For example, you can pass a program a capability to bind any privileged port, but not a specific one. For this scenario, just passing an fd bound to the port is actually much simpler and safer. For other capabilities, they’re just too coarse.
The fact that capabilities are implicitly inherited also doesn’t sound like a good approach on security. It’s likely like this due to backward compatibility, but I really think that capabilities ought to be passed explicitly, and we should be able to transfer them between processes. In fact, using an fd as a handle for capabilities would probably be a much clearer and explicit approach.
The setuid binaries already existed, and this was a means to making them (much) more secure without API changes.
https://en.wikipedia.org/wiki/Capability-based_security
that you had in AS/400 or the iAPX 432 where a "capability" is a reference to a system object with associated privileges. It is possible to get this into a POSIX-like system
https://en.wikipedia.org/wiki/Capsicum_(Unix)
It reminds me of using a VAX-11/730 with the VMS operating system in high school where there was a long list of privileges a process could have
https://hunter.goatley.com/vax-professional-articles/vax-pro...
and it was a common game to investigate paths such as "if you have privilege A, B, and C you can get SETPRV and take over the machine"
But Linux "capabilities" do not address this. If you have the permission, you have the permission. And can do the action. Even if the reason why you are trying to do the action (needed for A's request) doesn't match the reason that you are able do it (needed to do things for B).
They're closer to apple entitlements, but inherited through through forks rather than being attached to a binary.
Next after that I’d vote for FreeBSD’s capsicum.
The one thing that makes capabilities usable is that they don't need to follow that rule.
If you don't have processes that let your programs get capabilities from any source other than their creation, you are better just adding your program names into your ACLs.
If I grant something root, I know what that means and I'll be very careful. But if I grant something permission X thinking I'm safe, and then it can be used to gain permission Y, or even root, then I can be accidentally exposed.
There is just a much larger surface area to guard against, ensuring that each granular permission can't be so exploited.
With coarse-grained permissions you end up needing proxies, which is nice because you can do whatever you want in terms of business logic, but also very much not nice because you have to write the proxies and the client code to talk to them, and then you have to keep maintaining and extending them.
Either way you have to do audits and static analysis looking for escalation vectors, and that's strictly harder -but not insurmountable- with fine-grained permissions.
So I think fine-grained permissions win.
I've implemented (and I'm trying to get approval to publish a paper on) a cross between RBAC-style and SMACK-style labeled security (where the labels are literal human-readable strings, not MLS-style bitmaps + levels) for application-level authorization, but it's very fast and should work in-kernel too if anyone wanted to make it work there. This system lets you have authorization as fine- or coarse-grained as you want by using many distinct labels (fine-grained) or few labels (coarse-grained) to label the application (or kernel) objects with.
Traditional unix /etc/group style.
The only LSM I have much experience is SELinux, which capabilities directly as SELinux permissions. I imagine most other general purpose LSMs do simmilar.
I could imagine an LSM that implements a policy of allowing capabilties based on UID/GID; although I'm not aware of any current LSMs that do that.
