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8 robbat2 1.1 <title>GLEP 58 -- Security of distribution of Gentoo software - Infrastructure to User distribution - MetaManifest</title>
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22     <table class="rfc2822 docutils field-list" frame="void" rules="none">
23     <col class="field-name" />
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25     <tbody valign="top">
26     <tr class="field"><th class="field-name">GLEP:</th><td class="field-body">58</td>
27     </tr>
28     <tr class="field"><th class="field-name">Title:</th><td class="field-body">Security of distribution of Gentoo software - Infrastructure to User distribution - MetaManifest</td>
29     </tr>
30 robbat2 1.3 <tr class="field"><th class="field-name">Version:</th><td class="field-body">1.6</td>
31 robbat2 1.1 </tr>
32 robbat2 1.3 <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-0058.txt?cvsroot=gentoo">2010/01/13 03:26:53</a></td>
33 robbat2 1.1 </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">Standards Track</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">Requires:</th><td class="field-body"><a class="reference external" href="http://www.gentoo.org/proj/en/glepglep-0044.html">44</a> <a class="reference external" href="http://www.gentoo.org/proj/en/glepglep-0060.html">60</a></td>
43     </tr>
44     <tr class="field"><th class="field-name">Created:</th><td class="field-body">October 2006</td>
45     </tr>
46 robbat2 1.2 <tr class="field"><th class="field-name">Updated:</th><td class="field-body">November 2007, June 2008, July 2008, October 2008, January 2010</td>
47 robbat2 1.1 </tr>
48 robbat2 1.3 <tr class="field"><th class="field-name">Post-History:</th><td class="field-body">December 2009</td>
49 robbat2 1.1 </tr>
50     </tbody>
51     </table>
52     <hr />
53     <div class="contents topic" id="contents">
54     <p class="topic-title first">Contents</p>
55     <ul class="simple">
56     <li><a class="reference internal" href="#abstract" id="id1">Abstract</a></li>
57     <li><a class="reference internal" href="#motivation" id="id2">Motivation</a></li>
58     <li><a class="reference internal" href="#specification" id="id3">Specification</a><ul>
59     <li><a class="reference internal" href="#procedure-for-creating-the-metamanifest-file" id="id4">Procedure for creating the MetaManifest file:</a></li>
60     <li><a class="reference internal" href="#verification-of-one-or-more-items-from-the-metamanifest" id="id5">Verification of one or more items from the MetaManifest:</a></li>
61     <li><a class="reference internal" href="#procedure-for-verifying-an-item-in-the-metamanifest" id="id6">Procedure for verifying an item in the MetaManifest:</a><ul>
62     <li><a class="reference internal" href="#notes" id="id7">Notes:</a></li>
63     </ul>
64     </li>
65     </ul>
66     </li>
67     <li><a class="reference internal" href="#implementation-notes" id="id8">Implementation Notes</a><ul>
68     <li><a class="reference internal" href="#metamanifest-and-the-new-manifest2-filetypes" id="id9">MetaManifest and the new Manifest2 filetypes</a></li>
69     <li><a class="reference internal" href="#timestamps-additional-distribution-of-metamanifest" id="id10">Timestamps &amp; Additional distribution of MetaManifest</a></li>
70     <li><a class="reference internal" href="#metamanifest-size-considerations" id="id11">MetaManifest size considerations</a></li>
71     </ul>
72     </li>
73     <li><a class="reference internal" href="#backwards-compatibility" id="id12">Backwards Compatibility</a></li>
74     <li><a class="reference internal" href="#thanks" id="id13">Thanks</a></li>
75     <li><a class="reference internal" href="#references" id="id14">References</a></li>
76     <li><a class="reference internal" href="#copyright" id="id15">Copyright</a></li>
77     </ul>
78     </div>
79     <div class="section" id="abstract">
80     <h1><a class="toc-backref" href="#id1">Abstract</a></h1>
81     <p>MetaManifest provides a means of verifiable distribution from Gentoo
82     Infrastructure to a user system, while data is conveyed over completely
83     untrusted networks and system, by extending the Manifest2 specification,
84     and adding a top-level Manifest file, with support for other nested
85     Manifests.</p>
86     </div>
87     <div class="section" id="motivation">
88     <h1><a class="toc-backref" href="#id2">Motivation</a></h1>
89     <p>As part of a comprehensive security plan, we need a way to prove that
90     something originating from Gentoo as an organization (read Gentoo-owned
91     hardware, run by infrastructure), has not been tampered with. This
92     allows the usage of third-party rsync mirrors, without worrying that
93     they have modified something critical (e.g. eclasses, which are still
94     unsigned).</p>
95     <p>Securing the untrusted distribution is one of the easier tasks in the
96     security plan - in short, all that is required is having a hash of every
97     item in the tree, and signing that hash to prove it came from Gentoo.</p>
98     <p>Ironically we have a hashed and signed distribution (it's just not used
99     by most users, due to it's drawbacks): Our tree snapshot tarballs have
100     hashes and signatures.</p>
101     <p>So now we want to add the same verification to our material that is
102     distributed by rsync. We already provide hashes of subsets of the tree -
103     our Manifests protect individual packages. However metadata, eclasses
104     and profiles are not protected at this time. The directories of
105     packages and distfiles are NOT covered by this, as they are not
106     distributed by rsync.</p>
107     <p>This portion of the tree-signing work provides only the following
108     guarantee: A user can prove that the tree from the Gentoo infrastructure
109     has not been tampered with since leaving the Gentoo infrastructure.
110     No other guarantees, either implicit or explicit are made.</p>
111     <p>Additionally, distributing a set of the most recent MetaManifests from a
112     trusted source allows validation of trees that come from community
113     mirrors, and allows detection of all cases of malicious mirrors (either
114     by deliberate delay, replay [C08a, C08b] or alteration).</p>
115     </div>
116     <div class="section" id="specification">
117     <h1><a class="toc-backref" href="#id3">Specification</a></h1>
118     <p>For lack of a better name, the following solution should be known as the
119     MetaManifest. Those responsible for the name have already been sacked.</p>
120     <p>MetaManifest basically contains hashes of every file in the tree, either
121     directly or indirectly. The direct case applies to ANY file that does
122     not appear in an existing Manifest file (e.g. eclasses, Manifest files
123     themselves). The indirect case is covered by the CONTENTS of existing
124     Manifest files. If the Manifest itself is correct, we know that by
125     tracking the hash of the Manifest, we can be assured that the contents
126     are protected.</p>
127     <p>In the following, the MetaManifest file is a file named 'Manifest',
128     located at the root of a repository.</p>
129     <div class="section" id="procedure-for-creating-the-metamanifest-file">
130     <h2><a class="toc-backref" href="#id4">Procedure for creating the MetaManifest file:</a></h2>
131     <ol class="arabic simple">
132     <li>Start at the root of the Gentoo Portage tree (gentoo-x86, although
133     this procedure applies to overlays as well).</li>
134     <li>Initialize two unordered sets: COVERED, ALL.<ol class="arabic">
135     <li>'ALL' will contain every file in the tree.</li>
136     <li>'COVERED' will contain every file that is mentioned in an existing
137     Manifest2.</li>
138     </ol>
139     </li>
140     <li>Traverse the tree, depth-first.<ol class="arabic">
141     <li>At the top level only, ignore the following directories: distfiles,
142     packages, local</li>
143     <li>If a directory contains a Manifest file, extract all relevant local
144     files from it (presently: AUX, MISC, EBUILD; but should follow the
145     evolution of Manifest2 entry types per [#GLEP60]), and place them
146     into the COVERED set.</li>
147     <li>Recursively add every file in the directory to the ALL set,
148 robbat2 1.3 pursuant to the exclusion list as mentioned in [#GLEP60].</li>
149 robbat2 1.1 </ol>
150     </li>
151     <li>Produce a new set, UNCOVERED, as the set-difference (ALL)-(COVERED).
152     This is every item that is not covered by another Manifest, or part
153     of an exclusion list.</li>
154     <li>If an existing MetaManifest file is present, remove it.</li>
155     <li>For each file in UNCOVERED, assign a Manifest2 type, produce the
156     hashes, and add with the filetype to the MetaManifest file.</li>
157     <li>For unique identification of the MetaManifest, a header line should
158     be included, using the exact contents of the metadata/timestamp.x
159     file, so that a MetaManifest may be tied back to a tree as
160     distributed by the rsync mirror system. The string of
161     'metadata/timestamp.x' should be included to identify this revision
162 robbat2 1.3 of MetaManifest generation. e.g.:
163 robbat2 1.1 &quot;Timestamp: metadata/timestamp.x: 1215722461 Thu Jul 10 20:41:01 2008 UTC&quot;
164     The package manager MUST not use the identifying string as a filename.</li>
165     <li>The MetaManifest must ultimately be GnuPG-signed.<ol class="arabic">
166     <li>For the initial implementation, the same key as used for snapshot
167     tarball signing is sufficient.</li>
168     <li>For the future, the key used for fully automated signing by infra
169     should not be on the same keyring as developer keys. See [#GLEPxx+3
170     for further notes].</li>
171     </ol>
172     </li>
173     </ol>
174     <p>The above does not conflict the proposal contained in GLEP33, which
175     restructure eclasses to include subdirectories and Manifest files, as
176     the Manifest rules above still provide indirect verification for all
177     files after the GLEP33 restructuring if it comes to pass.</p>
178 robbat2 1.2 <p>If other Manifests are added (such as per-category, per first-level
179 robbat2 1.3 directory, or protecting versioned eclasses), the size of the
180 robbat2 1.2 MetaManifest will be greatly reduced, and this specification was written
181     with such a possible future addition in mind.</p>
182 robbat2 1.1 <p>MetaManifest generation will take place as part of the existing process
183     by infrastructure that takes the contents of CVS and prepares it for
184     distribution via rsync, which includes generating metadata. In-tree
185     Manifest files are not checked at this point, as they are assumed to be
186     correct.</p>
187     </div>
188     <div class="section" id="verification-of-one-or-more-items-from-the-metamanifest">
189     <h2><a class="toc-backref" href="#id5">Verification of one or more items from the MetaManifest:</a></h2>
190     <p>There are two times that this may happen: firstly, immediately after the
191     rsync has completed - this has the advantage that the kernel file cache
192     is hot, and checking the entire tree can be accomplished quickly.
193     Secondly, the MetaManifest should be checked during installation of a
194     package.</p>
195     </div>
196     <div class="section" id="procedure-for-verifying-an-item-in-the-metamanifest">
197     <h2><a class="toc-backref" href="#id6">Procedure for verifying an item in the MetaManifest:</a></h2>
198     <p>In the following, I've used term 'M2-verify' to note following the hash
199     verification procedures as defined by the Manifest2 format - which
200     compromise checking the file length, and that the hashes match. Which
201     filetypes may be ignored on missing is discussed in [#GLEP60].</p>
202     <ol class="arabic simple">
203     <li>Check the GnuPG signature on the MetaManifest against the keyring of
204     automated Gentoo keys. See [#GLEPxx+3] for full details regarding
205     verification of GnuPG signatures.
206     1. Abort if the signature check fails.</li>
207 robbat2 1.3 <li>Check the Timestamp header. If it is significantly out of date
208 robbat2 1.1 compared to the local clock or a trusted source, halt or require
209     manual intervention from the user.</li>
210     <li>For a verification of the tree following an rsync:<ol class="arabic">
211     <li>Build a set 'ALL' of every file covered by the rsync. (exclude
212     distfiles/, packages/, local/)</li>
213     <li>M2-verify every entry in the MetaManifest, descending into inferior
214     Manifests as needed. Place the relative path of every checked item
215     into a set 'COVERED'.</li>
216     <li>Construct the set 'UNCOVERED' by set-difference between the ALL and
217     COVERED sets.</li>
218     <li>For each file in the UNCOVERED set, assign a Manifest2 filetype.</li>
219     <li>If the filetype for any file in the UNCOVERED set requires a halt
220     on error, abort and display a suitable error.</li>
221     <li>Completed verification</li>
222     </ol>
223     </li>
224     <li>If checking at the installation of a package:<ol class="arabic">
225     <li>M2-verify the entry in MetaManifest for the Manifest</li>
226     <li>M2-verify all relevant metadata/ contents if metadata/ is being
227 robbat2 1.3 used in any way (optionally done before dependency checking).</li>
228 robbat2 1.1 <li>M2-verifying the contents of the Manifest.</li>
229     <li>Perform M2-verification of all eclasses and profiles used (both
230     directly and indirectly) by the ebuild.</li>
231     </ol>
232     </li>
233     </ol>
234     <div class="section" id="notes">
235     <h3><a class="toc-backref" href="#id7">Notes:</a></h3>
236     <ol class="arabic simple">
237     <li>For initial implementations, it is acceptable to check EVERY item in
238     the eclass and profiles directory, rather than tracking the exact
239     files used by every eclass (see note #2). Later implementations
240     should strive to only verify individual eclasses and profiles as
241     needed.</li>
242     <li>Tracking of exact files is of specific significance to the libtool
243     eclass, as it stores patches under eclass/ELT-patches, and as such
244     that would not be picked up by any tracing of the inherit function.
245     This may be alleviated by a later eclass and ebuild variable that
246     explicitly declares what files from the tree are used by a package.</li>
247     </ol>
248     </div>
249     </div>
250     </div>
251     <div class="section" id="implementation-notes">
252     <h1><a class="toc-backref" href="#id8">Implementation Notes</a></h1>
253     <p>For this portion of the tree-signing work, no actions are required of
254     the individual Gentoo developers. They will continue to develop and
255     commit as they do presently, and the MetaManifest is added by
256     Infrastructure during the tree generation process, and distributed to
257     users.</p>
258     <div class="section" id="metamanifest-and-the-new-manifest2-filetypes">
259     <h2><a class="toc-backref" href="#id9">MetaManifest and the new Manifest2 filetypes</a></h2>
260     <p>While [#GLEP60] describes the addition of new filetypes, these are NOT
261     needed for implementation of the MetaManifest proposal. Without the new
262     filetypes, all entries in the MetaManifest would be of type 'MISC'.</p>
263     </div>
264     <div class="section" id="timestamps-additional-distribution-of-metamanifest">
265     <h2><a class="toc-backref" href="#id10">Timestamps &amp; Additional distribution of MetaManifest</a></h2>
266     <p>As discussed by [C08a,C08b], malicious third-party mirrors may use the
267     principles of exclusion and replay to deny an update to clients, while
268     at the same time recording the identity of clients to attack.</p>
269     <p>This should be guarded against by including a timestamp in the header of
270     the MetaManifest, as well as distributing the latest MetaManifests by a
271     trusted channel.</p>
272     <p>On all rsync mirrors directly maintained by the Gentoo infrastructure,
273     and not on community mirrors, there should be a new module
274     'gentoo-portage-metamanifests'. Within this module, all MetaManifests
275 robbat2 1.3 for a recent time frame (e.g. one week) should be kept, named as
276 robbat2 1.1 &quot;MetaManifest.$TS&quot;, where $TS is the timestamp from inside the file.
277     The most recent MetaManifest should always be symlinked as
278     MetaManifest.current. The possibility of serving the recent
279 robbat2 1.3 MetaManifests via HTTPS should also be explored to mitigate
280     man-in-the-middle attacks.</p>
281 robbat2 1.1 <p>The package manager should obtain MetaManifest.current and use it to
282     decide is the tree is too out of date per operation #2 of the
283     verification process. The decision about freshness should be a
284     user-configuration setting, with the ability to override.</p>
285     </div>
286     <div class="section" id="metamanifest-size-considerations">
287     <h2><a class="toc-backref" href="#id11">MetaManifest size considerations</a></h2>
288     <p>With only two levels of Manifests (per-package and top-level), every
289 robbat2 1.3 rsync will cause a lot of traffic transferring the modified top-level
290 robbat2 1.2 MetaManifest. To reduce this, first-level directory Manifests are
291     strongly recommended. Alternatively, if the distribution method
292 robbat2 1.3 efficiently handles small patch-like changes in an existing file,
293 robbat2 1.2 using an uncompressed MetaManifest may be acceptable (this would
294     primarily be distributed version control systems). Other suggestions
295     in reducing this traffic are welcomed.</p>
296 robbat2 1.1 </div>
297     </div>
298     <div class="section" id="backwards-compatibility">
299     <h1><a class="toc-backref" href="#id12">Backwards Compatibility</a></h1>
300     <ul class="simple">
301     <li>There are no backwards compatibility issues, as old versions of
302     Portage do not look for a Manifest file at the top level of the tree.</li>
303     <li>Manifest2-aware versions of Portage ignore all entries that they are
304     not certain how to handle. Enabling headers and PGP signing to be
305     conducted easily.</li>
306     </ul>
307     </div>
308     <div class="section" id="thanks">
309     <h1><a class="toc-backref" href="#id13">Thanks</a></h1>
310     <p>I'd like to thank the following people for input on this GLEP.</p>
311     <ul class="simple">
312     <li>Patrick Lauer (patrick): Prodding me to get all of the tree-signing
313     work finished, and helping to edit.</li>
314     <li>Ciaran McCreesh (ciaranm): Paludis Manifest2</li>
315     <li>Brian Harring (ferringb): pkgcore Manifest2</li>
316     <li>Marius Mauch (genone) &amp; Zac Medico (zmedico): Portage Manifest2</li>
317     <li>Ned Ludd (solar) - Security concept review</li>
318     </ul>
319     </div>
320     <div class="section" id="references">
321     <h1><a class="toc-backref" href="#id14">References</a></h1>
322     <dl class="docutils">
323     <dt>[C08a] Cappos, J et al. (2008). &quot;Package Management Security&quot;.</dt>
324     <dd>University of Arizona Technical Report TR08-02. Available online
325     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>
326     <dt>[C08b] Cappos, J et al. (2008). &quot;Attacks on Package Managers&quot;</dt>
327     <dd>Available online at:
328     <a class="reference external" href="http://www.cs.arizona.edu/people/justin/packagemanagersecurity/">http://www.cs.arizona.edu/people/justin/packagemanagersecurity/</a></dd>
329     </dl>
330     </div>
331     <div class="section" id="copyright">
332     <h1><a class="toc-backref" href="#id15">Copyright</a></h1>
333 robbat2 1.3 <p>Copyright (c) 2006-2010 by Robin Hugh Johnson. This material may be
334 robbat2 1.1 distributed only subject to the terms and conditions set forth in the
335     Open Publication License, v1.0.</p>
336     <p>vim: tw=72 ts=2 expandtab:</p>
337     </div>
338    
339     </div>
340     <div class="footer">
341     <hr class="footer" />
342     <a class="reference external" href="glep-0058.txt">View document source</a>.
343 robbat2 1.3 Generated on: 2010-01-13 03:27 UTC.
344 robbat2 1.1 Generated by <a class="reference external" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference external" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
345    
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347     </body>
348     </html>

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