Re: GGF's extensions to GSS in Public Comment

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Nicolas Williams wrote:

>Having addressed your comments on GSS_Store_cred(), I'll now re-iterate
>and expand on the problems with using environment variables in the GGF
>proposal.
>
>The problems with the use of environment variables are:
>
>1.  Environment variables are PLATFORM-SPECIFIC:
>
>     - not all platforms can be expected to have this facility
>     - not all platforms can be expected to have the same semantics it
>
>
>2.  GSS_Export_cred() w/ export-to-env-var CANNOT BE MADE THREAD-SAFE
>
>    Environment variables are generally global to a process, not local
>    to a thread, which means that exporting credentials to env vars is
>    inherently not thread safe, at least not if the variable names
>    intended to be used are the same for every call.
>
>    The GGF text says that putenv(3) on the output env var makes the
>    credentials available.  There can be no more than one current
>    credential store at any given time, so I conclude that that
>    gss_export_cred() with option_req == 1 followed by putenv(3) cannot
>    be made thread-safe.
>
>    This precludes any future evolution, of operating systems that
>    support the GGF gss_export_cred() function, towards having
>    multi-threaded GSS-API acceptors w/ PER-THREAD GSS credential
>    stores.  (Please don't assume that this means something about the
>    future evolution of Solaris.)
>
>
>3.  Environment variables are ill-suited for sharing credentials with
>    AFS, DFS, NFS, CIFS, etc...
>
>    Think of AFS tokens, Secure NFS, etc..., where the kernel must know
>    about the current credential store of a thread or process...
>
>    How can environment variables tell the kernel where those
>    credentials are located?  How can putenv(3) do it?
>
>    putenv(3) doesn't tell the kernel anything.
>
>    Changing putenv(3) to interpret "special" variables and take special
>    action for them to address this problem is simply not acceptable.
>
>    Since many operating systems support features such as AFS, DFS,
>    Secure NFS, CIFS, etc... using GSS-API credentials (or similar[1]),
>    we MUST have a way to make credentials available to the OS kernel
>    (or, perhaps, through IPC to special daemons, such as Solaris'
>    gssd(1M) or Windows' LSA).
>
>    And surely you do not propose that GSS acceptors on AFS/DFS/NFS/CIFS
>    clients do additional platform-specific things to make delegated
>    credentials available to the kernel/gssd/LSA/..., or do you?
>
>    Have you discussed this at all with any implementors of
>    kerberized/GSSified networked filesystem protocols?
>
>
>One gets the impression that the GGF GSS_Export_cred() model is based on
>the existing practice of several Kerberos V implementations of using
>environment variables to address credential stores.
>
>(Doesn't the new Kfw MLSA ccache type pretty much mean that Kfw has a
>single credential store peruser on Windows?  Yes, it can still use
>KRB5CCNAME for other ccache types, but those aren't shared with the
>LSA...)
>
>GSS_Store_cred() does not suffer from any of these problems.
>
>The GSS_Store_cred() proposal does acknowledge that manipulation of the
>caller's view of the "current credential store" is a platform-specific
>matter, though I've also proposed (not in I-D form) a generic interface
>to address this (as well as it can be addressed w/o abstracting user
>impersonation).
>
>The only matter that is definitely platform-specific and cannot be
>addressed by any proposal in this space is the matter of how to switch
>user contexts, on multi-user systems (which most GSS-API acceptors run
>on).
>
>[1]  AFS uses Kerberos IV, though it seems possible to use it with
>     Kerberos V and, in any case, with krb524 it's possible to use
>     GSS-API initiator credentials for the Kerberos V mechanism with
>     AFS.
>
>
>Cheers,
>
>Nico
>  
>

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