Size of outer volume seen by the OS when the protection on the inner volume is activated

[Veronica Pumberger]

Wouldn't it be possible to provide to the OS the area dedicated to the outer volume when the inner volume protection is activated (for sure, without the inner protection activated, the whole volume (outer + inner) would be seen by the OS to allow the plausible deniability) ? This would allow to use the outer volume as a regular volume without the risk to corrupt the outer volume as specified in the documentation ?
Is this technically impossible ?
What would be the risks of this behavior ?

[Jertzukka]

You cannot mount the filesystem as different sizes, so it's one or the other. The size of the volume is specified in the metadata, partition tables, file tables. It would be obvious if the filesystem was smaller than the partition size, similarly you can't mount the filesystem to be smaller than its real size and for many filesystems end markers exist that indicate where it is supposed to end.

[Veronica Pumberger]

In fact, I was thinking about the use case of a virtual encrypted disk within a file.
In this case, my guess is that the OS knows the file in which the virtual encrypted disk is.
But when veracrypt opens the embedded virtual encrypted disk, I suppose that it is using an encrypted descriptor to know the size of the virtual encrypted disk. And, in this case, it could handle 2 descriptors of the virtual encrypted disk, one when the password of the innner encrypted disk is provided and one when it is not.
But maybe this is a too specific use case and maybe, as you said, the end markers could be a problem.