Re: acls+kerberos (limitation)

[Olga Kornievskaia <aglo@umich.edu>]

On Wed, Dec 18, 2019 at 2:34 PM Chuck Lever <chuck.lever@oracle.com> wrote:
>
>
>
> > On Dec 18, 2019, at 2:31 PM, Olga Kornievskaia <aglo@umich.edu> wrote:
> >
> > On Wed, Dec 18, 2019 at 2:05 PM Trond Myklebust <trondmy@hammerspace.com> wrote:
> >>
> >> On Wed, 2019-12-18 at 12:47 -0500, Olga Kornievskaia wrote:
> >>> Hi folks,
> >>>
> >>> Is this a well know but undocumented fact that you can't set large
> >>> amount of acls (over 4096bytes, ~90acls) while mounted using
> >>> krb5i/krb5p? That if you want to get/set large acls, it must be done
> >>> over auth_sys/krb5?
> >>>
> >>
> >> It's certainly not something that I was aware of. Do you see where that
> >> limitation is coming from?
> >
> > I haven't figure it exactly but gss_unwrap_resp_integ() is failing in
> > if (mic_offset > rcv_buf->len). I'm just not sure who sets up the
> > buffer (or why  rvc_buf->len is (4280) larger than a page can a
> > page-limit might make sense to for me but it's not). So you think it
> > should have been working.
>
> The buffer is set up in the XDR encoder. But pages can be added
> by the transport... I guess rcv_buf->len isn't updated when that
> happens.
>

Here's why the acl+krbi/krb5p is failing.

acl tool first calls into the kernel to find out how large of a buffer
it needs to supply and gets acl size then calls down again then code
in __nfs4_get_acl_uncached() allocates a number of pages (this what
set's the available buffer length later used by the sunrpc code). That
works for non-integrity because in call_decode() the call
rpc_unwrap_resp() doesn't try to calculate the checksum on the buffer
that was just read. However, when its krb5i/krb5p we have truncated
buffer and mic offset that's larger than the existing buffer.

I think something needs to be marked to skip doing gss for the initial
acl query?  I first try providing more space in
__nfs4_get_acl_uncached() for when authflavor=krb5i/krb5p and buflen=0
but no matter what the number is the received acl can be larger than
that thus I don't think that's a good approach.

> --
> Chuck Lever
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