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26 <tr class="field"><th class="field-name">GLEP:</th><td class="field-body">57</td>
27 </tr>
28 <tr class="field"><th class="field-name">Title:</th><td class="field-body">Security of distribution of Gentoo software - Overview</td>
29 </tr>
30 <tr class="field"><th class="field-name">Version:</th><td class="field-body">1.1</td>
31 </tr>
32 <tr class="field"><th class="field-name">Last-Modified:</th><td class="field-body"><a class="reference external" href="http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/proj/en/glep/glep-0057.txt?cvsroot=gentoo">2008/10/21 23:30:47</a></td>
33 </tr>
34 <tr class="field"><th class="field-name">Author:</th><td class="field-body">Robin Hugh Johnson &lt;robbat2&#32;&#97;t&#32;gentoo.org&gt;</td>
35 </tr>
36 <tr class="field"><th class="field-name">Status:</th><td class="field-body">Draft</td>
37 </tr>
38 <tr class="field"><th class="field-name">Type:</th><td class="field-body">Informational</td>
39 </tr>
40 <tr class="field"><th class="field-name">Content-Type:</th><td class="field-body"><a class="reference external" href="glep-0002.html">text/x-rst</a></td>
41 </tr>
42 <tr class="field"><th class="field-name">Created:</th><td class="field-body">November 2005</td>
43 </tr>
44 <tr class="field"><th class="field-name">Updated:</th><td class="field-body">May 2006, October 2006, Novemeber 2007, June 2008, July 2008, October 2008</td>
45 </tr>
46 </tbody>
47 </table>
48 <hr />
49 <div class="contents topic" id="contents">
50 <p class="topic-title first">Contents</p>
51 <ul class="simple">
52 <li><a class="reference internal" href="#abstract" id="id1">Abstract</a></li>
53 <li><a class="reference internal" href="#motivation" id="id2">Motivation</a></li>
54 <li><a class="reference internal" href="#specification" id="id3">Specification</a><ul>
55 <li><a class="reference internal" href="#system-elements" id="id4">System Elements</a></li>
56 <li><a class="reference internal" href="#processes" id="id5">Processes</a></li>
57 <li><a class="reference internal" href="#attacks-against-processes" id="id6">Attacks against Processes</a></li>
58 <li><a class="reference internal" href="#security-for-processes" id="id7">Security for Processes</a></li>
59 </ul>
60 </li>
61 <li><a class="reference internal" href="#backwards-compatibility" id="id8">Backwards Compatibility</a></li>
62 <li><a class="reference internal" href="#endnote-history-of-tree-signing-in-gentoo" id="id9">Endnote: History of tree-signing in Gentoo</a></li>
63 <li><a class="reference internal" href="#thanks" id="id10">Thanks</a></li>
64 <li><a class="reference internal" href="#references" id="id11">References</a></li>
65 <li><a class="reference internal" href="#copyright" id="id12">Copyright</a></li>
66 </ul>
67 </div>
68 <div class="section" id="abstract">
69 <h1><a class="toc-backref" href="#id1">Abstract</a></h1>
70 <p>This is the first in a series of 4 GLEPs. It aims to define the actors
71 and problems in the Gentoo software distribution process, with a strong
72 emphasis on security. The concepts thus developed, will then be used in
73 the following GLEPs to describe a comprehensive security solution for
74 this distribution process that prevents trivial attacks and increases
75 the difficulty on more complex attacks.</p>
76 </div>
77 <div class="section" id="motivation">
78 <h1><a class="toc-backref" href="#id2">Motivation</a></h1>
79 <p>Since at mid-2002 (see endnote: &quot;History of tree-signing in Gentoo&quot;),
80 many discussions have taken place on the gentoo-dev mailing list and in
81 many other places to design and implement a security strategy for the
82 distribution of files by the Gentoo project.</p>
83 <p>Usually the goal of such proposals was and is to be able to securely
84 identify the data provided by Gentoo and prevent third parties (like a
85 compromised mirror) from delivering harmful data (be it as modified
86 ebuilds, executable shell code or any other form) to the users of the
87 Gentoo MetaDistribution.</p>
88 <p>These strategies can neither prevent a malicious or compromised upstream
89 from injecting &quot;bad&quot; programs, nor can they stop a rogue developer from
90 committing malicious ebuilds. What they can do is to reduce the attack
91 vectors so that for example a compromised mirror will be detected and no
92 tainted data will be executed on user's systems.</p>
93 <p>Gentoo's software distribution system as it presently stands, contains a
94 number of security shortcomings. The last discussion on the gentoo-dev
95 mailing list [<a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/38363">http://thread.gmane.org/gmane.linux.gentoo.devel/38363</a>]
96 contains a good overview of most of the issues. Summarized here:</p>
97 <blockquote>
98 <ul class="simple">
99 <li>Unverifiable executable code distributed:
100 The most obvious instance are eclasses, but there are many other bits
101 of the tree that are not signed at all right now. Modifying that data
102 is trivial.</li>
103 <li>Shortcomings of existing Manifest verification
104 A lack and enforcement of policies, combined with suboptimal support
105 in portage, makes it trivial to modify or replace the existing
106 Manifests.</li>
107 <li>Vulnerability of existing infrastructure to attacks.
108 The previous two items make it possible for a skilled attacker to
109 design an attack and then execute it against specific portions of
110 existing infrastructure (eg: Compromise a country-local rsync mirror,
111 and totally replace a package and it's Manifest).</li>
112 </ul>
113 </blockquote>
114 </div>
115 <div class="section" id="specification">
116 <h1><a class="toc-backref" href="#id3">Specification</a></h1>
117 <p>Security is not something that can be considered in isolation. It is
118 both an ongoing holistic process and lessons learnt by examining
119 previous shortcomings.</p>
120 <div class="section" id="system-elements">
121 <h2><a class="toc-backref" href="#id4">System Elements</a></h2>
122 <dl class="docutils">
123 <dt>There are a few entities to be considered:</dt>
124 <dd><ul class="first last simple">
125 <li>Upstream. The people who provide the program(s) or data we wish to
126 distribute.</li>
127 <li>Gentoo Developers. The people that package and test the things
128 provided by Upstream.</li>
129 <li>Gentoo Infrastructure. The people and hardware that allow the revision
130 control of metadata and distribution of the data and metadata provided
131 by Developers and Upstream.</li>
132 <li>Gentoo Mirrors. Hardware provided by external contributors that is not
133 or only marginally controlled by Gentoo Infrastructure. Needed to
134 achieve the scalability and performance needed for the substantial
135 Gentoo user base.</li>
136 <li>Gentoo Users. The people that use the Gentoo MetaDistribution.</li>
137 </ul>
138 </dd>
139 </dl>
140 <p>The data described here is usually programs and data files provided by
141 upstream; as this is a rather large amount of data it is usually
142 distributed over http or ftp from Gentoo Mirrors. This data is usually
143 labeled as &quot;distfiles&quot;. Metadata is all information describing how to
144 manipulate that data - it is usually called &quot;The Tree&quot; or &quot;The Portage
145 Tree&quot;, consists of many ebuilds, eclasses and supporting files and is
146 usually distributed over rsync. The central rsync servers are controlled
147 by Gentoo Infrastructure, but many third-party rsync mirrors exist that
148 help to reduce the load on those central servers. These extra mirrors
149 are not maintained by Gentoo Infrastructure.</p>
150 <p>Attacks may be conducted against any of these entities. Obviously
151 direct attacks against Upstream and Users are outside of the scope of
152 this series of GLEPs as they are not in any way controlled or
153 controllable by Gentoo - however attacks using Gentoo as a conduit
154 (including malicous mirrors) must be considered.</p>
155 </div>
156 <div class="section" id="processes">
157 <h2><a class="toc-backref" href="#id5">Processes</a></h2>
158 <p>There are two major processes in the distribution of Gentoo, where
159 security needs to be implemented:</p>
160 <blockquote>
161 <ul class="simple">
162 <li>Developer commits to version control systems controlled by
163 Infrastructure.</li>
164 <li>Tree and distfile distribution from Infrastructure to Users, via the
165 mirrors (this includes both HTTP and rsync distribution).</li>
166 </ul>
167 </blockquote>
168 <p>Both processes need their security improved. In [GLEPxx+2] we will discuss
169 how to improve the security of the first process. The relatively
170 speaking simpler process of file distribution will be described in
171 [GLEPxx+1]. Since it can be implemented without having to change the
172 workflow and behaviour of developers we hope to get it done in a
173 reasonably short timeframe.</p>
174 </div>
175 <div class="section" id="attacks-against-processes">
176 <h2><a class="toc-backref" href="#id6">Attacks against Processes</a></h2>
177 <p>Attacks against the process #1 may be as complex as a malicious or
178 compromised developer (stolen SSH keys, rooted systems), or as simple as
179 a patch from a user that does a little more than it claims, and is not
180 adequately reviewed.</p>
181 <p>Attacks against the process #2 may be as simple as a single rooted
182 mirror, distributing a modified tree to the users of that mirror - or
183 some alteration of upstream sources. These attacks have a low cost and
184 are very hard to discover unless all distributed data is transparently
185 signed.</p>
186 <p>A simple example of such an attack and a partial solution for eclasses
187 is presented in [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/24677">http://thread.gmane.org/gmane.linux.gentoo.devel/24677</a>
188 ]. It shows quite well that any non-Gentoo controlled rsync mirror can
189 modify executable code; as much of this code is per default run as root
190 a malicious mirror could compromise hundreds of systems per day - if
191 cloaked well enough, such an attack could run for weeks before being
192 noticed. As there are no effective safeguards right now users are left
193 with the choice of either syncing from the sometimes slow or even
194 unresponsive Gentoo-controlled rsync mirrors or risk being compromised
195 by syncing from one of the community-provided mirrors. We will show that
196 protection against this class of attacks is very easy to implement with
197 little added cost.</p>
198 <p>At the level of mirrors, addition of malicious content is not the only
199 attack. As discussed by Cappos et al [C08a,C08b], an attacker may use
200 exclusion and replay attacks, possibly only on a specific subset of
201 user to extend the window of opportunity on another exploit.</p>
202 </div>
203 <div class="section" id="security-for-processes">
204 <h2><a class="toc-backref" href="#id7">Security for Processes</a></h2>
205 <p>Protection for process #1 can never be complete (without major
206 modifications to our development process), as a malicious developer is
207 fully authorized to provide materials for distribution. Partial
208 protection can be gained by Portage and Infrastructure changes, but the
209 real improvements needed are developer education and continued
210 vigilance. This is further discussed in [GLEPxx+2].</p>
211 <p>This security is still limited in scope - protection against compromised
212 developers is very expensive, and even complex systems like peer review
213 / multiple signatures can be broken by colluding developers. There are many
214 issues, be it social or technical, that increase the cost of such
215 measures a lot while only providing marginal security gains. Any
216 implementation proposal must be carefully analysed to find the best
217 security to developer hassle ratio.</p>
218 <p>Protection for process #2 is a different matter entirely. While it also
219 cannot be complete (as the User may be attacked directly), we can ensure
220 that Gentoo infrastructure and the mirrors are not a weak point. This
221 objective is actually much closer than it seems already - most of the
222 work has been completed for other things!. This is further discussed in
223 [GLEP58]. As this process has the most to gain in security, and the
224 most immediate impact, it should be implemented before or at the same
225 time as any changes to process #1. Security at this layer is already
226 available in the signed daily snapshots, but we can extend it to cover
227 the rsync mirrors as well.</p>
228 <p>Requirements pertaining to and management of keys (OpenPGP or otherwise)
229 is an issue that affects both processes, and is broken out into a
230 separate GLEP due to the technical complexity of the subject.
231 This deals with everything including: types of keys to use; usage
232 guidelines; procedures for managing signatures and trust for keys,
233 including cases of lost (destroyed) and stolen (or otherwise turned
234 malicious) keys.</p>
235 </div>
236 </div>
237 <div class="section" id="backwards-compatibility">
238 <h1><a class="toc-backref" href="#id8">Backwards Compatibility</a></h1>
239 <p>As an informational GLEP, this document has no direct impact on
240 backwards compatibility. However the related in-depth documents may
241 delve further into any issues of backwards compatibility.</p>
242 </div>
243 <div class="section" id="endnote-history-of-tree-signing-in-gentoo">
244 <h1><a class="toc-backref" href="#id9">Endnote: History of tree-signing in Gentoo</a></h1>
245 <p>This is a brief review of every previous tree-signing discussion, the
246 stuff before 2003-04-03 was very hard to come by, so I apologize if I've
247 missed a discussion (I would like to hear about it). I think there was
248 a very early private discussion with drobbins in 2001, as it's vaguely
249 referenced, but I can't find it anywhere.</p>
250 <p>2002-06-06, gentoo-dev mailing list, users first ask about signing of
251 ebuilds:
252 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/1950">http://thread.gmane.org/gmane.linux.gentoo.devel/1950</a> ]</p>
253 <p>2003-01-13, gentoo-dev mailing list, &quot;Re: Verifying portage is from
254 Gentoo&quot; - Paul de Vrieze (pauldv):
255 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/6619/focus=6619">http://thread.gmane.org/gmane.linux.gentoo.devel/6619/focus=6619</a> ]</p>
256 <p>2003-04, GWN articles announcing tree signing:
257 [ <a class="reference external" href="http://www.gentoo.org/news/en/gwn/20030407-newsletter.xml#doc_chap1_sect3">http://www.gentoo.org/news/en/gwn/20030407-newsletter.xml#doc_chap1_sect3</a> ]
258 [ <a class="reference external" href="http://www.gentoo.org/news/en/gwn/20030421-newsletter.xml#doc_chap1_sect2">http://www.gentoo.org/news/en/gwn/20030421-newsletter.xml#doc_chap1_sect2</a> ]</p>
259 <p>2003-04, gentoo-security mailing list, &quot;The state of ebuild signing
260 in portage&quot; - Joshua Brindle (method), the first suggestion of signed Manifests,
261 but also an unusual key-trust model:
262 [ <a class="reference external" href="http://marc.theaimsgroup.com/?l=gentoo-security&amp;m=105073449619892&amp;w=2">http://marc.theaimsgroup.com/?l=gentoo-security&amp;m=105073449619892&amp;w=2</a> ]</p>
263 <p>2003-04, gentoo-core mailing list, &quot;New Digests and Signing -- Attempted Explanation&quot;</p>
264 <p>2003-06, gentoo-core mailing list, &quot;A quick guide to GPG and key
265 signing.&quot; - This overview was one of the first to help developers see
266 how to use their devs, and was mainly intended for keysigning meetups.</p>
267 <p>2003-08-09, gentoo-core mailing list, &quot;Ebuild signing&quot; - status query,
268 with an not very positive response, delayed by Nick Jones (carpaski)
269 getting rooted and a safe cleanup taking a long time to affect.</p>
270 <p>2003-12-02, gentoo-core mailing list, &quot;Report: rsync1.it.gentoo.org compromised&quot;</p>
271 <p>2003-12-03, gentoo-core mailing list, &quot;Signing of ebuilds&quot;</p>
272 <p>2003-12-07, gentoo-core mailing list, &quot;gpg signing of Manifests&quot;, thread
273 includes the first GnuPG signing prototype code, by Robin H. Johnson
274 (robbat2). Andrew Cowie (rac) also produces a proof-of-concept around
275 this time.</p>
276 <p>2004-03-23, gentoo-dev mailing list, &quot;2004.1 will not include a secure
277 portage&quot; - Kurt Lieber (klieber). Signing is nowhere near ready for
278 2004.1 release, and it is realized that it there is insufficient traction
279 and the problem is very large. Many arguments about the checking and
280 verification side. First warning signs that MD5 might be broken in the
281 near future.
282 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/16876">http://thread.gmane.org/gmane.linux.gentoo.devel/16876</a> ]</p>
283 <p>2004-03-25, gentoo-dev mailing list, &quot;Redux: 2004.1 will not include a
284 secure portage&quot; - Robin H. Johnson (robbat2). Yet another proposal,
285 summarizing the points of the previous thread and this time trying to
286 track the various weaknesses.
287 <a class="reference external" href="http://marc.theaimsgroup.com/?l=gentoo-dev&amp;m=108017986400698&amp;w=2">http://marc.theaimsgroup.com/?l=gentoo-dev&amp;m=108017986400698&amp;w=2</a></p>
288 <p>2004-05-31, Gentoo managers meeting, portage team reports that
289 FEATURES=sign is now available, but large questions still exist over
290 verification policies and procedures, as well as handing of keys.
291 [ <a class="reference external" href="http://www.gentoo.org/proj/en/devrel/manager-meetings/logs/2004/20040531.txt">http://www.gentoo.org/proj/en/devrel/manager-meetings/logs/2004/20040531.txt</a> ]</p>
292 <p>2005-01-17, gentoo-core mailing list, &quot;Global objective for 2005 :
293 portage signing&quot;. Thierry Carrez (koon) suggests that more go into
294 tree-signing work. Problems at the time later in the thread show that
295 the upstream gpg-agent is not ready, amongst other minor implementation
296 issues.</p>
297 <p>2005-02-20, gentoo-dev mailing list, &quot;post-LWE 2005&quot; - Brian Harring
298 (ferringb). A discussion on the ongoing lack of signing, and that
299 eclasses and profiles need to be signed as well, but this seems to be
300 hanging on GLEP33 in the meantime.
301 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/25556/focus=25596">http://thread.gmane.org/gmane.linux.gentoo.devel/25556/focus=25596</a> ]</p>
302 <p>2005-03-08, gentoo-core mailing list, &quot;gpg manifest signing stats&quot;.
303 Informal statistics show that 26% of packages in the tree include a
304 signed Manifest. Questions are raised regarding key types, and key
305 policies.</p>
306 <p>2005-11-16, gentoo-core mailing list, &quot;Gentoo key signing practices and
307 official Gentoo keyring&quot;. A discussion of key handling and other
308 outstanding issues, also mentioning partial Manifests, as well as a
309 comparision between the signing procedures used in Slackware, Debian and
310 RPM-based distros.</p>
311 <p>2005-11-19, gentoo-portage-dev mailing list, &quot;Manifest signing&quot; - Robin
312 H. Johnson (robbat2) follows up the previous -core posting, discussion
313 implementation issues.
314 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.portage.devel/1401">http://thread.gmane.org/gmane.linux.gentoo.portage.devel/1401</a> ]</p>
315 <p>2006-05-18, gentoo-dev mailing list, &quot;Signing everything, for fun and for
316 profit&quot; - Patrick Lauer (bonsaikitten). Later brings up that Manifest2 is needed for
317 getting everything right.
318 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/38363">http://thread.gmane.org/gmane.linux.gentoo.devel/38363</a> ]</p>
319 <p>2006-05-19, gentoo-dev mailing list, &quot;Re: Signing everything, for fun and for
320 profit&quot; - Robin H. Johnson (robbat2). An introduction into some of the
321 OpenPGP standard, with a focus on how it affects file signing, key
322 signing, management of keys, and revocation.
323 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/38363/focus=38371">http://thread.gmane.org/gmane.linux.gentoo.devel/38363/focus=38371</a> ]</p>
324 <p>2007-04-11, gentoo-dev mailing list, &quot;Re: <em>DEVELOPMENT</em> mail list,
325 right?&quot; - Robin H. Johnson (robbat2). A progress report on these very
326 GLEPs.
327 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/47752/focus=47908">http://thread.gmane.org/gmane.linux.gentoo.devel/47752/focus=47908</a> ]</p>
328 <p>2007-07-02, gentoo-dev mailing list, &quot;Re: Re: Nominations open for the
329 Gentoo Council 2007/08&quot; - Robin H. Johnson (robbat2). Another progress
330 report.
331 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/50029/focus=50043">http://thread.gmane.org/gmane.linux.gentoo.devel/50029/focus=50043</a> ]</p>
332 <p>2007-11-30, portage-dev alias, &quot;Manifest2 and Tree-signing&quot; - Robin H.
333 Johnson (robbat2). First review thread for these GLEPs, many suggestions
334 from Marius Mauch (genone).</p>
335 <p>2008-04-03, gentoo-dev mailing list, &quot;Re: Monthly Gentoo Council
336 Reminder for April&quot; - Ciaran McCreesh (ciaranm). A thread in which
337 Ciaran reminds everybody that simply making all the developers sign the
338 tree is not sufficent to prevent all attacks.
339 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.devel/55508/focus=55542">http://thread.gmane.org/gmane.linux.gentoo.devel/55508/focus=55542</a> ]</p>
340 <p>2008-07-01, gentoo-portage-dev mailing list, &quot;proto-GLEPS for
341 Tree-signing&quot; - Robin H. Johnson (robbat2). Thread looking for review
342 input from Portage developers.
343 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.portage.devel/2686">http://thread.gmane.org/gmane.linux.gentoo.portage.devel/2686</a> ]</p>
344 <p>2008-07-12, gentoo-portage-dev mailing list, &quot;proto-GLEPS for
345 Tree-signing, take 2&quot; - Robin H. Johnson (robbat2). Integration of
346 changes from previous review, and a prototype for the signing code.
347 zmedico also posts a patch for a verification prototype.
348 [ <a class="reference external" href="http://thread.gmane.org/gmane.linux.gentoo.portage.devel/2709">http://thread.gmane.org/gmane.linux.gentoo.portage.devel/2709</a> ]</p>
349 </div>
350 <div class="section" id="thanks">
351 <h1><a class="toc-backref" href="#id10">Thanks</a></h1>
352 <p>I'd like to thank Patrick Lauer (bonsaikitten) for prodding me
353 to keep working on the tree-signing project, as well helping with
354 spelling, grammar, research (esp. tracking down every possible
355 vulnerability that has been mentioned in past discussions, and
356 integrating them in this overview).</p>
357 </div>
358 <div class="section" id="references">
359 <h1><a class="toc-backref" href="#id11">References</a></h1>
360 <dl class="docutils">
361 <dt>[C08a] Cappos, J et al. (2008). &quot;Package Management Security&quot;.</dt>
362 <dd>University of Arizona Technical Report TR08-02. Available online
363 from: <a class="reference external" href="ftp://ftp.cs.arizona.edu/reports/2008/TR08-02.pdf">ftp://ftp.cs.arizona.edu/reports/2008/TR08-02.pdf</a></dd>
364 <dt>[C08b] Cappos, J et al. (2008). &quot;Attacks on Package Managers&quot;</dt>
365 <dd>Available online at:
366 <a class="reference external" href="http://www.cs.arizona.edu/people/justin/packagemanagersecurity/">http://www.cs.arizona.edu/people/justin/packagemanagersecurity/</a></dd>
367 </dl>
368 </div>
369 <div class="section" id="copyright">
370 <h1><a class="toc-backref" href="#id12">Copyright</a></h1>
371 <p>Copyright (c) 2006 by Robin Hugh Johnson. This material may be
372 distributed only subject to the terms and conditions set forth in the
373 Open Publication License, v1.0.</p>
374 <p>vim: tw=72 ts=2 expandtab:</p>
375 </div>
377 </div>
378 <div class="footer">
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380 <a class="reference external" href="glep-0057.txt">View document source</a>.
381 Generated on: 2008-10-22 18:02 UTC.
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