According to this configure file CONFIG_NFSD_V4_SECURITY_LABEL=y is enabled Jeff Layton <jlayton@xxxxxxxxxx> 于2022年9月8日周四 16:28写道： > > On Thu, 2022-09-08 at 21:17 +0000, Chuck Lever III wrote: > > > > > On Sep 8, 2022, at 5:03 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > > > > > 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 No standards govern capabilities, but the Linux capability implementation is based on the withdrawn POSIX.1e draft standard; see ⟨https://archive.org/details/posix_1003.1e-990310⟩;.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 trying to cite a withdrawn POSIX standard in an Internet RFC!)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. > > > > That was the starting idea for accessing IMA metadata on NFS until > > we discovered that NFSv4 security labels are intended to enable only > > a single label per file. Capabilities are often present with SELinux > > labels. > > > > It would work for a proof of concept, though. > > > > Yeah, that why I was saying "piggyback". > > You'd need a combined SELinux+capabilities label (potentially with other > stuff in it as well). When you got one from the server, you'd have to > extract each piece and put in the right places in the inode. > > But, like I said...I haven't thought through the implications here at > all (and am not looking for a project at the moment). ;) > -- > Jeff Layton <jlayton@xxxxxxxxxx>
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