Re: Strange sfid numbers

Okay, just brushed my mouth after saying some very ugly things when I
saw those FFFFFFF's again.

Anyway, why I send quick mail: you may want to improve your hack
beyond the shadow of doubt by looking for
_FFFFFFFF[8-9A-F] and only _then_ replace the 8 'F's. Why? Because
such a regex (with '_' prefix and [8-9A-F] postcheck) would pick
EXACTLY those units which would have the F's due to some [censored]
sign-bit extension and would prevent the hack from incorrectly being
triggered in the ~ 1:2E9 chance where the actual hash itself produces
a true FFFFFFFF (which would then become FFFFFFFFFFFFFFFF).

Kuddos for that hack anyhow!

Just anal ol' me chiming in, while I shortly take a break from banging
my head against the wall working on some large but ever so slightly
corrupted data loads in SQL server. Ren&Stimpy say: Oohhhhh, JOY!




On Sat, Aug 16, 2008 at 5:12 PM, Thomas Spahni <[email protected]> wrote:
> On Fri, 15 Aug 2008, Paolo wrote:
>
>> On Fri, Aug 15, 2008 at 03:25:13PM +0200, Thomas Spahni wrote:
>> > While testing my setup (BlameTheSegfault) on 64-bit SuSE-10.2 with Ger's
>> ...
>> > 20080815_120057_566189_FFFFFFFFE5355632
>> > 20080815_120347_761063_FFFFFFFFCD92D59C
>> > 20080815_120624_778819_4ABD55BB
>> ...
>> > Why does it put in these blocks of FFFFFFFF ? I suspect a bug in
>> > maillib.crm.
>>
>> nope, that a 64bit issue - see Gerrit's post/thread on this ML with
>> subject
>>
>>   "Ger-138 on line ..." (circa)
>>
>>   Message-ID: <46BEA27B.5020005-mY+prNg7MjwFYqu4Ip00tEEOCMrvLtNR@public.gmane.org>
>>   Date: Sun, 12 Aug 2007 08:02:35 +0200
>
> Hi
>
> First of all: thanks for the pointer.
>
> I understand this is an issue with the hash function shifting in high bits
> on 64-bit OS'es and I suspect that I should not 'fix' that because it
> could break other things.
>
> However, I need consistent sfid numbers, because they are reused in other
> applications, namely database storage. So what's about this quick and
> (very) dirty hack in maillib.crm?
>
> [BlameTheSegfault maillib.crm lines 466 -]
>
> #
> #      Put some text into the cache;
> #      side effect:
> #      variable :reaver_cacheid: to the filename (no directory)
> #      variable :long_cacheid: is set to the file alone (no directory) name
> #
> :reavercache_store:  (:text:)
> {
>   match [:text_cache:] /./   # Don't store it if no reavercache desired
>   isolate (:system_time: :msg_hash:) //
>   syscall () (:system_time:) /date +%Y%m%d_%H%M%S_%N /
>   match [:system_time:] ( :: :cacheid: ) /([[:graph:]]+)..../
>   hash (:msg_hash:) /:*:text:/
>   # Hack by tsp: added next 4 lines to yank bogus FFFFFFFF
>   {
>        match [:msg_hash:] ( :: :bogus_ffff: ) /(FFFFFFFF)......../
>        alter (:bogus_ffff:) //
>   }
>   isolate (:cacheid:) /:*:cacheid:/
> #       It's unclear if the following increases security at all.
>   isolate (:cacheid:) /:*:cacheid:_:*:msg_hash:/
>   isolate (:long_cacheid:) /:*:text_cache:\/texts\/:*:cacheid:/
>   output [:*:long_cacheid:] /:*:text:/
> }
> return
>
>
> This seems to work for me without breaking other things.
>
> Cheers
> Thomas
>
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-- 
Met vriendelijke groeten / Best regards,

Ger Hobbelt

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