Messages in this thread | | | Date | Thu, 15 May 2003 08:34:06 -0700 (PDT) | From | Booker Bense <> | Subject | Re: [OpenAFS-devel] Re: [PATCH] PAG support, try #2 |
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On Wed, 14 May 2003, Linus Torvalds wrote:
> > On Wed, 14 May 2003, Russ Allbery wrote: > > > > If a single process is in possession of multiple sets of credentials at > > the same time, how does the file system code in the kernel know which ones > > to use for a given operation with a network file system? > > The file system code will have to make up its own mind about it.
- How? The only way I can see is by trying them all...
> > In particular, it's likely the case that only _one_ credential is valid > for that particular mount anyway. You have to ask yourself: where did > these keys all _come_ from in the first place? And the answer is: usually > the filesystem. The key was used and registered at mount-time (encrypted > filesystem), or by some filesystem-specific key exchange.
- This is definitely not the case with AFS or any other distributed filesystem that I know about. I think the semantics of encrypted filesystems vs. distributed ones are different enough that you are going to have problems supporting both with the same tool. Even if there is a key exchange/auth at mount, you will still require additional per user key information in a multi-user file system.
> > So I expect that for many filesystems there will never be any confusion. > Clearly AFS only expects to have one session PAG, for example (since that > is how the _current_ AFS stuff wants to do it), and that implies that > whenever that session PAG is instantiated, the code that instantiates it > will remove any old stale PAGs. > > But the fact that you'd have AFS with just one set of credentials doesn't > mean that the same process might not want to have another PAG for other > uses. Each use might only fit one way.
- You still don't seem to grok what a PAG is. It's merely a pointer to WHERE to look for credentials, it says nothing about how many or what kind you'll find there. You can change credentials without changing your PAG.
> > And even when you have multiple PAG's for the same entity, this is not a > new situation. In fact, UNIX pretty much since day 1 has had it: what do > you think user/group/other are? They are prioritized credentials. There, > you have two different credentials (well, groups are multiple ones in > themselves), with a prioritation scheme ("user matters more, but if user > doesn't match there is no prioritation in groups _except_ one group entry > is special in that we'll use that for new ID creation"). > > Up to the filesystem to decide what it does with the different > credentials, in other words. Some filesystem may decide to only allow one.
- The question is still "WHICH ONE?" How does it decide? Look at them all? If you've got two valid ones how does it decide?
- I think you're confusing the current implementation of PAG's which is admitted a hack a best with the idea of PAG's. It'd be really nice to have kernel with a sane implementation of setpag/getpag.
_ Booker C. Bense - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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