[PATCH][WIP] Make the Samba AD DC multi-process

Stefan Metzmacher metze at samba.org
Thu Dec 1 11:48:24 UTC 2016

Hi Andrew,

>>>> Attached is a WIP set of patches to make Samba connect to ldb
>>>> faster,
>>>> for the @ATTRIBUTES load, used until we can read the full schema.
>>>> This avoids some O(n^2) behaviour for the 600 attributes in the
>>>> default
>>>> schema, which was taking 5% of the time to run a simple
>>>> ldbsearch.
>>>> Please consider, but don't push until I run the beachmarks.
>>> Attached is some work in progress to do this, and to allow the LDAP
>>> and
>>> NETLOGON server to be multi-process. 
>>> This breaks the RPC protocol by not checking the assoc_group when
>>> we
>>> accept a bind to the NETLOGON rpc server in the AD DC.
>>> It also breaks the current link between the lsarpc services and
>>> netlogon, which currently allow a bind on either pipe to access
>>> these
>>> services. 
>>> I've tried to make that all as generic as possible.
>>> Please comment.  I don't plan to push this without coming back to
>>> the
>>> list. 
>> It will take some time to go through this...
>> One comment on hash_computer_name() now:
>> - what's the point of doing such complex logic
>>   using hmac_sha256?
>> - I'd just use tdb_jenkins_hash()
> We didn't want to have the alternate comment:
>  - 'Why do you use an insecure hash that an attacker could target to
> cause a DoS?'
> The idea was just to make it relatively hard for an unauthenticated
> attacker to deterministically bump a real device from the pool.

I don't understand that, the attacker can just use the same string,
which comes in plaintext over the net. That's much easier to an attacker.
than trying to find a hash collision. You can't prevent the DoS that
may happen for our clients.

The only reason we're using a hash at all is to reduce the DoS against
us, when the anonymous clients request challenges for millions of
computer names.

I also can't see how a "secure" hash algorithm truncated to 14 bits
and be more secure than a non-secure algorithm truncated to 14 bits.

As your motivation is performance improvement we should avoid
very expensive hash calculations, which are designed for security
related topics.

So please let us simplify this and just use tdb_jenkins_hash(),
which seems to fast and collision free enough for our most performance
fileserver workloads.


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