/[gentoo]/xml/htdocs/proj/en/glep/glep-0058.txt
Gentoo

Contents of /xml/htdocs/proj/en/glep/glep-0058.txt

Parent Directory Parent Directory | Revision Log Revision Log


Revision 1.3 - (show annotations) (download)
Wed Oct 22 18:01:42 2008 UTC (6 years, 1 month ago) by robbat2
Branch: MAIN
Changes since 1.2: +19 -18 lines
File MIME type: text/plain
More RST validation fixes on tree-signing gleps.

1 GLEP: 58
2 Title: Security of distribution of Gentoo software - Infrastructure to User distribution - MetaManifest
3 Version: $Revision: 1.2 $
4 Last-Modified: $Date: 2008/10/22 17:59:43 $
5 Author: Robin Hugh Johnson <robbat2@gentoo.org>,
6 Status: Draft
7 Type: Standards Track
8 Content-Type: text/x-rst
9 Requires: GLEP44, GLEP60
10 Created: October 2006
11 Updated: November 2007, June 2008, July 2008, October 2008
12 Post-History: ...
13
14 ========
15 Abstract
16 ========
17 MetaManifest provides a means of verifiable distribution from Gentoo
18 Infrastructure to a user system, while data is conveyed over completely
19 untrusted networks and system, by extending the Manifest2 specification,
20 and adding a top-level Manifest file, with support for other nested
21 Manifests.
22
23 ==========
24 Motivation
25 ==========
26 As part of a comprehensive security plan, we need a way to prove that
27 something originating from Gentoo as an organization (read Gentoo-owned
28 hardware, run by infrastructure), has not been tampered with. This
29 allows the usage of third-party rsync mirrors, without worrying that
30 they have modified something critical (e.g. eclasses, which are still
31 unsigned).
32
33 Securing the untrusted distribution is one of the easier tasks in the
34 security plan - in short, all that is required is having a hash of every
35 item in the tree, and signing that hash to prove it came from Gentoo.
36
37 Ironically we have a hashed and signed distribution (it's just not used
38 by most users, due to it's drawbacks): Our tree snapshot tarballs have
39 hashes and signatures.
40
41 So now we want to add the same verification to our material that is
42 distributed by rsync. We already provide hashes of subsets of the tree -
43 our Manifests protect individual packages. However metadata, eclasses
44 and profiles are not protected at this time. The directories of
45 packages and distfiles are NOT covered by this, as they are not
46 distributed by rsync.
47
48 This portion of the tree-signing work provides only the following
49 guarantee: A user can prove that the tree from the Gentoo infrastructure
50 has not been tampered with since leaving the Gentoo infrastructure.
51 No other guarantees, either implicit or explicit are made.
52
53 Additionally, distributing a set of the most recent MetaManifests from a
54 trusted source allows validation of trees that come from community
55 mirrors, and allows detection of all cases of malicious mirrors (either
56 by deliberate delay, replay [C08a, C08b] or alteration).
57
58 =============
59 Specification
60 =============
61 For lack of a better name, the following solution should be known as the
62 MetaManifest. Those responsible for the name have already been sacked.
63
64 MetaManifest basically contains hashes of every file in the tree, either
65 directly or indirectly. The direct case applies to ANY file that does
66 not appear in an existing Manifest file (e.g. eclasses, Manifest files
67 themselves). The indirect case is covered by the CONTENTS of existing
68 Manifest files. If the Manifest itself is correct, we know that by
69 tracking the hash of the Manifest, we can be assured that the contents
70 are protected.
71
72 In the following, the MetaManifest file is a file named 'Manifest',
73 located at the root of a repository.
74
75 ---------------------------------------------
76 Procedure for creating the MetaManifest file:
77 ---------------------------------------------
78 1. Start at the root of the Gentoo Portage tree (gentoo-x86, although
79 this procedure applies to overlays as well).
80
81 2. Initialize two unordered sets: COVERED, ALL.
82
83 1. 'ALL' will contain every file in the tree.
84 2. 'COVERED' will contain every file that is mentioned in an existing
85 Manifest2.
86
87 3. Traverse the tree, depth-first.
88
89 1. At the top level only, ignore the following directories: distfiles,
90 packages, local
91 2. If a directory contains a Manifest file, extract all relevant local
92 files from it (presently: AUX, MISC, EBUILD; but should follow the
93 evolution of Manifest2 entry types per [GLEPxx+5]), and place them
94 into the COVERED set.
95 3. Recursively add every file in the directory to the ALL set,
96 pursusant to the exclusion list as mentioned in [GLEPxx+5].
97
98 4. Produce a new set, UNCOVERED, as the set-difference (ALL)-(COVERED).
99 This is every item that is not covered by another Manifest, or part
100 of an exclusion list.
101
102 5. If an existing MetaManifest file is present, remove it.
103
104 6. For each file in UNCOVERED, assign a Manifest2 type, produce the
105 hashes, and add with the filetype to the MetaManifest file.
106
107 7. For unique identification of the MetaManifest, a header line should
108 be included, using the exact contents of the metadata/timestamp.x
109 file, so that a MetaManifest may be tied back to a tree as
110 distributed by the rsync mirror system. The string of
111 'metadata/timestamp.x' should be included to identify this revision
112 of MetaManifest generation. Eg:
113 "Timestamp: metadata/timestamp.x: 1215722461 Thu Jul 10 20:41:01 2008 UTC"
114 The package manager MUST not use the identifying string as a filename.
115
116 8. The MetaManifest must ultimately be GnuPG-signed.
117
118 1. For the initial implementation, the same key as used for snapshot
119 tarball signing is sufficient.
120 2. For the future, the key used for fully automated signing by infra
121 should not be on the same keyring as developer keys. See [GLEPxx+3
122 for further notes].
123
124 The above does not conflict the proposal contained in GLEP33, which
125 restructure eclasses to include subdirectories and Manifest files, as
126 the Manifest rules above still provide indirect verification for all
127 files after the GLEP33 restructuring if it comes to pass.
128
129 If other Manifests are added (such as per-category, or protecting
130 versioned eclases), the size of the MetaManifest will be greatly
131 reduced, and this specification was written with such a possible future
132 addition in mind.
133
134 MetaManifest generation will take place as part of the existing process
135 by infrastructure that takes the contents of CVS and prepares it for
136 distribution via rsync, which includes generating metadata. In-tree
137 Manifest files are not checked at this point, as they are assumed to be
138 correct.
139
140 --------------------------------------------------------
141 Verification of one or more items from the MetaManifest:
142 --------------------------------------------------------
143 There are two times that this may happen: firstly, immediately after the
144 rsync has completed - this has the advantage that the kernel file cache
145 is hot, and checking the entire tree can be accomplished quickly.
146 Secondly, the MetaManifest should be checked during installation of a
147 package.
148
149 ----------------------------------------------------
150 Procedure for verifying an item in the MetaManifest:
151 ----------------------------------------------------
152 In the following, I've used term 'M2-verify' to note following the hash
153 verification procedures as defined by the Manifest2 format - which
154 compromise checking the file length, and that the hashes match. Which
155 filetypes may be ignored on missing is discussed in [GLEPxx+5].
156
157 1. Check the GnuPG signature on the MetaManifest against the keyring of
158 automated Gentoo keys. See [GLEPxx+3] for full details regarding
159 verification of GnuPG signatures.
160 1. Abort if the signature check fails.
161
162 2. Check the Timestamp header. If it is significently out of date
163 compared to the local clock or a trusted source, halt or require
164 manual intervention from the user.
165
166 3. For a verification of the tree following an rsync:
167
168 1. Build a set 'ALL' of every file covered by the rsync. (exclude
169 distfiles/, packages/, local/)
170 2. M2-verify every entry in the MetaManifest, descending into inferior
171 Manifests as needed. Place the relative path of every checked item
172 into a set 'COVERED'.
173 3. Construct the set 'UNCOVERED' by set-difference between the ALL and
174 COVERED sets.
175 4. For each file in the UNCOVERED set, assign a Manifest2 filetype.
176 5. If the filetype for any file in the UNCOVERED set requires a halt
177 on error, abort and display a suitable error.
178 6. Completed verification
179
180 4. If checking at the installation of a package:
181
182 1. M2-verify the entry in MetaManifest for the Manifest
183 2. M2-verify all relevant metadata/ contents if metadata/ is being
184 used in any way (optionally done before dependancy checking).
185 3. M2-verifying the contents of the Manifest.
186 4. Perform M2-verification of all eclasses and profiles used (both
187 directly and indirectly) by the ebuild.
188
189 Notes:
190 ======
191 1. For initial implementations, it is acceptable to check EVERY item in
192 the eclass and profiles directory, rather than tracking the exact
193 files used by every eclass (see note #2). Later implementations
194 should strive to only verify individual eclasses and profiles as
195 needed.
196 2. Tracking of exact files is of specific significance to the libtool
197 eclass, as it stores patches under eclass/ELT-patches, and as such
198 that would not be picked up by any tracing of the inherit function.
199 This may be alleviated by a later eclass and ebuild variable that
200 explicitly declares what files from the tree are used by a package.
201
202 ====================
203 Implementation Notes
204 ====================
205 For this portion of the tree-signing work, no actions are required of
206 the individual Gentoo developers. They will continue to develop and
207 commit as they do presently, and the MetaManifest is added by
208 Infrastructure during the tree generation process, and distributed to
209 users.
210
211 --------------------------------------------
212 MetaManifest and the new Manifest2 filetypes
213 --------------------------------------------
214 While [GLEPxx+5] describes the addition of new filetypes, these are NOT
215 needed for implementation of the MetaManifest proposal. Without the new
216 filetypes, all entries in the MetaManifest would be of type 'MISC'.
217
218 ----------------------------------------------------
219 Timestamps & Additional distribution of MetaManifest
220 ----------------------------------------------------
221 As discussed by [C08a,C08b], malicious third-party mirrors may use the
222 principles of exclusion and replay to deny an update to clients, while
223 at the same time recording the identity of clients to attack.
224
225 This should be guarded against by including a timestamp in the header of
226 the MetaManifest, as well as distributing the latest MetaManifests by a
227 trusted channel.
228
229 On all rsync mirrors directly maintained by the Gentoo infrastructure,
230 and not on community mirrors, there should be a new module
231 'gentoo-portage-metamanifests'. Within this module, all MetaManifests
232 for a recent time frame (eg one week) should be kept, named as
233 "MetaManifest.$TS", where $TS is the timestamp from inside the file.
234 The most recent MetaManifest should always be symlinked as
235 MetaManifest.current. The possibility of serving the recent
236 MetaManifests via HTTPS should also be explored to mitigate MitM
237 attacks.
238
239 The package manager should obtain MetaManifest.current and use it to
240 decide is the tree is too out of date per operation #2 of the
241 verification process. The decision about freshness should be a
242 user-configuration setting, with the ability to override.
243
244 --------------------------------
245 MetaManifest size considerations
246 --------------------------------
247 With only two levels of Manifests (per-package and top-level), every
248 rsync will cause a lot of traffic transfering the modified top-level
249 MetaManifest. To reduce this, per-category Manifests are strongly
250 recommended. Alternatively, if the distribution method efficently
251 handles small patch-like changes in an existing file, using an
252 uncompressed MetaManifest may be acceptable (this would primarily be
253 distributed version control systems). Other suggestions in reducing this
254 traffic are welcomed.
255
256 =======================
257 Backwards Compatibility
258 =======================
259 - There are no backwards compatibility issues, as old versions of
260 Portage do not look for a Manifest file at the top level of the tree.
261 - Manifest2-aware versions of Portage ignore all entries that they are
262 not certain how to handle. Enabling headers and PGP signing to be
263 conducted easily.
264
265 ======
266 Thanks
267 ======
268 I'd like to thank the following people for input on this GLEP.
269
270 - Patrick Lauer (patrick): Prodding me to get all of the tree-signing
271 work finished, and helping to edit.
272 - Ciaran McCreesh (ciaranm): Paludis Manifest2
273 - Brian Harring (ferringb): pkgcore Manifest2
274 - Marius Mauch (genone) & Zac Medico (zmedico): Portage Manifest2
275 - Ned Ludd (solar) - Security concept review
276
277 ==========
278 References
279 ==========
280
281 [C08a] Cappos, J et al. (2008). "Package Management Security".
282 University of Arizona Technical Report TR08-02. Available online
283 from: ftp://ftp.cs.arizona.edu/reports/2008/TR08-02.pdf
284 [C08b] Cappos, J et al. (2008). "Attacks on Package Managers"
285 Available online at:
286 http://www.cs.arizona.edu/people/justin/packagemanagersecurity/
287
288 =========
289 Copyright
290 =========
291 Copyright (c) 2006 by Robin Hugh Johnson. This material may be
292 distributed only subject to the terms and conditions set forth in the
293 Open Publication License, v1.0.
294
295 vim: tw=72 ts=2 expandtab:

  ViewVC Help
Powered by ViewVC 1.1.20