Bugs and flaws

[dcrocker at eschertech.com (David Crocker)]

I don't think this analogy between software development and manufacturing holds.
There are no "manufacturing defects" in software construction, unless one counts
a buggy chip (e.g. Pentium FPU or similar) or perhaps a buggy compiler. Software
instructions execute predictably and are not subject to the problems of
defective materials, difficulties in keeping dimensions within a precise
tolerance, or wear and tear.

If some small bolt in my car fails because the bolt met its manufacturer's
specification but was not strong enough to withstand the loads it was subjected
to, that is a low-level design error, not a manufacturing error. Similarly, I
view coding errors as low-level design errors.

David Crocker, Escher Technologies Ltd.
Consultancy, contracting and tools for dependable software development
www.eschertech.com



-----Original Message-----
From: sc-l-bounces at securecoding.org [mailto:sc-l-bounces at securecoding.org] On
Behalf Of Chris Wysopal
Sent: 02 February 2006 21:35
To: Gary McGraw
Cc: William Kruse; Wall, Kevin; Secure Coding Mailing List
Subject: RE: [SC-L] Bugs and flaws



In the manufacturing world, which is far more mature than the software
development world, they use the terminology of "design defect" and
"manufacturing defect".  So this distinction is useful and has stood the test of
time.

Flaw and defect are synonymous. We should just pick one. You could say that the
term for manufacturing software is "implementation".

So why do we need to change the terms for the software world?  Wouldn't "design
defect" and "implementation defect" be clearer and more in line with the
manufacturing quality discipline, which the software quality discipline should
be working towards emulating. (When do we get to Six
Sigma?)

I just don't see the usefulness of calling a "design defect" a "flaw". "Flaw" by
itself is overloaded.  And in the software world, "bug" can mean an
implementation or design problem, so "bug" alone is overloaded for describing an
implementation defect.

At @stake the Application Center of Excellence used the terminology "design
flaw" and "implementation flaw".  It well understood by our customers.

As Crispin said in an earlier post on the subject, the line is sometimes blurry.
I am sure this is the case in manufacturing too.  Architecture flaws can be
folded into the design flaw category for simplicity.

My vote is for a less overloaded and clearer terminology.

-Chris

P.S. My father managed a non-destructive test lab at a jet engine manufacturer.
They had about the highest quality requirements in the world. So for many hours
I was regaled with tales about the benefits of performing static analysis on
individual components early in the manufacturing cycle.

They would dip cast parts in a fluorescent liquid and look at them under
ultraviolet light to illuminate cracks caused during casting process. For
critical parts which would receive more stress, such as the fan blades, they
would x-ray each part to inspect for internal cracks. A more expensive process
but warranted due to the increased risk of total system failure for a defect in
those parts.

The static testing was obviously much cheaper and delivered better quality than
just bolting the parts together and doing dynamic testing in a test cell.  It's
a wonder that it has taken the software security world so long to catch onto the
benefits of static testing of implementation.  I think we can learn a lot more
from the manufacturing world.

On Thu, 2 Feb 2006, Gary McGraw wrote:

> Hi all,
>
> When I introduced the "bugs" and "flaws" nomenclature into the 
> literature, I did so in an article about the software security 
> workshop I chaired in 2003 (see http://www.cigital.com/ssw/).  This 
> was ultimately written up in an "On the Horizon" paper published by 
> IEEE Security & Privacy.
>
> Nancy Mead and I queried the SWEBOK and looked around to see if the 
> new usage caused collision.  It did not.  The reason I think it is 
> important to distinguish the two ends of the rather slippery range 
> (crispy is right about that) is that software security as a field is 
> not paying enough attention to architecture.  By identifying flaws as 
> a subcategory of defects (according the the SWEBOK), we can focus some 
> attention on the problem.
>
> > > From the small glossary in "Software Security" (my new book out
> tomorrow):
>
> Bug-A bug is an implementation-level software problem. Bugs may exist 
> in code but never be executed. Though the term bug is applied quite 
> generally by many software practitioners, I reserve use of the term to 
> encompass fairly
> simple implementation errors. Bugs are implementation-level problems
> that
> can be easily discovered and remedied. See Chapter 1.
>
> Flaw-A design-level or architectural software defect. High-level 
> defects cause 50% of software security problems. See Chapter 1.
>
> In any case, I intend to still use these terms like this, and I would 
> be very pleased if you would all join me.
>
> gem
>
>
>
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