Using NSM_REQUEST_MAX_SIZE to initialize buf capacity, added test to …

…ensure there's no panic

src/driver/mod.rs

@@ -40,11 +40,9 @@ struct NsmMessage<'a> {
 
 /// Encode an NSM `Request` value into a vector.
 /// *Argument 1 (input)*: The NSM request.
-/// *Returns*: The vector containing the CBOR encoding.
-fn nsm_encode_request_to_cbor(request: Request) -> Vec<u8> {
-    let mut buf = Vec::with_capacity(512);
-    ciborium::into_writer(&request, &mut buf).unwrap();
-    buf
+/// *Argument 2 (input)*: The buffer that will have the CBOR written into it.
+fn nsm_encode_request_to_cbor(request: Request, buf: &mut Vec<u8>) {
+    ciborium::into_writer(&request, buf).expect("buf's Writer returned an unexpected error");
 }
 
 /// Decode an NSM `Response` value from a raw memory buffer.
@@ -87,7 +85,8 @@ fn nsm_ioctl(fd: i32, message: &mut NsmMessage) -> Option<Errno> {
 /// *Argument 2 (input)*: The NSM request.
 /// *Returns*: The corresponding NSM response from the driver.
 pub fn nsm_process_request(fd: i32, request: Request) -> Response {
-    let cbor_request = nsm_encode_request_to_cbor(request);
+    let mut cbor_request = Vec::with_capacity(NSM_REQUEST_MAX_SIZE);
+    nsm_encode_request_to_cbor(request, &mut cbor_request);
 
     // Check if the request is too large
     if cbor_request.len() > NSM_REQUEST_MAX_SIZE {
@@ -138,3 +137,21 @@ pub fn nsm_exit(fd: i32) {
         Err(e) => error!("File of descriptor {} failed to close: {}", fd, e),
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::{Request, NSM_REQUEST_MAX_SIZE};
+    #[test]
+    fn test_nsm_encode_request_to_cbor_exceed_max_size_without_panic() {
+        let request = Request::ExtendPCR {
+            index: 0,
+            data: vec![0u8; NSM_REQUEST_MAX_SIZE],
+        };
+
+        let mut buf = Vec::with_capacity(NSM_REQUEST_MAX_SIZE);
+        super::nsm_encode_request_to_cbor(request, &mut buf);
+
+        // Ensure the buffer increased its capacity without panicking
+        assert!(buf.len() > NSM_REQUEST_MAX_SIZE);
+    }
+}