	enum integrity_status evm_status:4;
+	struct integrity_inode_attributes metadata_inode;
 };
 
 extern struct lsm_blob_sizes evm_blob_sizes;
@@ -74,11 +75,12 @@ int evm_update_evmxattr(struct dentry *dentry,
 			size_t req_xattr_value_len);
 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 		  const char *req_xattr_value,
-		  size_t req_xattr_value_len, struct evm_digest *data);
+		  size_t req_xattr_value_len, struct evm_digest *data,
+		  struct evm_iint_cache *iint);
 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 		  const char *req_xattr_value,
 		  size_t req_xattr_value_len, char type,
-		  struct evm_digest *data);
+		  struct evm_digest *data, struct evm_iint_cache *iint);
 int evm_init_hmac(struct inode *inode, const struct xattr *xattrs,
 		  char *hmac_val);
 int evm_init_secfs(void);
diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 35416f55391c..7c06ffd633d2 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -221,7 +221,8 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
 				 const char *req_xattr_name,
 				 const char *req_xattr_value,
 				 size_t req_xattr_value_len,
-				 uint8_t type, struct evm_digest *data)
+				 uint8_t type, struct evm_digest *data,
+				 struct evm_iint_cache *iint)
 {
 	struct inode *inode = d_inode(d_real(dentry, D_REAL_METADATA));
 	struct xattr_list *xattr;
@@ -231,6 +232,7 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
 	int error;
 	int size, user_space_size;
 	bool ima_present = false;
+	u64 i_version = 0;
 
 	if (!(inode->i_opflags & IOP_XATTR) ||
 	    inode->i_sb->s_user_ns != &init_user_ns)
@@ -294,6 +296,13 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
 	}
 	hmac_add_misc(desc, inode, type, data->digest);
 
+	if (inode != d_backing_inode(dentry) && iint) {
+		if (IS_I_VERSION(inode))
+			i_version = inode_query_iversion(inode);
+		integrity_inode_attrs_store(&iint->metadata_inode, i_version,
+					    inode);
+	}
+
 	/* Portable EVM signatures must include an IMA hash */
 	if (type == EVM_XATTR_PORTABLE_DIGSIG && !ima_present)
 		error = -EPERM;
@@ -305,18 +314,19 @@ out:
 
 int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 		  const char *req_xattr_value, size_t req_xattr_value_len,
-		  struct evm_digest *data)
+		  struct evm_digest *data, struct evm_iint_cache *iint)
 {
 	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
-				    req_xattr_value_len, EVM_XATTR_HMAC, data);
+				    req_xattr_value_len, EVM_XATTR_HMAC, data,
+				    iint);
 }
 
 int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
 		  const char *req_xattr_value, size_t req_xattr_value_len,
-		  char type, struct evm_digest *data)
+		  char type, struct evm_digest *data, struct evm_iint_cache *iint)
 {
 	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
-				     req_xattr_value_len, type, data);
+				     req_xattr_value_len, type, data, iint);
 }
 
 static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
@@ -357,6 +367,7 @@ int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 			const char *xattr_value, size_t xattr_value_len)
 {
 	struct inode *inode = d_backing_inode(dentry);
+	struct evm_iint_cache *iint = evm_iint_inode(inode);
 	struct evm_digest data;
 	int rc = 0;
 
@@ -372,7 +383,7 @@ int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 
 	data.hdr.algo = HASH_ALGO_SHA1;
 	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
-			   xattr_value_len, &data);
+			   xattr_value_len, &data, iint);
 	if (rc == 0) {
 		data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
 		rc = __vfs_setxattr_noperm(&nop_mnt_idmap, dentry,
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index c658d2f1494b..c1ca0894cd8a 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -226,7 +226,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 
 		digest.hdr.algo = HASH_ALGO_SHA1;
 		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
-				   xattr_value_len, &digest);
+				   xattr_value_len, &digest, iint);
 		if (rc)
 			break;
 		rc = crypto_memneq(xattr_data->data, digest.digest,
@@ -247,7 +247,8 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 		hdr = (struct signature_v2_hdr *)xattr_data;
 		digest.hdr.algo = hdr->hash_algo;
 		rc = evm_calc_hash(dentry, xattr_name, xattr_value,
-				   xattr_value_len, xattr_data->type, &digest);
+				   xattr_value_len, xattr_data->type, &digest,
+				   iint);
 		if (rc)
 			break;
 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
@@ -734,6 +735,31 @@ static void evm_reset_status(struct inode *inode)
 }
 
 /**
+ * evm_metadata_changed: Detect changes to the metadata
+ * @inode: a file's inode
+ * @metadata_inode: metadata inode
+ *
+ * On a stacked filesystem detect whether the metadata has changed. If this is
+ * the case reset the evm_status associated with the inode that represents the
+ * file.
+ */
+bool evm_metadata_changed(struct inode *inode, struct inode *metadata_inode)
+{
+	struct evm_iint_cache *iint = evm_iint_inode(inode);
+	bool ret = false;
+
+	if (iint) {
+		ret = (!IS_I_VERSION(metadata_inode) ||
+		       integrity_inode_attrs_changed(&iint->metadata_inode,
+						     metadata_inode));
+		if (ret)
+			iint->evm_status = INTEGRITY_UNKNOWN;
+	}
+
+	return ret;
+}
+
+/**
  * evm_revalidate_status - report whether EVM status re-validation is necessary
  * @xattr_name: pointer to the affected extended attribute name
  *