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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 <tr class="field"><th class="field-name">Version:</th><td class="field-body">1.7</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-0058.txt?cvsroot=gentoo">2010/01/31 07:53:30</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">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 <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 </tr>
48 <tr class="field"><th class="field-name">Post-History:</th><td class="field-body">December 2009, January 2010</td>
49 </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="id2">Abstract</a></li>
57 <li><a class="reference internal" href="#motivation" id="id3">Motivation</a></li>
58 <li><a class="reference internal" href="#specification" id="id4">Specification</a><ul>
59 <li><a class="reference internal" href="#procedure-for-creating-the-metamanifest-file" id="id5">Procedure for creating the MetaManifest file:</a><ul>
60 <li><a class="reference internal" href="#summary" id="id6">Summary:</a></li>
61 <li><a class="reference internal" href="#process" id="id7">Process:</a></li>
62 <li><a class="reference internal" href="#notes" id="id8">Notes:</a></li>
63 </ul>
64 </li>
65 <li><a class="reference internal" href="#verification-of-one-or-more-items-from-the-metamanifest" id="id9">Verification of one or more items from the MetaManifest:</a></li>
66 <li><a class="reference internal" href="#procedure-for-verifying-an-item-in-the-metamanifest" id="id10">Procedure for verifying an item in the MetaManifest:</a><ul>
67 <li><a class="reference internal" href="#id1" id="id11">Notes:</a></li>
68 </ul>
69 </li>
70 </ul>
71 </li>
72 <li><a class="reference internal" href="#implementation-notes" id="id12">Implementation Notes</a><ul>
73 <li><a class="reference internal" href="#metamanifest-and-the-new-manifest2-filetypes" id="id13">MetaManifest and the new Manifest2 filetypes</a></li>
74 <li><a class="reference internal" href="#timestamps-additional-distribution-of-metamanifest" id="id14">Timestamps &amp; Additional distribution of MetaManifest</a></li>
75 <li><a class="reference internal" href="#metamanifest-size-considerations" id="id15">MetaManifest size considerations</a></li>
76 </ul>
77 </li>
78 <li><a class="reference internal" href="#backwards-compatibility" id="id16">Backwards Compatibility</a></li>
79 <li><a class="reference internal" href="#thanks" id="id17">Thanks</a></li>
80 <li><a class="reference internal" href="#references" id="id18">References</a></li>
81 <li><a class="reference internal" href="#copyright" id="id19">Copyright</a></li>
82 </ul>
83 </div>
84 <div class="section" id="abstract">
85 <h1><a class="toc-backref" href="#id2">Abstract</a></h1>
86 <p>MetaManifest provides a means of verifiable distribution from Gentoo
87 Infrastructure to a user system, while data is conveyed over completely
88 untrusted networks and system, by extending the Manifest2 specification,
89 and adding a top-level Manifest file, with support for other nested
90 Manifests.</p>
91 </div>
92 <div class="section" id="motivation">
93 <h1><a class="toc-backref" href="#id3">Motivation</a></h1>
94 <p>As part of a comprehensive security plan, we need a way to prove that
95 something originating from Gentoo as an organization (read Gentoo-owned
96 hardware, run by infrastructure), has not been tampered with. This
97 allows the usage of third-party rsync mirrors, without worrying that
98 they have modified something critical (e.g. eclasses, which are still
99 unsigned).</p>
100 <p>Securing the untrusted distribution is one of the easier tasks in the
101 security plan - in short, all that is required is having a hash of every
102 item in the tree, and signing that hash to prove it came from Gentoo.</p>
103 <p>Ironically we have a hashed and signed distribution (it's just not used
104 by most users, due to it's drawbacks): Our tree snapshot tarballs have
105 hashes and signatures.</p>
106 <p>So now we want to add the same verification to our material that is
107 distributed by rsync. We already provide hashes of subsets of the tree -
108 our Manifests protect individual packages. However metadata, eclasses
109 and profiles are not protected at this time. The directories of
110 packages and distfiles are NOT covered by this, as they are not
111 distributed by rsync.</p>
112 <p>This portion of the tree-signing work provides only the following
113 guarantee: A user can prove that the tree from the Gentoo infrastructure
114 has not been tampered with since leaving the Gentoo infrastructure.
115 No other guarantees, either implicit or explicit are made.</p>
116 <p>Additionally, distributing a set of the most recent MetaManifests from a
117 trusted source allows validation of trees that come from community
118 mirrors, and allows detection of all cases of malicious mirrors (either
119 by deliberate delay, replay [C08a, C08b] or alteration).</p>
120 </div>
121 <div class="section" id="specification">
122 <h1><a class="toc-backref" href="#id4">Specification</a></h1>
123 <p>For lack of a better name, the following solution should be known as the
124 MetaManifest. Those responsible for the name have already been sacked.</p>
125 <p>MetaManifest basically contains hashes of every file in the tree, either
126 directly or indirectly. The direct case applies to ANY file that does
127 not appear in an existing Manifest file (e.g. eclasses, Manifest files
128 themselves). The indirect case is covered by the CONTENTS of existing
129 Manifest files. If the Manifest itself is correct, we know that by
130 tracking the hash of the Manifest, we can be assured that the contents
131 are protected.</p>
132 <p>In the following, the MetaManifest file is a file named 'Manifest',
133 located at the root of a repository.</p>
134 <div class="section" id="procedure-for-creating-the-metamanifest-file">
135 <h2><a class="toc-backref" href="#id5">Procedure for creating the MetaManifest file:</a></h2>
136 <div class="section" id="summary">
137 <h3><a class="toc-backref" href="#id6">Summary:</a></h3>
138 <p>The objective of creating the MetaManifest file(s) is to ensure that
139 every single file in the tree occurs in at least one Manifest.</p>
140 </div>
141 <div class="section" id="process">
142 <h3><a class="toc-backref" href="#id7">Process:</a></h3>
143 <ol class="arabic simple">
144 <li>Start at the root of the Gentoo Portage tree (gentoo-x86, although
145 this procedure applies to overlays as well).</li>
146 <li>Initialize two unordered sets: COVERED, ALL.<ol class="arabic">
147 <li>'ALL' shall contain every file that exists in the present tree.</li>
148 <li>'COVERED' shall contain EVERY file that is mentioned in an existing
149 Manifest2. If a file is mentioned in a Manifest2, but does not
150 exist, it must still be included. No files should be excluded.</li>
151 </ol>
152 </li>
153 <li>Traverse the tree, depth-first.<ol class="arabic">
154 <li>At the top level only, ignore the following directories: distfiles,
155 packages, local.</li>
156 <li>If a directory contains a Manifest file, extract all relevant local
157 files from it (presently: AUX, MISC, EBUILD; but should follow the
158 evolution of Manifest2 entry types per [#GLEP60]), and place them
159 into the COVERED set.</li>
160 <li>Recursively add every file in the directory to the ALL set,
161 pursuant to the exclusion list as mentioned in [#GLEP60].</li>
162 </ol>
163 </li>
164 <li>Produce a new set, UNCOVERED, as the set-difference (ALL)-(COVERED).
165 This is every item that is not covered by another Manifest, or part
166 of an exclusion list.</li>
167 <li>If an existing MetaManifest file is present, remove it.</li>
168 <li>For each file in UNCOVERED, assign a Manifest2 type, produce the
169 hashes, and add with the filetype to the MetaManifest file.</li>
170 <li>For unique identification of the MetaManifest, a header line should
171 be included, using the exact contents of the metadata/timestamp.x
172 file, so that a MetaManifest may be tied back to a tree as
173 distributed by the rsync mirror system. The string of
174 'metadata/timestamp.x' should be included to identify this revision
175 of MetaManifest generation. e.g.:
176 &quot;Timestamp: metadata/timestamp.x: 1215722461 Thu Jul 10 20:41:01 2008 UTC&quot;
177 The package manager MUST not use the identifying string as a filename.</li>
178 <li>The MetaManifest must ultimately be GnuPG-signed.<ol class="arabic">
179 <li>For the initial implementation, the same key as used for snapshot
180 tarball signing is sufficient.</li>
181 <li>For the future, the key used for fully automated signing by infra
182 should not be on the same keyring as developer keys. See [#GLEPxx+3
183 for further notes].</li>
184 </ol>
185 </li>
186 </ol>
187 </div>
188 <div class="section" id="notes">
189 <h3><a class="toc-backref" href="#id8">Notes:</a></h3>
190 <p>The above does not conflict the proposal contained in GLEP33, which
191 restructure eclasses to include subdirectories and Manifest files, as
192 the Manifest rules above still provide indirect verification for all
193 files after the GLEP33 restructuring if it comes to pass.</p>
194 <p>Additional levels of Manifests are required, such as per-category, and
195 in the eclasses, profiles and metadata directories. This ensures that a
196 change to a singular file causes the smallest possible overall change in
197 the Manifests as propagated. Creation of the additional levels of
198 Manifests uses the same process as described above, simply starting at a
199 different root point.</p>
200 <p>MetaManifest generation will take place as part of the existing process
201 by infrastructure that takes the contents of CVS and prepares it for
202 distribution via rsync, which includes generating metadata. In-tree
203 Manifest files are not validated at this point, as they are assumed to
204 be correct.</p>
205 </div>
206 </div>
207 <div class="section" id="verification-of-one-or-more-items-from-the-metamanifest">
208 <h2><a class="toc-backref" href="#id9">Verification of one or more items from the MetaManifest:</a></h2>
209 <p>There are two times that this may happen: firstly, immediately after the
210 rsync has completed - this has the advantage that the kernel file cache
211 is hot, and checking the entire tree can be accomplished quickly.
212 Secondly, the MetaManifest should be checked during installation of a
213 package.</p>
214 </div>
215 <div class="section" id="procedure-for-verifying-an-item-in-the-metamanifest">
216 <h2><a class="toc-backref" href="#id10">Procedure for verifying an item in the MetaManifest:</a></h2>
217 <p>In the following, I've used term 'M2-verify' to note following the hash
218 verification procedures as defined by the Manifest2 format - which
219 compromise checking the file length, and that the hashes match. Which
220 filetypes may be ignored on missing is discussed in [#GLEP60].</p>
221 <ol class="arabic simple">
222 <li>Check the GnuPG signature on the MetaManifest against the keyring of
223 automated Gentoo keys. See [#GLEPxx+3] for full details regarding
224 verification of GnuPG signatures.
225 1. Abort if the signature check fails.</li>
226 <li>Check the Timestamp header. If it is significantly out of date
227 compared to the local clock or a trusted source, halt or require
228 manual intervention from the user.</li>
229 <li>For a verification of the tree following an rsync:<ol class="arabic">
230 <li>Build a set 'ALL' of every file covered by the rsync. (exclude
231 distfiles/, packages/, local/)</li>
232 <li>M2-verify every entry in the MetaManifest, descending into inferior
233 Manifests as needed. Place the relative path of every checked item
234 into a set 'COVERED'.</li>
235 <li>Construct the set 'UNCOVERED' by set-difference between the ALL and
236 COVERED sets.</li>
237 <li>For each file in the UNCOVERED set, assign a Manifest2 filetype.</li>
238 <li>If the filetype for any file in the UNCOVERED set requires a halt
239 on error, abort and display a suitable error.</li>
240 <li>Completed verification</li>
241 </ol>
242 </li>
243 <li>If checking at the installation of a package:<ol class="arabic">
244 <li>M2-verify the entry in MetaManifest for the Manifest</li>
245 <li>M2-verify all relevant metadata/ contents if metadata/ is being
246 used in any way (optionally done before dependency checking).</li>
247 <li>M2-verifying the contents of the Manifest.</li>
248 <li>Perform M2-verification of all eclasses and profiles used (both
249 directly and indirectly) by the ebuild.</li>
250 </ol>
251 </li>
252 </ol>
253 <div class="section" id="id1">
254 <h3><a class="toc-backref" href="#id11">Notes:</a></h3>
255 <ol class="arabic simple">
256 <li>For initial implementations, it is acceptable to check EVERY item in
257 the eclass and profiles directory, rather than tracking the exact
258 files used by every eclass (see note #2). Later implementations
259 should strive to only verify individual eclasses and profiles as
260 needed.</li>
261 <li>Tracking of exact files is of specific significance to the libtool
262 eclass, as it stores patches under eclass/ELT-patches, and as such
263 that would not be picked up by any tracing of the inherit function.
264 This may be alleviated by a later eclass and ebuild variable that
265 explicitly declares what files from the tree are used by a package.</li>
266 </ol>
267 </div>
268 </div>
269 </div>
270 <div class="section" id="implementation-notes">
271 <h1><a class="toc-backref" href="#id12">Implementation Notes</a></h1>
272 <p>For this portion of the tree-signing work, no actions are required of
273 the individual Gentoo developers. They will continue to develop and
274 commit as they do presently, and the MetaManifest is added by
275 Infrastructure during the tree generation process, and distributed to
276 users.</p>
277 <p>Any scripts generating Manifests and the MetaManifest may find it useful
278 to generate multiple levels of Manifests in parallel, and this is
279 explicitly permitted, provided that every file in the tree is covered by
280 at least one Manifest or the MetaManifest file. The uppermost
281 Manifest (MetaManifest) is the only item that does not occur in any
282 other Manifest file, but is instead GPG-signed to enable it's
283 validation.</p>
284 <div class="section" id="metamanifest-and-the-new-manifest2-filetypes">
285 <h2><a class="toc-backref" href="#id13">MetaManifest and the new Manifest2 filetypes</a></h2>
286 <p>While [#GLEP60] describes the addition of new filetypes, these are NOT
287 needed for implementation of the MetaManifest proposal. Without the new
288 filetypes, all entries in the MetaManifest would be of type 'MISC'.</p>
289 </div>
290 <div class="section" id="timestamps-additional-distribution-of-metamanifest">
291 <h2><a class="toc-backref" href="#id14">Timestamps &amp; Additional distribution of MetaManifest</a></h2>
292 <p>As discussed by [C08a,C08b], malicious third-party mirrors may use the
293 principles of exclusion and replay to deny an update to clients, while
294 at the same time recording the identity of clients to attack.</p>
295 <p>This should be guarded against by including a timestamp in the header of
296 the MetaManifest, as well as distributing the latest MetaManifests by a
297 trusted channel.</p>
298 <p>On all rsync mirrors directly maintained by the Gentoo infrastructure,
299 and not on community mirrors, there should be a new module
300 'gentoo-portage-metamanifests'. Within this module, all MetaManifests
301 for a recent time frame (e.g. one week) should be kept, named as
302 &quot;MetaManifest.$TS&quot;, where $TS is the timestamp from inside the file.
303 The most recent MetaManifest should always be symlinked as
304 MetaManifest.current. The possibility of serving the recent
305 MetaManifests via HTTPS should also be explored to mitigate
306 man-in-the-middle attacks.</p>
307 <p>The package manager should obtain MetaManifest.current and use it to
308 decide is the tree is too out of date per operation #2 of the
309 verification process. The decision about freshness should be a
310 user-configuration setting, with the ability to override.</p>
311 </div>
312 <div class="section" id="metamanifest-size-considerations">
313 <h2><a class="toc-backref" href="#id15">MetaManifest size considerations</a></h2>
314 <p>With only two levels of Manifests (per-package and top-level), every
315 rsync will cause a lot of traffic transferring the modified top-level
316 MetaManifest. To reduce this, first-level directory Manifests are
317 required. Alternatively, if the distribution method efficiently handles
318 small patch-like changes in an existing file, using an uncompressed
319 MetaManifest may be acceptable (this would primarily be distributed
320 version control systems). Other suggestions in reducing this traffic are
321 welcomed.</p>
322 </div>
323 </div>
324 <div class="section" id="backwards-compatibility">
325 <h1><a class="toc-backref" href="#id16">Backwards Compatibility</a></h1>
326 <ul class="simple">
327 <li>There are no backwards compatibility issues, as old versions of
328 Portage do not look for a Manifest file at the top level of the tree.</li>
329 <li>Manifest2-aware versions of Portage ignore all entries that they are
330 not certain how to handle. Enabling headers and PGP signing to be
331 conducted easily.</li>
332 </ul>
333 </div>
334 <div class="section" id="thanks">
335 <h1><a class="toc-backref" href="#id17">Thanks</a></h1>
336 <p>I'd like to thank the following people for input on this GLEP.</p>
337 <ul class="simple">
338 <li>Patrick Lauer (patrick): Prodding me to get all of the tree-signing
339 work finished, and helping to edit.</li>
340 <li>Ciaran McCreesh (ciaranm): Paludis Manifest2</li>
341 <li>Brian Harring (ferringb): pkgcore Manifest2</li>
342 <li>Marius Mauch (genone) &amp; Zac Medico (zmedico): Portage Manifest2</li>
343 <li>Ned Ludd (solar) - Security concept review</li>
344 </ul>
345 </div>
346 <div class="section" id="references">
347 <h1><a class="toc-backref" href="#id18">References</a></h1>
348 <dl class="docutils">
349 <dt>[C08a] Cappos, J et al. (2008). &quot;Package Management Security&quot;.</dt>
350 <dd>University of Arizona Technical Report TR08-02. Available online
351 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>
352 <dt>[C08b] Cappos, J et al. (2008). &quot;Attacks on Package Managers&quot;</dt>
353 <dd>Available online at:
354 <a class="reference external" href="http://www.cs.arizona.edu/people/justin/packagemanagersecurity/">http://www.cs.arizona.edu/people/justin/packagemanagersecurity/</a></dd>
355 </dl>
356 </div>
357 <div class="section" id="copyright">
358 <h1><a class="toc-backref" href="#id19">Copyright</a></h1>
359 <p>Copyright (c) 2006-2010 by Robin Hugh Johnson. This material may be
360 distributed only subject to the terms and conditions set forth in the
361 Open Publication License, v1.0.</p>
362 <p>vim: tw=72 ts=2 expandtab:</p>
363 </div>
364
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