On Thu, 2022-09-08 at 20:24 +0000, Chuck Lever III wrote: > [ This question comes up on occasion, so I've added a few interested > parties to the Cc: list ] > > > On Sep 8, 2022, at 8:27 AM, battery dude <jyf007@xxxxxxxxx> wrote: > > > > According to https://access.redhat.com/solutions/2117321 this article, > > I want to ask, how to make NFS support the penetration of Linux > > Capabilities > > That link is access-limited, so I was able to view only the top > few paragraphs of it. Not very open, Red Hat. > > TL;DR: I looked into this while trying to figure out how to enable > IMA on NFS files. It's difficult for many reasons. > > > A few of these reasons include: > > The NFS protocol is a standard, and is implemented on a wide variety > of OS platforms. Each OS implements its own flavor of capabilities. > There's no way to translate amongst the variations to ensure > interoperation. On Linux, capabilities(7) says: > > > No standards govern capabilities, but the Linux capability implementation is based on the withdrawn POSIX.1e draft standard; see ⟨https://archive.org/details/posix_1003.1e-990310⟩;. > > I'm not sure how closely other implementations come to implementing > POSIX.1e, but there are enough differences that interoperability > could be a nightmare. Anything Linux has done differently than > POSIX.1e would be encumbered by GPL, making it nearly impossible to > standardize those differences. (Let alone the possible problems > trying to cite a withdrawn POSIX standard in an Internet RFC!) > > The NFSv4 WG could invent our own capabilities scheme, just as was > done with NFSv4 ACLs. I'm not sure everyone would agree that effort > was 100% successful. > > > Currently, an NFS server bases its access control choices on the > RPC user that makes each request. We'd have to figure out a way to > enable NFS clients and servers to communicate more than just user > identity to enable access control via capabilities. > > When sending an NFS request, a client would have to provide a set > of capabilities to the server so the server can make appropriate > access control choices for that request. > > The server would have to report the updated capset when a client > accesses and executes a file with capabilities, and the server > would have to trust that its clients all respect those capsets > correctly. > > > Because capabilities are security-related, setting and retrieving > capabilities should be done only over networks that ensure > integrity of communication. So, protection via RPC-with-TLS or > RPCSEC GSS with an integrity service ought to be a requirement > both for setting and updating capabilities and for transmitting > any protected file content. We have implementations, but there > is always an option of not deploying this kind of protection > when NFS is actually in use, making capabilities just a bit of > security theater in those cases. > > > Given these enormous challenges, who would be willing to pay for > standardization and implementation? I'm not saying it can't or > shouldn't be done, just that it would be a mighty heavy lift. > But maybe other folks on the Cc: list have ideas that could > make this easier than I believe it to be. > > I'm not disputing anything you wrote above, and I clearly haven't thought through the security implications, but I wonder if we could piggyback this info onto security label support somehow? That already requires a (semi-opaque) per-inode attribute, which is mostly what's required for file capabilities. -- Jeff Layton <jlayton@xxxxxxxxxx>
