evm: skip replacing EVM signature with HMAC on read-only filesystem

If filesystem is mounted read-only or file is immutable, updating
xattr will fail. This is a usual case during early boot until
filesystem is remount read-write. This patch verifies conditions
to skip unnecessary attempt to calculate HMAC and set xattr.

Changes in v2:
* indention changed according to Lindent (requested by Mimi)

Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 9685af3..b392fe6 100644 (file)
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -162,9 +162,14 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
                                        (const char *)xattr_data, xattr_len,
                                        calc.digest, sizeof(calc.digest));
                if (!rc) {
-                       /* we probably want to replace rsa with hmac here */
-                       evm_update_evmxattr(dentry, xattr_name, xattr_value,
-                                  xattr_value_len);
+                       /* Replace RSA with HMAC if not mounted readonly and
+                        * not immutable
+                        */
+                       if (!IS_RDONLY(dentry->d_inode) &&
+                           !IS_IMMUTABLE(dentry->d_inode))
+                               evm_update_evmxattr(dentry, xattr_name,
+                                                   xattr_value,
+                                                   xattr_value_len);
                }
                break;
        default: