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Independent Submission J. Snijders
Request for Comments: 9225 Fastly
Category: Informational C. Morrow
ISSN: 2070-1721 Google
R. van Mook
Asteroid
1 April 2022
Software Defects Considered Harmful
Abstract
This document discourages the practice of introducing software
defects in general and in network protocol implementations
specifically. Software defects are one of the largest cost drivers
for the networking industry. This document is intended to clarify
the best current practice in this regard.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not candidates for any level of Internet Standard;
see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9225.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction
2. Requirements Language
3. Examples of High-Impact Software Defects
4. Best Current Practises
5. Security Considerations
6. IANA Considerations
7. References
7.1. Normative References
7.2. Informative References
Appendix A. Future Research
Acknowledgements
Authors' Addresses
1. Introduction
Software defects (informally known as "bugs") have been the cause and
effect of innumerable system degradations and failures over the
years. Bugs are errors, flaws, or faults in a computer program that
cause the program to produce an incorrect or unexpected result.
(Please note: unexpected results caused by bugs are not a valid
substitute for high-quality random number generators, though high-
quality random number generators are generally not considered to be
bugs.)
Endeavoring to reduce the number of degradations in the future,
implementers MUST NOT introduce bugs when writing software. This
document outlines why bugs are considered harmful and proposes a set
of recommendations.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Examples of High-Impact Software Defects
In June 1996, the European Space Agency [ARIANE] launched an unmanned
rocket -- costing several billion dollars in development -- only to
see it go [KABOOM] 40 seconds after takeoff. A software exception
had occurred during the execution of a data conversion from 64-bit
floating point to 16-bit signed integer value. The floating point
number that was converted had a value greater than what could be
represented by a 16-bit signed integer. The vehicle probably would
not have disintegrated if the defect had not been written into the
software.
As an example of the detrimental effects of bugs in physically hard
to reach systems: the [NASA] Deep Impact spacecraft [DEEPIMPACT] was
rendered inoperable due to a fault in the fault-protection software,
which in turn triggered endless computer reboots. Mission control
was unable to recover the system from this error condition because no
engineers were available on-site. The commute was deemed infeasible
due to a lack of reasonably priced commercial transport options in
that region of the solar system.
In 1983, the Soviet Union's Early Warning Satellite System
[Serpukhov] announced it had detected a possible missile launch
originating in the US; fortunately, a human operator recognized this
as a likely system failure. Indeed, a retrospective analysis
suggested the software had misclassified reflections from cloud cover
as missile launch blooms. With this bug, the software held the
potential to trigger a cascading sequence of events that could've led
to the start of a planetary-scale war. Seemingly innocuous software
defects can have outsized impact, and sometimes it pays off to simply
do nothing and wait.
The US Department of Commerce's National Institute of Standards and
Technology [NIST] commissioned a study to develop a deeper
understanding of the prevalence of software defects and their cost to
society. The study estimated about 0.6 percent of the gross domestic
product is squandered due to programming bugs. Each person works
approximately one hour a week to compensate for this debt -- an hour
that could've been spent in leisure -- in addition to any time spent
on the direct consequences of buggy software.
The universal deployment of IP networks on Avian Carriers [RFC1149]
is facing a multi-decade delay. After operators discovered that
birds are not real (now [confirmed] by the US Government), work began
to first understand the many [quirks] of the drones' firmware before
proceeding with wider-scale deployment. No clear timelines exist at
this point in time.
For more examples, consult the RISKS Digest [RISKS]: it documents a
multitude of examples of defects in technological infrastructure and
their risk to society. Unsupervised study of the Digest archive may
induce a sense of panic.
4. Best Current Practises
1. Authors MUST NOT implement bugs.
2. If bugs are introduced in code, they MUST be clearly documented.
3. When implementing specifications that are broken by design, it is
RECOMMENDED to aggregate multiple smaller bugs into one larger
bug. This will be easier to document: rather than having a lot
of hard-to-track inconsequential bugs, there will be only a few
easy-to-recognise significant bugs.
4. The aphorism "It's not a bug, it's a feature" is considered rude.
5. Assume all external input is the result of (a series of) bugs.
(Especially in machine-to-machine applications such as
implementations of network protocols.)
6. In fact, assume all internal inputs also are the result of bugs.
5. Security Considerations
With the production of fewer bugs, there will necessarily be fewer
security impacts. To improve the collective security posture, a
thorough review of ALL existing software to find any remaining bugs
is RECOMMENDED.
As it is assumed that there is an even distribution of bugs through
all software, it is safe to consider any piece of software to be bug
free once a certain number of bugs have been found.
Some philosophers argue in defense of an obviously wrong contrary
view that bugs introduce a certain amount of unpredictable variance
in behaviour, which in turn could serve to increase security. Such
heretics might even go one step further and celebrate the existence
of bugs, shielding issues from public scrutiny. However, it
[ostensibly] is in society's best interest to fully disclose any and
all bugs as soon as they are discovered.
6. IANA Considerations
IANA is assumed to operate flawlessly.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[ARIANE] Arnold, D. N., "The Explosion of the Ariane 5", August
2000, <https://www-users.cse.umn.edu/~arnold/disasters/
ariane.html>.
[confirmed]
US Consumer Product Safety Commission (@USCPSC), "Birds
are real.", Twitter, 5 January 2022,
<https://twitter.com/USCPSC/status/1478794691634155523>.
[DEEPIMPACT]
Wallace, M., "Subject: Re: [tz] Deep Impact: wrong time
zone?", message to the tz@iana.org mailing list, 23
September 2013, <https://mm.icann.org/pipermail/
tz/2013-September/020357.html>.
[incomplete]
Raatikainen, P., "Gödel's Incompleteness Theorems",
Stanford Encyclopedia of Philosophy, November 2013,
<https://plato.stanford.edu/entries/goedel-
incompleteness/>.
[IRTF] IRTF, "Internet Research Task Force",
<https://www.irtf.org/>.
[KABOOM] Jure, V. A., "Kapow! Zap! Splat! How comics make sound on
the page", The Conversation, 10 June 2021,
<https://theconversation.com/kapow-zap-splat-how-comics-
make-sound-on-the-page-160455>.
[NASA] NASA, "NASA's Deep Space Comet Hunter Mission Comes to an
End", September 2013,
<https://www.nasa.gov/mission_pages/deepimpact/media/
deepimpact20130920.html>.
[NIST] NIST, "Software Errors Cost U.S. Economy $59.5 Billion
Annually", Wayback Machine archive, June 2002,
<https://web.archive.org/web/20090610052743/
http://www.nist.gov/public_affairs/releases/n02-10.htm>.
[ostensibly]
Swire, P., "A Model for When Disclosure Helps Security:
What Is Different About Computer and Network Security?", 3
Journal on Telecommunications and High Technology Law 163,
August 2004, <http://dx.doi.org/10.2139/ssrn.531782>.
[quirks] Stockton, N., "What's Up With That: Birds Bob Their Heads
When They Walk", WIRED, January 2015,
<https://www.wired.com/2015/01/whats-birds-bob-heads-
walk/>.
[RFC1149] Waitzman, D., "Standard for the transmission of IP
datagrams on avian carriers", RFC 1149,
DOI 10.17487/RFC1149, April 1990,
<https://www.rfc-editor.org/info/rfc1149>.
[RISKS] ACM Committee on Computers and Public Policy, "The RISKS
Digest", <https://catless.ncl.ac.uk/Risks/>.
[Serpukhov]
Long, T., "Sept. 26, 1983: The Man Who Saved the World by
Doing ... Nothing", WIRED, September 2007,
<https://www.wired.com/2007/09/dayintech-0926-2/>.
Appendix A. Future Research
The existence of this very document of course begs the question: what
are software defects, truly? Do bugs happen for a purpose? Is what
we perceive as the concept of bugs an indication for a wider issue in
the natural world? Do mistakes happen in other domains? Are they
evidence of a superior software architect?
An interdisciplinary approach to understand mistakes might be an area
of further study for the [IRTF]. It may very well turn out that
mistakes are provably detrimental in all domains; however, the
authors do not feel qualified to make any statements in this regard.
Once made aware of the above thesis, research-oriented interest
groups could perhaps take on the task of disproving Goedel's
incompleteness theorem [incomplete], and in doing so, put an end to
all bugs.
Acknowledgements
The authors wish to thank Bert Hubert, Peter van Dijk, and Saku Ytti
for pointing out the many errors Job introduced during the
preparation of this document.
Authors' Addresses
Job Snijders
Fastly
Amsterdam
Netherlands
Email: job@fastly.com
Chris Morrow
Google
Reston, Virginia
United States of America
Email: morrowc@ops-netman.net
Remco van Mook
Asteroid
Deventer
Netherlands
Email: remco@asteroidhq.com