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Re: SMTP-SASL auth failure caching.

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  • Keean Schupke
    This is a resubmission, apparently the patch plus my preamble is over the 40k character limit. The patch is short enough, so it must be all my waffle at the
    Message 1 of 77 , Dec 2, 2007
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      This is a resubmission, apparently the patch plus my preamble is over
      the 40k character limit. The patch is short enough, so it must be all
      my waffle at the beginning! I will post the patch in the next mail.


      Well, this is V2.1 I guess. I went with most of the changes suggested,
      and I modified the interface to cache_client. Now you pass in the
      "service name" and "CLNT_STREAM**", so the cache client is stateless,
      and can be used from many places in the same process at the same time.
      This coupled with the ability to change the serivce name in the
      "master.cf" file, and override the cache file with "-o cache_map"
      allows the cache service to really provide multiple caches to multiple
      services at the same time. For good measure, I added a
      "smtp_sasl_auth_cache_service" conf variable to allow you to set the
      name of the auth_cache service to something else.

      I have tested the patch with both soft_bounce disabled and enabled,
      and all is behaving as required.

      Also, using the little cache_client test program at the end of
      cache_client.c I notice the memory based hash table (dict_ht) does not
      support delete. This should not affect funtionality, as an expired or
      corrupt cache entry will just be ignored, but it does mean warnings
      are generated evey time an attempt is made to delete a cache entry in
      the "volatile" mode. This affects verify.c as well. I assume it is not
      worth disabling the delete call for this mode, just incate dict_ht
      gains this functionality in the future.

      The patch includes adding the service to master.cf (although I run
      pretty much everything in a chroot jail, which I believe is not the
      default... so that one may not apply). Also I haven't made any changes
      to the main.cf, and the patch was generated after the soft_bounce
      patch, and the comments there may be slightly different.

      Regards,
      Keean Schupke, Fry-IT Ltd.

      On 02/12/2007, Wietse Venema <wietse@...> wrote:
      > Victor Duchovni:
      > > On Sat, Dec 01, 2007 at 10:43:53PM +0000, Keean Schupke wrote:
      > >
      > > > have added a dsn_valid() check, and swapped to using strtoul, along
      > > > with unsigned long for all time values... no negative times.
      > >
      > > In http://tools.ietf.org/html/rfc4954#section-6, the enhanced status
      > > code for AUTH failures is defined as:
      > >
      > > 535 5.7.8 Authentication credentials invalid
      > >
      > > which extends:
      > >
      > > http://tools.ietf.org/html/rfc3463#section-3.8
      > >
      > > which only defines 5.7.0-5.7.7
      > >
      > > It may be appropriate to further check the enhanced status code (if
      > > present) and skip responses where 535 is accompanied by an enhanced
      > > status code other than 5.7.8. On the other hand, the 535 response is not
      > > currently supposed to be accompanied by any other enhanced status code,
      > > so this may be too pedantic.
      >
      > As long as Postfix recognizes the 535 SMTP status in this very
      > specific context (AUTH request) there should be no need to require
      > a specific enhanced status code.
      >
      > It is the SMTP client's job to translate protocol-specific server
      > replies (535 5.7.8 yadda yadda) into something meaningful (suspend
      > all further usage of this password for this user and server).
      >
      > Is there a need for the SMTP client to make a sanitized version of
      > the server reply available to other software? If not, then why
      > bother.
      >
      > Wietse
      >
    • Victor Duchovni
      ... Yes, that s the idea. Also CPUs have historically gotten faster year-by-year. Moore s law is looking a bit more feeble lately, we are getting the
      Message 77 of 77 , Dec 4, 2007
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        On Tue, Dec 04, 2007 at 09:04:19PM +0000, Keean Schupke wrote:

        > How about we make the key iterations a config variable, and let the
        > user make the balance between speed and security?

        Yes, that's the idea. Also CPUs have historically gotten faster
        year-by-year. Moore's law is looking a bit more feeble lately, we are
        getting the feature-size scaling (more cores per die) but the clock-rate
        seems to have stalled for a bit.

        Finally, the table will not be in the chroot jail, proxymap/proxywrite
        won't be chrooted even when other processes are. So some "postfix"
        processes will have less access to the table than others.

        Anyway this is all coverging to something sensible. The question for
        the smtp(8) side is whether making the password hash the key is the
        best choice. We could make "nexthop user" the key, and stick the
        password hash in the result. That way deletion will actually work.

        Otherwise, new passwords will be set before the fail map entry expires,
        and the table entry becomes orphaned.

        If this change is made, the entry is valid only if not expired, and the
        password hash matches. Looks a lot an /etc/shadow entry with a user name
        and PKCS#5 v2 password hash, only it perversely records invalid passwords!

        --
        Viktor.

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