[jackhill/guix/guix.git] / guix / git-authenticate.scm

;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2019, 2020 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

(define-module (guix git-authenticate)
  #:use-module (git)
  #:autoload   (gcrypt hash) (sha256)
  #:use-module (guix base16)
  #:autoload   (guix base64) (base64-encode)
  #:use-module ((guix git)
                #:select (commit-difference false-if-git-not-found))
  #:use-module (guix i18n)
  #:use-module (guix openpgp)
  #:use-module ((guix utils)
                #:select (cache-directory with-atomic-file-output))
  #:use-module ((guix build utils)
                #:select (mkdir-p))
  #:use-module (guix progress)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-11)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-34)
  #:use-module (srfi srfi-35)
  #:use-module (rnrs bytevectors)
  #:use-module (rnrs io ports)
  #:use-module (ice-9 match)
  #:autoload   (ice-9 pretty-print) (pretty-print)
  #:export (read-authorizations
            commit-signing-key
            commit-authorized-keys
            authenticate-commit
            authenticate-commits
            load-keyring-from-reference
            previously-authenticated-commits
            cache-authenticated-commit

            repository-cache-key
            authenticate-repository

            git-authentication-error?
            git-authentication-error-commit
            unsigned-commit-error?
            unauthorized-commit-error?
            unauthorized-commit-error-signing-key
            signature-verification-error?
            signature-verification-error-keyring
            signature-verification-error-signature
            missing-key-error?
            missing-key-error-signature))

;;; Commentary:
;;;
;;; This module provides tools to authenticate a range of Git commits.  A
;;; commit is considered "authentic" if and only if it is signed by an
;;; authorized party.  Parties authorized to sign a commit are listed in the
;;; '.guix-authorizations' file of the parent commit.
;;;
;;; Code:

(define-condition-type &git-authentication-error &error
  git-authentication-error?
  (commit  git-authentication-error-commit))

(define-condition-type &unsigned-commit-error &git-authentication-error
  unsigned-commit-error?)

(define-condition-type &unauthorized-commit-error &git-authentication-error
  unauthorized-commit-error?
  (signing-key unauthorized-commit-error-signing-key))

(define-condition-type &signature-verification-error &git-authentication-error
  signature-verification-error?
  (signature signature-verification-error-signature)
  (keyring   signature-verification-error-keyring))

(define-condition-type &missing-key-error &git-authentication-error
  missing-key-error?
  (signature missing-key-error-signature))


(define* (commit-signing-key repo commit-id keyring
                             #:key (disallowed-hash-algorithms '(sha1)))
  "Return the OpenPGP key that signed COMMIT-ID (an OID).  Raise an exception
if the commit is unsigned, has an invalid signature, has a signature using one
of the hash algorithms in DISALLOWED-HASH-ALGORITHMS, or if its signing key is
not in KEYRING."
  (let-values (((signature signed-data)
                (catch 'git-error
                  (lambda ()
                    (commit-extract-signature repo commit-id))
                  (lambda _
                    (values #f #f)))))
    (unless signature
      (raise (condition
              (&unsigned-commit-error (commit commit-id))
              (&message
               (message (format #f (G_ "commit ~a lacks a signature")
                                (oid->string commit-id)))))))

    (let ((signature (string->openpgp-packet signature)))
      (when (memq (openpgp-signature-hash-algorithm signature)
                  `(,@disallowed-hash-algorithms md5))
        (raise (condition
                (&unsigned-commit-error (commit commit-id))
                (&message
                 (message (format #f (G_ "commit ~a has a ~a signature, \
which is not permitted")
                                  (oid->string commit-id)
                                  (openpgp-signature-hash-algorithm
                                   signature)))))))

      (with-fluids ((%default-port-encoding "UTF-8"))
        (let-values (((status data)
                      (verify-openpgp-signature signature keyring
                                                (open-input-string signed-data))))
          (match status
            ('bad-signature
             ;; There's a signature but it's invalid.
             (raise (condition
                     (&signature-verification-error (commit commit-id)
                                                    (signature signature)
                                                    (keyring keyring))
                     (&message
                      (message (format #f (G_ "signature verification failed \
for commit ~a")
                                       (oid->string commit-id)))))))
            ('missing-key
             (raise (condition
                     (&missing-key-error (commit commit-id)
                                         (signature signature))
                     (&message
                      (message (format #f (G_ "could not authenticate \
commit ~a: key ~a is missing")
                                       (oid->string commit-id)
                                       (openpgp-format-fingerprint data)))))))
            ('good-signature data)))))))

(define (read-authorizations port)
  "Read authorizations in the '.guix-authorizations' format from PORT, and
return a list of authorized fingerprints."
  (match (read port)
    (('authorizations ('version 0)
                      (((? string? fingerprints) _ ...) ...)
                      _ ...)
     (map (lambda (fingerprint)
            (base16-string->bytevector
             (string-downcase (string-filter char-set:graphic fingerprint))))
          fingerprints))))

(define* (commit-authorized-keys repository commit
                                 #:optional (default-authorizations '()))
  "Return the list of OpenPGP fingerprints authorized to sign COMMIT, based on
authorizations listed in its parent commits.  If one of the parent commits
does not specify anything, fall back to DEFAULT-AUTHORIZATIONS."
  (define (parents-have-authorizations-file? commit)
    ;; Return true if at least one of the parents of COMMIT has the
    ;; '.guix-authorizations' file.
    (find (lambda (commit)
            (false-if-git-not-found
             (tree-entry-bypath (commit-tree commit)
                                ".guix-authorizations")))
          (commit-parents commit)))

  (define (assert-parents-lack-authorizations commit)
    ;; If COMMIT removes the '.guix-authorizations' file found in one of its
    ;; parents, raise an error.
    (when (parents-have-authorizations-file? commit)
      (raise (condition
              (&unauthorized-commit-error (commit (commit-id commit))
                                          (signing-key #f))
              (&message
               (message (format #f (G_ "commit ~a attempts \
to remove '.guix-authorizations' file")
                                (oid->string (commit-id commit)))))))))

  (define (commit-authorizations commit)
    (catch 'git-error
      (lambda ()
        (let* ((tree  (commit-tree commit))
               (entry (tree-entry-bypath tree ".guix-authorizations"))
               (blob  (blob-lookup repository (tree-entry-id entry))))
          (read-authorizations
           (open-bytevector-input-port (blob-content blob)))))
      (lambda (key error)
        (if (= (git-error-code error) GIT_ENOTFOUND)
            (begin
              ;; Prevent removal of '.guix-authorizations' since it would make
              ;; it trivial to force a fallback to DEFAULT-AUTHORIZATIONS.
              (assert-parents-lack-authorizations commit)
              default-authorizations)
            (throw key error)))))

  (match (commit-parents commit)
    (() default-authorizations)
    (parents
     (apply lset-intersection bytevector=?
            (map commit-authorizations parents)))))

(define* (authenticate-commit repository commit keyring
                              #:key (default-authorizations '()))
  "Authenticate COMMIT from REPOSITORY and return the signing key fingerprint.
Raise an error when authentication fails.  If one of the parent commits does
not specify anything, fall back to DEFAULT-AUTHORIZATIONS."
  (define id
    (commit-id commit))

  (define recent-commit?
    (false-if-git-not-found
     (tree-entry-bypath (commit-tree commit) ".guix-authorizations")))

  (define signing-key
    (commit-signing-key repository id keyring
                        ;; Reject SHA1 signatures unconditionally as suggested
                        ;; by the authors of "SHA-1 is a Shambles" (2019).
                        ;; Accept it for "historical" commits (there are such
                        ;; signatures from April 2020 in the repository).
                        #:disallowed-hash-algorithms
                        (if recent-commit? '(sha1) '())))

  (unless (member (openpgp-public-key-fingerprint signing-key)
                  (commit-authorized-keys repository commit
                                          default-authorizations))
    (raise (condition
            (&unauthorized-commit-error (commit id)
                                        (signing-key signing-key))
            (&message
             (message (format #f (G_ "commit ~a not signed by an authorized \
key: ~a")
                              (oid->string id)
                              (openpgp-format-fingerprint
                               (openpgp-public-key-fingerprint
                                signing-key))))))))

  signing-key)

(define (load-keyring-from-blob repository oid keyring)
  "Augment KEYRING with the keyring available in the blob at OID, which may or
may not be ASCII-armored."
  (let* ((blob (blob-lookup repository oid))
         (port (open-bytevector-input-port (blob-content blob))))
    (get-openpgp-keyring (if (port-ascii-armored? port)
                             (open-bytevector-input-port (read-radix-64 port))
                             port)
                         keyring)))

(define (load-keyring-from-reference repository reference)
  "Load the '.key' files from the tree at REFERENCE in REPOSITORY and return
an OpenPGP keyring."
  (let* ((reference (branch-lookup repository reference BRANCH-ALL))
         (target    (reference-target reference))
         (commit    (commit-lookup repository target))
         (tree      (commit-tree commit)))
    (fold (lambda (name keyring)
            (if (string-suffix? ".key" name)
                (let ((entry (tree-entry-bypath tree name)))
                  (load-keyring-from-blob repository
                                          (tree-entry-id entry)
                                          keyring))
                keyring))
          %empty-keyring
          (tree-list tree))))

(define* (authenticate-commits repository commits
                               #:key
                               (default-authorizations '())
                               (keyring-reference "keyring")
                               (keyring (load-keyring-from-reference
                                         repository keyring-reference))
                               (report-progress (const #t)))
  "Authenticate COMMITS, a list of commit objects, calling REPORT-PROGRESS for
each of them.  Return an alist showing the number of occurrences of each key.
If KEYRING is omitted, the OpenPGP keyring is loaded from KEYRING-REFERENCE in
REPOSITORY."
  (fold (lambda (commit stats)
          (report-progress)
          (let ((signer (authenticate-commit repository commit keyring
                                             #:default-authorizations
                                             default-authorizations)))
            (match (assq signer stats)
              (#f          (cons `(,signer . 1) stats))
              ((_ . count) (cons `(,signer . ,(+ count 1))
                                 (alist-delete signer stats))))))
        '()
        commits))

\f
;;;
;;; Caching.
;;;

(define (authenticated-commit-cache-file key)
  "Return the name of the file that contains the cache of
previously-authenticated commits for KEY."
  (string-append (cache-directory) "/authentication/" key))

(define (previously-authenticated-commits key)
  "Return the previously-authenticated commits under KEY as a list of commit
IDs (hex strings)."
  (catch 'system-error
    (lambda ()
      (call-with-input-file (authenticated-commit-cache-file key)
        (lambda (port)
          ;; If PORT has the wrong permissions, it might have been tampered
          ;; with by another user so ignore its contents.
          (if (= #o600 (stat:perms (stat port)))
              (read port)
              (begin
                (chmod port #o600)
                '())))))
    (lambda args
      (if (= ENOENT (system-error-errno args))
          '()
          (apply throw args)))))

(define (cache-authenticated-commit key commit-id)
  "Record in ~/.cache, under KEY, COMMIT-ID and its closure as
authenticated (only COMMIT-ID is written to cache, though)."
  (define %max-cache-length
    ;; Maximum number of commits in cache.
    200)

  (let ((lst  (delete-duplicates
               (cons commit-id (previously-authenticated-commits key))))
        (file (authenticated-commit-cache-file key)))
    (mkdir-p (dirname file))
    (with-atomic-file-output file
      (lambda (port)
        (let ((lst (if (> (length lst) %max-cache-length)
                       (take lst %max-cache-length) ;truncate
                       lst)))
          (chmod port #o600)
          (display ";; List of previously-authenticated commits.\n\n"
                   port)
          (pretty-print lst port))))))

\f
;;;
;;; High-level interface.
;;;

(define (repository-cache-key repository)
  "Return a unique key to store the authenticate commit cache for REPOSITORY."
  (string-append "checkouts/"
                 (base64-encode
                  (sha256 (string->utf8 (repository-directory repository))))))

(define (verify-introductory-commit repository keyring commit expected-signer)
  "Look up COMMIT in REPOSITORY, and raise an exception if it is not signed by
EXPECTED-SIGNER."
  (define actual-signer
    (openpgp-public-key-fingerprint
     (commit-signing-key repository (commit-id commit) keyring)))

  (unless (bytevector=? expected-signer actual-signer)
    (raise (condition
            (&message
             (message (format #f (G_ "initial commit ~a is signed by '~a' \
instead of '~a'")
                              (oid->string (commit-id commit))
                              (openpgp-format-fingerprint actual-signer)
                              (openpgp-format-fingerprint expected-signer))))))))

(define* (authenticate-repository repository start signer
                                  #:key
                                  (keyring-reference "keyring")
                                  (cache-key (repository-cache-key repository))
                                  (end (reference-target
                                        (repository-head repository)))
                                  (historical-authorizations '())
                                  (make-reporter
                                   (const progress-reporter/silent)))
  "Authenticate REPOSITORY up to commit END, an OID.  Authentication starts
with commit START, an OID, which must be signed by SIGNER; an exception is
raised if that is not the case.  Return an alist mapping OpenPGP public keys
to the number of commits signed by that key that have been traversed.

The OpenPGP keyring is loaded from KEYRING-REFERENCE in REPOSITORY, where
KEYRING-REFERENCE is the name of a branch.  The list of authenticated commits
is cached in the authentication cache under CACHE-KEY.

HISTORICAL-AUTHORIZATIONS must be a list of OpenPGP fingerprints (bytevectors)
denoting the authorized keys for commits whose parent lack the
'.guix-authorizations' file."
  (define start-commit
    (commit-lookup repository start))
  (define end-commit
    (commit-lookup repository end))

  (define keyring
    (load-keyring-from-reference repository keyring-reference))

  (define authenticated-commits
    ;; Previously-authenticated commits that don't need to be checked again.
    (filter-map (lambda (id)
                  (false-if-git-not-found
                   (commit-lookup repository (string->oid id))))
                (previously-authenticated-commits cache-key)))

  (define commits
    ;; Commits to authenticate, excluding the closure of
    ;; AUTHENTICATED-COMMITS.
    (commit-difference end-commit start-commit
                       authenticated-commits))

  ;; When COMMITS is empty, it's because END-COMMIT is in the closure of
  ;; START-COMMIT and/or AUTHENTICATED-COMMITS, in which case it's known to
  ;; be authentic already.
  (if (null? commits)
      '()
      (let ((reporter (make-reporter start-commit end-commit commits)))
        ;; If it's our first time, verify START-COMMIT's signature.
        (when (null? authenticated-commits)
          (verify-introductory-commit repository keyring
                                      start-commit signer))

        (let ((stats (call-with-progress-reporter reporter
                       (lambda (report)
                         (authenticate-commits repository commits
                                               #:keyring keyring
                                               #:default-authorizations
                                               historical-authorizations
                                               #:report-progress report)))))
          (cache-authenticated-commit cache-key
                                      (oid->string (commit-id end-commit)))

          stats))))
Commit	Line	Data
41f443c9 LC	1	;;; GNU Guix --- Functional package management for GNU
	2	;;; Copyright © 2019, 2020 Ludovic Courtès <ludo@gnu.org>
	3	;;;
	4	;;; This file is part of GNU Guix.
	5	;;;
	6	;;; GNU Guix is free software; you can redistribute it and/or modify it
	7	;;; under the terms of the GNU General Public License as published by
	8	;;; the Free Software Foundation; either version 3 of the License, or (at
	9	;;; your option) any later version.
	10	;;;
	11	;;; GNU Guix is distributed in the hope that it will be useful, but
	12	;;; WITHOUT ANY WARRANTY; without even the implied warranty of
	13	;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	14	;;; GNU General Public License for more details.
	15	;;;
	16	;;; You should have received a copy of the GNU General Public License
	17	;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
	18
	19	(define-module (guix git-authenticate)
	20	#:use-module (git)
838f2bdf	21	#:autoload (gcrypt hash) (sha256)
41f443c9	22	#:use-module (guix base16)
838f2bdf LC	23	#:autoload (guix base64) (base64-encode)
	24	#:use-module ((guix git)
	25	#:select (commit-difference false-if-git-not-found))
41f443c9 LC	26	#:use-module (guix i18n)
	27	#:use-module (guix openpgp)
	28	#:use-module ((guix utils)
	29	#:select (cache-directory with-atomic-file-output))
	30	#:use-module ((guix build utils)
	31	#:select (mkdir-p))
838f2bdf	32	#:use-module (guix progress)
41f443c9 LC	33	#:use-module (srfi srfi-1)
	34	#:use-module (srfi srfi-11)
	35	#:use-module (srfi srfi-26)
	36	#:use-module (srfi srfi-34)
	37	#:use-module (srfi srfi-35)
	38	#:use-module (rnrs bytevectors)
	39	#:use-module (rnrs io ports)
	40	#:use-module (ice-9 match)
	41	#:autoload (ice-9 pretty-print) (pretty-print)
	42	#:export (read-authorizations
	43	commit-signing-key
	44	commit-authorized-keys
	45	authenticate-commit
	46	authenticate-commits
	47	load-keyring-from-reference
	48	previously-authenticated-commits
f8213f1b LC	49	cache-authenticated-commit
f8213f1b LC	50
838f2bdf LC	51	repository-cache-key
	52	authenticate-repository
	53
f8213f1b LC	54	git-authentication-error?
	55	git-authentication-error-commit
	56	unsigned-commit-error?
	57	unauthorized-commit-error?
	58	unauthorized-commit-error-signing-key
	59	signature-verification-error?
	60	signature-verification-error-keyring
	61	signature-verification-error-signature
	62	missing-key-error?
	63	missing-key-error-signature))
41f443c9 LC	64
	65	;;; Commentary:
	66	;;;
	67	;;; This module provides tools to authenticate a range of Git commits. A
	68	;;; commit is considered "authentic" if and only if it is signed by an
	69	;;; authorized party. Parties authorized to sign a commit are listed in the
	70	;;; '.guix-authorizations' file of the parent commit.
	71	;;;
	72	;;; Code:
	73
f8213f1b LC	74	(define-condition-type &git-authentication-error &error
	75	git-authentication-error?
	76	(commit git-authentication-error-commit))
	77
	78	(define-condition-type &unsigned-commit-error &git-authentication-error
	79	unsigned-commit-error?)
	80
	81	(define-condition-type &unauthorized-commit-error &git-authentication-error
	82	unauthorized-commit-error?
	83	(signing-key unauthorized-commit-error-signing-key))
	84
	85	(define-condition-type &signature-verification-error &git-authentication-error
	86	signature-verification-error?
	87	(signature signature-verification-error-signature)
	88	(keyring signature-verification-error-keyring))
	89
	90	(define-condition-type &missing-key-error &git-authentication-error
	91	missing-key-error?
	92	(signature missing-key-error-signature))
	93
	94
52c529ff LC	95	(define* (commit-signing-key repo commit-id keyring
52c529ff LC	96	#:key (disallowed-hash-algorithms '(sha1)))
41f443c9	97	"Return the OpenPGP key that signed COMMIT-ID (an OID). Raise an exception
52c529ff LC	98	if the commit is unsigned, has an invalid signature, has a signature using one
52c529ff LC	99	of the hash algorithms in DISALLOWED-HASH-ALGORITHMS, or if its signing key is
41f443c9 LC	100	not in KEYRING."
	101	(let-values (((signature signed-data)
	102	(catch 'git-error
	103	(lambda ()
	104	(commit-extract-signature repo commit-id))
	105	(lambda _
	106	(values #f #f)))))
	107	(unless signature
	108	(raise (condition
f8213f1b	109	(&unsigned-commit-error (commit commit-id))
41f443c9 LC	110	(&message
41f443c9 LC	111	(message (format #f (G_ "commit ~a lacks a signature")
f8213f1b	112	(oid->string commit-id)))))))
41f443c9 LC	113
41f443c9 LC	114	(let ((signature (string->openpgp-packet signature)))
52c529ff LC	115	(when (memq (openpgp-signature-hash-algorithm signature)
	116	`(,@disallowed-hash-algorithms md5))
	117	(raise (condition
	118	(&unsigned-commit-error (commit commit-id))
	119	(&message
	120	(message (format #f (G_ "commit ~a has a ~a signature, \
	121	which is not permitted")
	122	(oid->string commit-id)
	123	(openpgp-signature-hash-algorithm
	124	signature)))))))
	125
41f443c9 LC	126	(with-fluids ((%default-port-encoding "UTF-8"))
	127	(let-values (((status data)
	128	(verify-openpgp-signature signature keyring
	129	(open-input-string signed-data))))
	130	(match status
	131	('bad-signature
	132	;; There's a signature but it's invalid.
	133	(raise (condition
f8213f1b LC	134	(&signature-verification-error (commit commit-id)
	135	(signature signature)
	136	(keyring keyring))
41f443c9 LC	137	(&message
	138	(message (format #f (G_ "signature verification failed \
	139	for commit ~a")
	140	(oid->string commit-id)))))))
	141	('missing-key
	142	(raise (condition
f8213f1b LC	143	(&missing-key-error (commit commit-id)
f8213f1b LC	144	(signature signature))
41f443c9 LC	145	(&message
	146	(message (format #f (G_ "could not authenticate \
	147	commit ~a: key ~a is missing")
	148	(oid->string commit-id)
b3679394	149	(openpgp-format-fingerprint data)))))))
41f443c9 LC	150	('good-signature data)))))))
	151
	152	(define (read-authorizations port)
	153	"Read authorizations in the '.guix-authorizations' format from PORT, and
	154	return a list of authorized fingerprints."
	155	(match (read port)
	156	(('authorizations ('version 0)
	157	(((? string? fingerprints) _ ...) ...)
	158	_ ...)
	159	(map (lambda (fingerprint)
	160	(base16-string->bytevector
	161	(string-downcase (string-filter char-set:graphic fingerprint))))
	162	fingerprints))))
	163
	164	(define* (commit-authorized-keys repository commit
	165	#:optional (default-authorizations '()))
	166	"Return the list of OpenPGP fingerprints authorized to sign COMMIT, based on
	167	authorizations listed in its parent commits. If one of the parent commits
	168	does not specify anything, fall back to DEFAULT-AUTHORIZATIONS."
e7827560 LC	169	(define (parents-have-authorizations-file? commit)
	170	;; Return true if at least one of the parents of COMMIT has the
	171	;; '.guix-authorizations' file.
	172	(find (lambda (commit)
	173	(false-if-git-not-found
	174	(tree-entry-bypath (commit-tree commit)
	175	".guix-authorizations")))
	176	(commit-parents commit)))
	177
	178	(define (assert-parents-lack-authorizations commit)
	179	;; If COMMIT removes the '.guix-authorizations' file found in one of its
	180	;; parents, raise an error.
	181	(when (parents-have-authorizations-file? commit)
	182	(raise (condition
	183	(&unauthorized-commit-error (commit (commit-id commit))
	184	(signing-key #f))
	185	(&message
	186	(message (format #f (G_ "commit ~a attempts \
	187	to remove '.guix-authorizations' file")
	188	(oid->string (commit-id commit)))))))))
	189
41f443c9 LC	190	(define (commit-authorizations commit)
	191	(catch 'git-error
	192	(lambda ()
	193	(let* ((tree (commit-tree commit))
	194	(entry (tree-entry-bypath tree ".guix-authorizations"))
	195	(blob (blob-lookup repository (tree-entry-id entry))))
	196	(read-authorizations
	197	(open-bytevector-input-port (blob-content blob)))))
	198	(lambda (key error)
	199	(if (= (git-error-code error) GIT_ENOTFOUND)
e7827560 LC	200	(begin
	201	;; Prevent removal of '.guix-authorizations' since it would make
	202	;; it trivial to force a fallback to DEFAULT-AUTHORIZATIONS.
	203	(assert-parents-lack-authorizations commit)
	204	default-authorizations)
41f443c9 LC	205	(throw key error)))))
41f443c9 LC	206
eef859e8 LC	207	(match (commit-parents commit)
	208	(() default-authorizations)
	209	(parents
	210	(apply lset-intersection bytevector=?
	211	(map commit-authorizations parents)))))
41f443c9 LC	212
	213	(define* (authenticate-commit repository commit keyring
	214	#:key (default-authorizations '()))
	215	"Authenticate COMMIT from REPOSITORY and return the signing key fingerprint.
	216	Raise an error when authentication fails. If one of the parent commits does
	217	not specify anything, fall back to DEFAULT-AUTHORIZATIONS."
	218	(define id
	219	(commit-id commit))
	220
52c529ff LC	221	(define recent-commit?
	222	(false-if-git-not-found
	223	(tree-entry-bypath (commit-tree commit) ".guix-authorizations")))
	224
41f443c9	225	(define signing-key
52c529ff LC	226	(commit-signing-key repository id keyring
	227	;; Reject SHA1 signatures unconditionally as suggested
	228	;; by the authors of "SHA-1 is a Shambles" (2019).
	229	;; Accept it for "historical" commits (there are such
	230	;; signatures from April 2020 in the repository).
	231	#:disallowed-hash-algorithms
	232	(if recent-commit? '(sha1) '())))
41f443c9 LC	233
	234	(unless (member (openpgp-public-key-fingerprint signing-key)
	235	(commit-authorized-keys repository commit
	236	default-authorizations))
	237	(raise (condition
f8213f1b LC	238	(&unauthorized-commit-error (commit id)
f8213f1b LC	239	(signing-key signing-key))
41f443c9 LC	240	(&message
	241	(message (format #f (G_ "commit ~a not signed by an authorized \
	242	key: ~a")
	243	(oid->string id)
	244	(openpgp-format-fingerprint
	245	(openpgp-public-key-fingerprint
	246	signing-key))))))))
	247
	248	signing-key)
	249
	250	(define (load-keyring-from-blob repository oid keyring)
	251	"Augment KEYRING with the keyring available in the blob at OID, which may or
	252	may not be ASCII-armored."
	253	(let* ((blob (blob-lookup repository oid))
	254	(port (open-bytevector-input-port (blob-content blob))))
	255	(get-openpgp-keyring (if (port-ascii-armored? port)
	256	(open-bytevector-input-port (read-radix-64 port))
	257	port)
	258	keyring)))
	259
	260	(define (load-keyring-from-reference repository reference)
	261	"Load the '.key' files from the tree at REFERENCE in REPOSITORY and return
	262	an OpenPGP keyring."
512b9e2d	263	(let* ((reference (branch-lookup repository reference BRANCH-ALL))
41f443c9 LC	264	(target (reference-target reference))
	265	(commit (commit-lookup repository target))
	266	(tree (commit-tree commit)))
	267	(fold (lambda (name keyring)
	268	(if (string-suffix? ".key" name)
	269	(let ((entry (tree-entry-bypath tree name)))
	270	(load-keyring-from-blob repository
	271	(tree-entry-id entry)
	272	keyring))
	273	keyring))
	274	%empty-keyring
	275	(tree-list tree))))
	276
	277	(define* (authenticate-commits repository commits
	278	#:key
	279	(default-authorizations '())
	280	(keyring-reference "keyring")
41946b79 LC	281	(keyring (load-keyring-from-reference
41946b79 LC	282	repository keyring-reference))
41f443c9 LC	283	(report-progress (const #t)))
	284	"Authenticate COMMITS, a list of commit objects, calling REPORT-PROGRESS for
	285	each of them. Return an alist showing the number of occurrences of each key.
41946b79 LC	286	If KEYRING is omitted, the OpenPGP keyring is loaded from KEYRING-REFERENCE in
41946b79 LC	287	REPOSITORY."
41f443c9 LC	288	(fold (lambda (commit stats)
	289	(report-progress)
	290	(let ((signer (authenticate-commit repository commit keyring
	291	#:default-authorizations
	292	default-authorizations)))
	293	(match (assq signer stats)
	294	(#f (cons `(,signer . 1) stats))
	295	((_ . count) (cons `(,signer . ,(+ count 1))
	296	(alist-delete signer stats))))))
	297	'()
	298	commits))
	299
	300	\f
	301	;;;
	302	;;; Caching.
	303	;;;
	304
a450b434	305	(define (authenticated-commit-cache-file key)
41f443c9	306	"Return the name of the file that contains the cache of
a450b434 LC	307	previously-authenticated commits for KEY."
a450b434 LC	308	(string-append (cache-directory) "/authentication/" key))
41f443c9	309
a450b434 LC	310	(define (previously-authenticated-commits key)
	311	"Return the previously-authenticated commits under KEY as a list of commit
	312	IDs (hex strings)."
41f443c9 LC	313	(catch 'system-error
41f443c9 LC	314	(lambda ()
a450b434	315	(call-with-input-file (authenticated-commit-cache-file key)
41939c37 LC	316	(lambda (port)
	317	;; If PORT has the wrong permissions, it might have been tampered
	318	;; with by another user so ignore its contents.
	319	(if (= #o600 (stat:perms (stat port)))
	320	(read port)
	321	(begin
	322	(chmod port #o600)
	323	'())))))
41f443c9 LC	324	(lambda args
	325	(if (= ENOENT (system-error-errno args))
	326	'()
	327	(apply throw args)))))
	328
a450b434 LC	329	(define (cache-authenticated-commit key commit-id)
	330	"Record in ~/.cache, under KEY, COMMIT-ID and its closure as
	331	authenticated (only COMMIT-ID is written to cache, though)."
41f443c9 LC	332	(define %max-cache-length
	333	;; Maximum number of commits in cache.
	334	200)
	335
	336	(let ((lst (delete-duplicates
a450b434 LC	337	(cons commit-id (previously-authenticated-commits key))))
a450b434 LC	338	(file (authenticated-commit-cache-file key)))
41f443c9 LC	339	(mkdir-p (dirname file))
	340	(with-atomic-file-output file
	341	(lambda (port)
	342	(let ((lst (if (> (length lst) %max-cache-length)
	343	(take lst %max-cache-length) ;truncate
	344	lst)))
	345	(chmod port #o600)
	346	(display ";; List of previously-authenticated commits.\n\n"
	347	port)
	348	(pretty-print lst port))))))
838f2bdf LC	349
	350	\f
	351	;;;
	352	;;; High-level interface.
	353	;;;
	354
	355	(define (repository-cache-key repository)
	356	"Return a unique key to store the authenticate commit cache for REPOSITORY."
	357	(string-append "checkouts/"
	358	(base64-encode
	359	(sha256 (string->utf8 (repository-directory repository))))))
	360
	361	(define (verify-introductory-commit repository keyring commit expected-signer)
	362	"Look up COMMIT in REPOSITORY, and raise an exception if it is not signed by
	363	EXPECTED-SIGNER."
	364	(define actual-signer
	365	(openpgp-public-key-fingerprint
	366	(commit-signing-key repository (commit-id commit) keyring)))
	367
	368	(unless (bytevector=? expected-signer actual-signer)
	369	(raise (condition
	370	(&message
	371	(message (format #f (G_ "initial commit ~a is signed by '~a' \
	372	instead of '~a'")
	373	(oid->string (commit-id commit))
	374	(openpgp-format-fingerprint actual-signer)
	375	(openpgp-format-fingerprint expected-signer))))))))
	376
	377	(define* (authenticate-repository repository start signer
	378	#:key
	379	(keyring-reference "keyring")
	380	(cache-key (repository-cache-key repository))
	381	(end (reference-target
	382	(repository-head repository)))
	383	(historical-authorizations '())
	384	(make-reporter
	385	(const progress-reporter/silent)))
	386	"Authenticate REPOSITORY up to commit END, an OID. Authentication starts
	387	with commit START, an OID, which must be signed by SIGNER; an exception is
	388	raised if that is not the case. Return an alist mapping OpenPGP public keys
	389	to the number of commits signed by that key that have been traversed.
	390
	391	The OpenPGP keyring is loaded from KEYRING-REFERENCE in REPOSITORY, where
	392	KEYRING-REFERENCE is the name of a branch. The list of authenticated commits
	393	is cached in the authentication cache under CACHE-KEY.
	394
	395	HISTORICAL-AUTHORIZATIONS must be a list of OpenPGP fingerprints (bytevectors)
	396	denoting the authorized keys for commits whose parent lack the
	397	'.guix-authorizations' file."
	398	(define start-commit
	399	(commit-lookup repository start))
	400	(define end-commit
	401	(commit-lookup repository end))
	402
	403	(define keyring
	404	(load-keyring-from-reference repository keyring-reference))
	405
	406	(define authenticated-commits
	407	;; Previously-authenticated commits that don't need to be checked again.
	408	(filter-map (lambda (id)
	409	(false-if-git-not-found
	410	(commit-lookup repository (string->oid id))))
	411	(previously-authenticated-commits cache-key)))
	412
413	(define commits
414	;; Commits to authenticate, excluding the closure of
415	;; AUTHENTICATED-COMMITS.
416	(commit-difference end-commit start-commit
417	authenticated-commits))
418
419	;; When COMMITS is empty, it's because END-COMMIT is in the closure of
420	;; START-COMMIT and/or AUTHENTICATED-COMMITS, in which case it's known to
421	;; be authentic already.
422	(if (null? commits)
423	'()
424	(let ((reporter (make-reporter start-commit end-commit commits)))
425	;; If it's our first time, verify START-COMMIT's signature.
426	(when (null? authenticated-commits)
427	(verify-introductory-commit repository keyring
428	start-commit signer))
429
430	(let ((stats (call-with-progress-reporter reporter
431	(lambda (report)
432	(authenticate-commits repository commits
433	#:keyring keyring
434	#:default-authorizations
435	historical-authorizations
436	#:report-progress report)))))
437	(cache-authenticated-commit cache-key
438	(oid->string (commit-id end-commit)))
439
440	stats))))