evm: Align evm_inode_init_security() definition with LSM infrastructure

Change the evm_inode_init_security() definition to align with the LSM
infrastructure. Keep the existing behavior of including in the HMAC
calculation only the first xattr provided by LSMs.

Changing the evm_inode_init_security() definition requires passing the
xattr array allocated by security_inode_init_security(), and the number of
xattrs filled by previously invoked LSMs.

Use the newly introduced lsm_get_xattr_slot() to position EVM correctly in
the xattrs array, like a regular LSM, and to increment the number of filled
slots. For now, the LSM infrastructure allocates enough xattrs slots to
store the EVM xattr, without using the reservation mechanism.
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

include/linux/evm.h

@@ -56,9 +56,10 @@ static inline void evm_inode_post_set_acl(struct dentry *dentry,
 {
 	return evm_inode_post_setxattr(dentry, acl_name, NULL, 0);
 }
-extern int evm_inode_init_security(struct inode *inode,
-				   const struct xattr *xattr_array,
-				   struct xattr *evm);
+
+int evm_inode_init_security(struct inode *inode, struct inode *dir,
+			    const struct qstr *qstr, struct xattr *xattrs,
+			    int *xattr_count);
 extern bool evm_revalidate_status(const char *xattr_name);
 extern int evm_protected_xattr_if_enabled(const char *req_xattr_name);
 extern int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
@@ -157,9 +158,10 @@ static inline void evm_inode_post_set_acl(struct dentry *dentry,
 	return;
 }
 
-static inline int evm_inode_init_security(struct inode *inode,
-					  const struct xattr *xattr_array,
-					  struct xattr *evm)
+static inline int evm_inode_init_security(struct inode *inode, struct inode *dir,
+					  const struct qstr *qstr,
+					  struct xattr *xattrs,
+					  int *xattr_count)
 {
 	return 0;
 }

security/integrity/evm/evm_main.c

@@ -21,6 +21,7 @@
 #include <linux/evm.h>
 #include <linux/magic.h>
 #include <linux/posix_acl_xattr.h>
+#include <linux/lsm_hooks.h>
 
 #include <crypto/hash.h>
 #include <crypto/hash_info.h>
@@ -866,23 +867,26 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 /*
  * evm_inode_init_security - initializes security.evm HMAC value
  */
-int evm_inode_init_security(struct inode *inode,
-				 const struct xattr *lsm_xattr,
-				 struct xattr *evm_xattr)
+int evm_inode_init_security(struct inode *inode, struct inode *dir,
+			    const struct qstr *qstr, struct xattr *xattrs,
+			    int *xattr_count)
 {
 	struct evm_xattr *xattr_data;
+	struct xattr *evm_xattr;
 	int rc;
 
-	if (!(evm_initialized & EVM_INIT_HMAC) ||
-	    !evm_protected_xattr(lsm_xattr->name))
+	if (!(evm_initialized & EVM_INIT_HMAC) || !xattrs ||
+	    !evm_protected_xattr(xattrs->name))
 		return 0;
 
+	evm_xattr = lsm_get_xattr_slot(xattrs, xattr_count);
+
 	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
 	if (!xattr_data)
 		return -ENOMEM;
 
 	xattr_data->data.type = EVM_XATTR_HMAC;
-	rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
+	rc = evm_init_hmac(inode, xattrs, xattr_data->digest);
 	if (rc < 0)
 		goto out;
 

security/security.c

@@ -1647,8 +1647,8 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 	if (!xattr_count)
 		goto out;
 
-	ret = evm_inode_init_security(inode, new_xattrs,
-				      &new_xattrs[xattr_count]);
+	ret = evm_inode_init_security(inode, dir, qstr, new_xattrs,
+				      &xattr_count);
 	if (ret)
 		goto out;
 	ret = initxattrs(inode, new_xattrs, fs_data);