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

Parent Directory Parent Directory | Revision Log Revision Log

Revision 1.1 - (hide annotations) (download)
Tue Oct 21 23:30:47 2008 UTC (9 years, 9 months ago) by cardoe
Branch: MAIN
File MIME type: text/plain
add Robin's tree signing gleps. They still need lots of editing love (some won't glep-ify) but at least they're here and have glep #s reserved

1 cardoe 1.1 GLEP: 58
2     Title: Security of distribution of Gentoo software - Infrastructure to User distribution - MetaManifest
3     Version: $Revision: 1.24 $
4     Last-Modified: $Date: 2008/10/09 23:23:12 $
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: ...
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.
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).
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.
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.
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.
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.
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).
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.
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.
72     In the following, the MetaManifest file is a file named 'Manifest',
73     located at the root of a repository.
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).
81     2. Initialize two unordered sets: COVERED, ALL.
82     2.1. 'ALL' will contain every file in the tree.
83     2.2. 'COVERED' will contain every file that is mentioned in an existing
84     Manifest2.
86     3. Traverse the tree, depth-first.
87     3.1. At the top level only, ignore the following directories: distfiles,
88     packages, local
89     3.2. If a directory contains a Manifest file, extract all relevant local
90     files from it (presently: AUX, MISC, EBUILD; but should follow the
91     evolution of Manifest2 entry types per [GLEPxx+5]), and place them
92     into the COVERED set.
93     3.3. Recursively add every file in the directory to the ALL set,
94     pursusant to the exclusion list as mentioned in [GLEPxx+5].
96     4. Produce a new set, UNCOVERED, as the set-difference (ALL)-(COVERED).
97     This is every item that is not covered by another Manifest, or part
98     of an exclusion list.
100     5. If an existing MetaManifest file is present, remove it.
102     6. For each file in UNCOVERED, assign a Manifest2 type, produce the
103     hashes, and add with the filetype to the MetaManifest file.
105     7. For unique identification of the MetaManifest, a header line should
106     be included, using the exact contents of the metadata/timestamp.x
107     file, so that a MetaManifest may be tied back to a tree as
108     distributed by the rsync mirror system. The string of
109     'metadata/timestamp.x' should be included to identify this revision
110     of MetaManifest generation. Eg:
111     "Timestamp: metadata/timestamp.x: 1215722461 Thu Jul 10 20:41:01 2008 UTC"
112     The package manager MUST not use the identifying string as a filename.
114     8. The MetaManifest must ultimately be GnuPG-signed.
115     8.1. For the initial implementation, the same key as used for snapshot
116     tarball signing is sufficient.
117     8.2. For the future, the key used for fully automated signing by infra
118     should not be on the same keyring as developer keys. See [GLEPxx+3
119     for further notes].
121     The above does not conflict the proposal contained in GLEP33, which
122     restructure eclasses to include subdirectories and Manifest files, as
123     the Manifest rules above still provide indirect verification for all
124     files after the GLEP33 restructuring if it comes to pass.
126     If other Manifests are added (such as per-category, or protecting
127     versioned eclases), the size of the MetaManifest will be greatly
128     reduced, and this specification was written with such a possible future
129     addition in mind.
131     MetaManifest generation will take place as part of the existing process
132     by infrastructure that takes the contents of CVS and prepares it for
133     distribution via rsync, which includes generating metadata. In-tree
134     Manifest files are not checked at this point, as they are assumed to be
135     correct.
137     --------------------------------------------------------
138     Verification of one or more items from the MetaManifest:
139     --------------------------------------------------------
140     There are two times that this may happen: firstly, immediately after the
141     rsync has completed - this has the advantage that the kernel file cache
142     is hot, and checking the entire tree can be accomplished quickly.
143     Secondly, the MetaManifest should be checked during installation of a
144     package.
146     ----------------------------------------------------
147     Procedure for verifying an item in the MetaManifest:
148     ----------------------------------------------------
149     In the following, I've used term 'M2-verify' to note following the hash
150     verification procedures as defined by the Manifest2 format - which
151     compromise checking the file length, and that the hashes match. Which
152     filetypes may be ignored on missing is discussed in [GLEPxx+5].
154     1. Check the GnuPG signature on the MetaManifest against the keyring of
155     automated Gentoo keys. See [GLEPxx+3] for full details regarding
156     verification of GnuPG signatures.
157     1.1. Abort if the signature check fails.
159     2. Check the Timestamp header. If it is significently out of date
160     compared to the local clock or a trusted source, halt or require
161     manual intervention from the user.
163     3. For a verification of the tree following an rsync:
164     3.1. Build a set 'ALL' of every file covered by the rsync. (exclude
165     distfiles/, packages/, local/)
166     3.2. M2-verify every entry in the MetaManifest, descending into inferior
167     Manifests as needed. Place the relative path of every checked item
168     into a set 'COVERED'.
169     3.3. Construct the set 'UNCOVERED' by set-difference between the ALL and
170     COVERED sets.
171     3.4. For each file in the UNCOVERED set, assign a Manifest2 filetype.
172     3.5. If the filetype for any file in the UNCOVERED set requires a halt
173     on error, abort and display a suitable error.
174     3.6. Completed verification
176     4. If checking at the installation of a package:
177     4.1. M2-verify the entry in MetaManifest for the Manifest
178     4.2. M2-verify all relevant metadata/ contents if metadata/ is being
179     used in any way (optionally done before dependancy checking).
180     4.3. M2-verifying the contents of the Manifest.
181     4.4. Perform M2-verification of all eclasses and profiles used (both
182     directly and indirectly) by the ebuild.
184     Notes:
185     ======
186     1. For initial implementations, it is acceptable to check EVERY item in
187     the eclass and profiles directory, rather than tracking the exact
188     files used by every eclass (see note #2). Later implementations
189     should strive to only verify individual eclasses and profiles as
190     needed.
191     2. Tracking of exact files is of specific significance to the libtool
192     eclass, as it stores patches under eclass/ELT-patches, and as such
193     that would not be picked up by any tracing of the inherit function.
194     This may be alleviated by a later eclass and ebuild variable that
195     explicitly declares what files from the tree are used by a package.
197     ====================
198     Implementation Notes
199     ====================
200     For this portion of the tree-signing work, no actions are required of
201     the individual Gentoo developers. They will continue to develop and
202     commit as they do presently, and the MetaManifest is added by
203     Infrastructure during the tree generation process, and distributed to
204     users.
206     --------------------------------------------
207     MetaManifest and the new Manifest2 filetypes
208     --------------------------------------------
209     While [GLEPxx+5] describes the addition of new filetypes, these are NOT
210     needed for implementation of the MetaManifest proposal. Without the new
211     filetypes, all entries in the MetaManifest would be of type 'MISC'.
213     ----------------------------------------------------
214     Timestamps & Additional distribution of MetaManifest
215     ----------------------------------------------------
216     As discussed by [C08a,C08b], malicious third-party mirrors may use the
217     principles of exclusion and replay to deny an update to clients, while
218     at the same time recording the identity of clients to attack.
220     This should be guarded against by including a timestamp in the header of
221     the MetaManifest, as well as distributing the latest MetaManifests by a
222     trusted channel.
224     On all rsync mirrors directly maintained by the Gentoo infrastructure,
225     and not on community mirrors, there should be a new module
226     'gentoo-portage-metamanifests'. Within this module, all MetaManifests
227     for a recent time frame (eg one week) should be kept, named as
228     "MetaManifest.$TS", where $TS is the timestamp from inside the file.
229     The most recent MetaManifest should always be symlinked as
230     MetaManifest.current. The possibility of serving the recent
231     MetaManifests via HTTPS should also be explored to mitigate MitM
232     attacks.
234     The package manager should obtain MetaManifest.current and use it to
235     decide is the tree is too out of date per operation #2 of the
236     verification process. The decision about freshness should be a
237     user-configuration setting, with the ability to override.
239     --------------------------------
240     MetaManifest size considerations
241     --------------------------------
242     With only two levels of Manifests (per-package and top-level), every
243     rsync will cause a lot of traffic transfering the modified top-level
244     MetaManifest. To reduce this, per-category Manifests are strongly
245     recommended. Alternatively, if the distribution method efficently
246     handles small patch-like changes in an existing file, using an
247     uncompressed MetaManifest may be acceptable (this would primarily be
248     distributed version control systems). Other suggestions in reducing this
249     traffic are welcomed.
251     =======================
252     Backwards Compatibility
253     =======================
254     - There are no backwards compatibility issues, as old versions of
255     Portage do not look for a Manifest file at the top level of the tree.
256     - Manifest2-aware versions of Portage ignore all entries that they are
257     not certain how to handle. Enabling headers and PGP signing to be
258     conducted easily.
260     ======
261     Thanks
262     ======
263     I'd like to thank the following people for input on this GLEP.
264     - Patrick Lauer (patrick): Prodding me to get all of the tree-signing
265     work finished, and helping to edit.
266     - Ciaran McCreesh (ciaranm): Paludis Manifest2
267     - Brian Harring (ferringb): pkgcore Manifest2
268     - Marius Mauch (genone) & Zac Medico (zmedico): Portage Manifest2
269     - Ned Ludd (solar) - Security concept review
271     ==========
272     References
273     ==========
275     [C08a] Cappos, J et al. (2008). "Package Management Security".
276     University of Arizona Technical Report TR08-02. Available online
277     from: ftp://ftp.cs.arizona.edu/reports/2008/TR08-02.pdf
278     [C08b] Cappos, J et al. (2008). "Attacks on Package Managers"
279     Available online at:
280     http://www.cs.arizona.edu/people/justin/packagemanagersecurity/
282     =========
283     Copyright
284     =========
285     Copyright (c) 2006 by Robin Hugh Johnson. This material may be
286     distributed only subject to the terms and conditions set forth in the
287     Open Publication License, v1.0.
289     vim: tw=72 ts=2 expandtab:

  ViewVC Help
Powered by ViewVC 1.1.20