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Re: Networking Pearl Harbor in the Making

  • From: Robert Bonomi
  • Date: Fri Nov 11 12:05:30 2005

> Date: Fri, 11 Nov 2005 14:15:40 +0000 (GMT)
> From: "Edward B. Dreger" <[email protected]>
> Subject: Re: Networking Pearl Harbor in the Making
> RB> Date: Mon, 7 Nov 2005 14:43:54 -0600 (CST)
> RB> From: Robert Bonomi
> RB> Re-coding to eliminate all 'possible' buffer overflow situations is a *big*
> RB> job.  The required field-length checking for every multi-byte copy/move 
> RB> operation does have a significant negative impact on performance, as well.
> Getting "owned" can also have a significant negative impact on 
> performance.  Of course, maybe the attacker will be benevolent, so 
> perhaps all will be okay...
> Correctness before speed.  Who wants a machine that just gives bad 
> results faster?

"Upgrades" or 'fixes' that cause a machine to run noticably _slower_ than
the 'down-rev' machine are a really good way to alienate customers.  Especially
thosw whose machines are running at nearly 100% capacity before the "upgrade".

If there is a way to render the matter 'harmless' -without- the performance
hit of the 'do it in the theoretically correct manner', *and* that 'defanging'
solution can be delivered in weeks (vs. -years-, for a 'theoretically correct'
approach), there is _clear_benefit_ to taking the 'incorrect' route.  Benefit
that accrues both to the manufacturer _and_ to the CUSTOMERS.

> RB> Merely _identifying_ the 'tainted' (by being in contact -- directly or in-
> RB> directly -- with 'user-supplied' data) data-structures is a task measured
> RB> in man-years.  As is isolating _all_ the points where such tainting occurs.
> Sounds like a pretty good argument for "do it right the first time".

"Irrelevant", when the subject under discussion is pre-existing code that
is _known_ to have (at least one) buffer-overflow problem.  "Do it right 
the first time" is a _really_ difficult target, when the consensus as to
what 'do it right' *means* has changed _since_ the code in question was
first written.  <wry grin>

I'll also quote:
   "In any application, discovered bugs are finite in number,
    UNDISCOVERED BUGS, however, are, by definition _infinite_ in number."

> RB> Then, and only then, can you begin to -plan- how to remove the taint, whether
> RB> by sanity-based bounds-checking, 'clipping' to known limits, explicit length
> RB> checks, or whatever else is appropriate.  
> Hopefully the code is modular.  e.g., running cscope and searching for 
> strcpy(3) invocations is easier than tracking down implemented-in-place 
> equivalents.

*snicker*  _That_ only addresses one small subset of the underlying problem.

strncpy() and/or memcpy() can also corrupt memory -- when the 'length' param
is larger than the receiving field, for example.  This can happen, for example,
when the 'length' is taken 'on faith' from user input, and not validated.