Sandboxing

Rewritten-docs.md

@@ -759,7 +759,20 @@ Previous description implies that there is gap between detection of last access
 
 #### Sandboxing
 
-@todo: sandboxing, what possibilites are out there (Linux, Windows), what are general and really needed features, mention isolate, what are isolate features
+There are numerous ways how to approach sandboxing on different platforms,
+describing all possible approaches is out of scope of this document. Instead of
+that have a look at some of the features which are certainly needed for ReCodEx
+and propose some particular sandboxes implementations on linux or Windows.
+
+General purpose of sandbox is safely execute software in any form, from scripts to binaries. Various sandboxes differ in how safely are they and what limiting features they have. Ideal situation is that sandbox will have numerous options and corresponding features which will allow administrators to setup environment as they like and which will not allow user programs to somehow damage executing machine in any way possible.
+
+For ReCodEx and its evaluation there is need for at least these features: execution time and memory limitation, disk operations limit, disk accessibility restrictions and network restrictions. All these features if combined and implemented well are giving pretty safe sandbox which can be used for all kinds of users solutions and should be able to restrict and stop any standard way of attacks or errors.
+
+Linux systems have quite extent support of sandboxing in kernel, there were introduced and implemented kernel namespaces and cgroups which combined can limit hardware resources (cpu, memory) and separate executing program into its own namespace (pid, network). These two features comply sandbox requirement for ReCodEx so there were two options, either find existing solution or implement new one. Luckily existing solution was found and its name is **isolate**. Isolate does not use all possible kernel features but only subset which is still enough to be used by ReCodEx.
+
+The opposite situation is in Windows world, there is limited support in its kernel which makes sandboxing a bit trickier. Windows kernel only has ways how to restrict privileges of a process through restriction of internal access tokens. Monitoring of hardware resources is not possible but used resources can be obtained through newly created job objects. But find sandbox which can do all things needed for ReCodEx seems to be impossible. There are numerous sandboxes for Windows but they all are focused on different things in a lot of cases they serves as safe environment for malicious programs, viruses in particular. Or they are designed as a separate filesystem namespace for installing a lot of temporarily used programs. From all these we can mention Sandboxie, Comodo Internet Security, Cuckoo sandbox and many others. None of these is fitted as sandbox solution for ReCodEx. With this being said we can safely state that designing and implementing new general sandbox for Windows is out of scope of this project.
+
+New general sandbox for Windows is out of bussiness but what about more specialized solution used for instance only for C#. CLR as a virtual machine and runtime environment has a pretty good security support for restrictions and separation which is also transfered to C#. This makes it quite easy to implement simple sandbox within C# but suprisingly there cannot be found some well known general purpose implementations. As said in previous paragraph implementing our own solution is out of scope of project there is simple not enough time. But C# sandbox is quite good topic for another project for example semestral project for C# course so it might be written and integrated in future.
 
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