Elizabeth Figura zfigura@codeweavers.com writes:
On Wednesday, 24 January 2024 15:26:15 CST Andy Lutomirski wrote:
On Tue, Jan 23, 2024 at 4:59 PM Elizabeth Figura zfigura@codeweavers.com wrote:
ntsync uses a misc device as the simplest and least intrusive uAPI interface.
Each file description on the device represents an isolated NT instance, intended to correspond to a single NT virtual machine.
If I understand this text right, and if I understood the code right, you're saying that each open instance of the device represents an entire universe of NT synchronization objects, and no security or isolation is possible between those objects. For single-process use, this seems fine. But fork() will be a bit odd (although NT doesn't really believe in fork, so maybe this is fine).
Except that NT has *named* semaphores and such. And I'm pretty sure I've written GUI programs that use named synchronization objects (IIRC they were events, and this was a *very* common pattern, regularly discussed in MSDN, usenet, etc) to detect whether another instance of the program is running. And this all works on real Windows because sessions have sufficiently separated namespaces, and the security all works out about as any other security on Windows, etc. But implementing *that* on top of this file-description-plus-integer-equals-object will be fundamentally quite subject to one buggy program completely clobbering someone else's state.
Would it make sense and scale appropriately for an NT synchronization *object* to be a Linux open file description? Then SCM_RIGHTS could pass them around, an RPC server could manage *named* objects, and they'd generally work just like other "Object Manager" objects like, say, files.
It's a sensible concern. I think when I discussed this with Alexandre Julliard (the Wine maintainer, CC'd) the conclusion was this wasn't something we were concerned about.
While the current model *does* allow for processes to arbitrarily mess with each other, accidentally or not, I think we're not concerned with the scope of that than we are about implementing a whole scheduler in user space.
I may have misunderstood something in that dicussion then, because it would definitely be a concern. It's OK for a process to be able to mess up the state of any object that it has an NT handle to, but it shouldn't be possible to mess up the state of unrelated objects in other processes simply by passing the wrong integer id.
The concern is not so much about a malicious process going out of its way to corrupt others, because it could do that through the NT API just as well. But if a wayward pointer corrupts the client-side handle cache, that shouldn't take down the entire session.