Zeroize SFTP file payload buffers before freeing

Author: yosuke-wolfssl

src/wolfsftp.c

@@ -793,12 +793,13 @@ static int wolfSSH_SFTP_buffer_read(WOLFSSH* ssh, WS_SFTP_BUFFER* buffer,
 static void wolfSSH_SFTP_buffer_free(WOLFSSH* ssh, WS_SFTP_BUFFER* buffer)
 {
     if (ssh != NULL && buffer != NULL) {
-        buffer->idx = 0;
-        buffer->sz  = 0;
         if (buffer->data != NULL) {
+            ForceZero(buffer->data, buffer->sz);
             WFREE(buffer->data, ssh->ctx->heap, DYNTYPE_BUFFER);
             buffer->data = NULL;
         }
+        buffer->idx = 0;
+        buffer->sz  = 0;
     }
 }
 
@@ -1424,6 +1425,7 @@ static void wolfSSH_SFTP_RecvSetSend(WOLFSSH* ssh, byte* buf, int sz)
 
     /* free up existing data if needed */
     if (buf != state->buffer.data && state->buffer.data != NULL) {
+        ForceZero(state->buffer.data, state->buffer.sz);
         WFREE(state->buffer.data, ssh->ctx->heap, DYNTYPE_BUFFER);
         state->buffer.data = NULL;
     }