Is there a way to fake file on file sistem or Writ

Question

Ok i wrote and application that use Adobe ActiveX control for displaying PDF files.

Adobe ActiveX control load files only from file system. So i nead to feed a file path to this control.

Problem is that i don't want to store PDF files on file system. Event temporary! I wan't to store my PDF files only in memory, and i want to use Adobe ActiveX control.

So i nead:

1) A way to fake file on a file system. So this control would "think" that there is a file, but would load it from memory

2) A way to create file on file system that would be "visible" to only one application, so my PDF control could load it, and other users won't even see it..

3) Something else

PS: I'm not asking to "finish my home work", i'm just asking - is there a way to do this?

Answer 1

If something needs to be on a file system to pass to another application, you can not hide it/limit it to certain processes. Anything your app can see, anything else at the same privilige level can also see/access. You may be able to lock it but how depends on why you want to protect against.

Remember that the user's PC is theirs, not yours so they have full access to everything on it.

Answer 2

You can create a virtual disk and limit access to it to only specific application. Do to this you would have to write a file system driver or a filesystem filter driver. Both work in kernel mode and are tricky to write and maintain. Our company offers components that let you avoid writing drivers yourself and write business logic in user-mode (we provide drivers in those products).

Your most obvious option is to get rid of Adobe Reader control and use some third-party component that displays PDFs and can load them from memory.

But in general a smart hacker would be able to capture your data unless you have (a) non-standard data format, and/or (b) stream the data from the server dynamically, not keeping the complete data on the computer. These are not bulletproof solutions either, but they make hacker's work much harder.

Answer 3

You can almost do it (means: no you can't, but you can do something that comes close).

Creating a file with FILE_ATTRIBUTE_TEMPORARY does in principle create a file, temporarily. However, as long as there is sufficient buffer cache (which is normally always the case unless your file is tens to hundreds of megabytes), the system will not write to disk. This is not just something that happens accidentially, but the actual specified behaviour of this flag.

Further, specifying 0 as share mode and FILE_FLAG_DELETE_ON_CLOSE will prevent any other process from opening your file for as long as you keep it open, even if someone knows it's there, and the file will "disappear" when you close it. Even if your application crashes, the OS will clean up behind you (if DRM is the reason). If you're in super paranoia mode and worried about the system bluescreening while your file exists, you can additionally schedule a pending move too. This will, in case of a system crash, remove the file during boot.

Lastly, given NTFS, you can create an alternate stream with a random, preferrably unique name (e.g. SHA1 of the document or a UUID) on any file or even directory. Alternate streams on directories are ... a kind of nasty hack, but entirely legal and they work just fine, and don't appear in Explorer. This will not really make your file invisible, but nearly so (in almost every practical aspect, anyway). If you're a good citizen, you will want to use the system temp folder for such a thing, not the program folder or some other place that you shouldn't write to.
Creating an alternate stream is dead easy too, just use the normal file or directory name and append a colon (:) and the name of the stream you want. No extra API needed.

Other than that, it gets kind of hard. You can of course always create something like a ramdisk (would be tough to hide it, though), or try to use one of the stream-from-memory functions to fool an application into reading from a memory buffer on the allegation of a file... but that's not trivial stuff.