[37956] in Kerberos
Re: Which gss calls may block on IO
daemon@ATHENA.MIT.EDU (Simo Sorce)
Fri Apr 14 16:15:20 2017
Message-ID: <1492200891.3662.220.camel@redhat.com>
From: Simo Sorce <simo@redhat.com>
To: Isaac Boukris <iboukris@gmail.com>
Date: Fri, 14 Apr 2017 16:14:51 -0400
In-Reply-To: <CAC-fF8Q6XCG6vpvH_7D6hXv-=1w1yx2zCkSJtkiZrBL47AyS5Q@mail.gmail.com>
Mime-Version: 1.0
Cc: kerberos <kerberos@mit.edu>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Errors-To: kerberos-bounces@mit.edu
On Fri, 2017-04-14 at 22:15 +0300, Isaac Boukris wrote:
> On Fri, Apr 14, 2017 at 6:53 PM, Greg Hudson <ghudson@mit.edu> wrote:
> > On 04/14/2017 08:26 AM, Isaac Boukris wrote:
> >> If I only acquire credentials for krb5 mech, can I assume that
> >> gss_accpet would not block on IO?
> >
> > I think that's true, assuming the keytab and profile and /etc/gss/mech
> > file aren't on a network filesystem. In the future we might have
> > pluggable keytab types, at which time a keytab module might do blocking
> > I/O, but that would be an exotic case.
> >
> >> Is there any information available on which gss calls may block on IO
> >> and which not?
> >
> > I'm not aware of a writeup. From memory: gss_acquire_cred() and
> > gss_init_sec_context() can block on either DNS or AS/TGS operations.
> > The per-message functions shouldn't block. gss_inquire_cred() can be
> > less trivial that it sounds (because it can force a resolution of which
> > ccache to use which would ordinarily be delayed until init_sec_context)
> > but I don't think it does network I/O (unless there's a ccselect plugin
> > module which does so, or $HOME/.k5identity is on a network filesystem).
> > The other inquire functions shouldn't block. The delete/release
> > functions shouldn't block.
>
> Thanks for this information.
> fwiw I also noticed rfc 2743 has the following comment about
> gss_{init,accept} calls only: "this call may block pending network
> interactions".
RFC2743 is generic, and with mechanisms different from krb5
gss_accept_sec_context() can indeed block. For example the NTLMSSP
mechanism on a member server would have to contact the DC on accept() to
be able to perform the challenge-response with the client.
Simo.
--
Simo Sorce
Sr. Principal Software Engineer
Red Hat, Inc
________________________________________________
Kerberos mailing list Kerberos@mit.edu
https://mailman.mit.edu/mailman/listinfo/kerberos
