Support package checksum verification

Package checksum verification is the first step towards protecting
users of package.el against replay attacks.  Signing individual
packages still allows a hostile actor to distribute an out-of-date
package containing a known security defect.  To avoid that, we need to
distribute signed package metadata (the ELPA "archive-contents" file)
and checksums for the individual packages together.  (Bug#19479)

A subsequent patch will add support for last-update and expiration
timestamps in "archive-contents", without which the protection against
replay attacks will be largely ineffective.

Taken together, this feature will make signing individual packages
obsolete.  We will instead rely on signing the metadata, package
checksums and timestamps.  Note that individual package signatures
should still be distributed for a long time still to support old
versions of Emacs.

For more on replay attacks, see:
https://www2.cs.arizona.edu/stork/packagemanagersecurity/attacks-on-package-managers.html

* lisp/emacs-lisp/package.el (package-verify-checksums): New
defcustom.
(package-desc, package--ac-desc)
(package--add-to-archive-contents, package-install-from-archive): New
fields 'size' and 'checksums'.
(package-desc-filename): New function.

(package-error): New error type.
(bad-signature): Inherit from error type 'package-error'.
(bad-checksum, bad-size): New error types.
(package-insecure-hash-algorithms): New constant.
(package--verify-package-checksum)
(package--verify-package-size): New function to verify that the
checksum and size of a package corresponds to the checksum and size
data in the "archive-contents" file on the package archive.
(package--show-verify-checksum-error): New function to show
details of an error on checksum verification.

* lisp/emacs-lisp/package-x.el (package-upload-buffer-internal):
Update to use above new fields 'size' and 'checksums'.

* test/lisp/emacs-lisp/package-tests.el (package-test-refresh-contents)
(package-test-install-single-from-archive)
(package-test-list-filter-by-archive)
(package-test-list-filter-by-status): Update tests.
(with-install-using-checksum): New macro.
(package-test-install-wrong-size-single)
(package-test-install-wrong-size-tar): New tests for size checking.
(package-test-install-with-checksum/single-valid)
(package-test-install-with-checksum/single-invalid)
(package-test-install-with-checksum/tar-valid)
(package-test-install-with-checksum/tar-invalid): New tests for
installing packages with checksums.
(package-test-verification-text)
(package-tests-valid-md5-checksum)
(package-tests-valid-sha256-checksum)
(package-tests-valid-sha512-checksum): New variables.
(package-tests--run-verify-checksums-test): New macro.
(package-test-verify-package-checksums-nil/ignore-invalid)
(package-test-verify-package-checksums-allow-missing)
(package-test-verify-package-checksums-allow-missing/missing)
(package-test-verify-package-checksums-allow-missing/ignore-unsupported)
(package-test-verify-package-checksums-t)
(package-test-verify-package-checksums-t/invalid-fails)
(package-test-verify-package-checksums-t/missing-fails)
(package-test-verify-package-checksums-all)
(package-test-verify-package-checksums-all/invalid-fails)
(package-test-verify-package-checksums-all/missing-fails)
(package-test-verify-package-checksums-all/no-supported-hash-fails)
(package-test-verify-package-checksums-all/ignore-unsupported)
(package-test-verify-package-size): New tests for the checksum
support.

* test/lisp/emacs-lisp/package-resources/archive-contents:
* test/lisp/emacs-lisp/package-resources/checksum-invalid-1.0.el:
* test/lisp/emacs-lisp/package-resources/checksum-valid-123.el:
* test/lisp/emacs-lisp/package-resources/checksum-valid-tar-0.99.tar:
* test/lisp/emacs-lisp/package-resources/checksum-valid-tar-0.99.tar:
New test data files.

* doc/emacs/package.texi (Package Installation): Document package
checksum checking.
* etc/NEWS: Announce it.

1 files changed, 196 insertions, 7 deletions

diff --git a/test/lisp/emacs-lisp/package-tests.el b/test/lisp/emacs-lisp/package-tests.el
index 23267545f83..a81506d626b 100644
--- a/test/lisp/emacs-lisp/package-tests.el
+++ b/test/lisp/emacs-lisp/package-tests.el
@@ -44,6 +44,9 @@
 
 (setq package-menu-async nil)
 
+;; Silence byte-compiler.
+(defvar epg-config--program-alist)
+
 (defvar package-test-user-dir nil
   "Directory to use for installing packages during testing.")
 
@@ -304,14 +307,33 @@ Must called from within a `tar-mode' buffer."
   (with-package-test ()
     (package-initialize)
     (package-refresh-contents)
-    (should (eq 4 (length package-archive-contents)))))
+    (should (eq 10 (length package-archive-contents)))))
 
 (ert-deftest package-test-install-single-from-archive ()
   "Install a single package from a package archive."
   (with-package-test ()
     (package-initialize)
     (package-refresh-contents)
-    (package-install 'simple-single)))
+    (package-install 'simple-single)
+    (should (package-installed-p 'simple-single))))
+
+(ert-deftest package-test-install-wrong-size-single ()
+  "Install a tar package with invalid size."
+  (should-error
+   (with-package-test ()
+     (package-initialize)
+     (package-refresh-contents)
+     (package-install 'wrong-size-single))
+   :type 'bad-size))
+
+(ert-deftest package-test-install-wrong-size-tar ()
+  "Install a tar package with invalid size."
+  (should-error
+   (with-package-test ()
+     (package-initialize)
+     (package-refresh-contents)
+     (package-install 'wrong-size-tar))
+   :type 'bad-size))
 
 (ert-deftest package-test-install-prioritized ()
   "Install a lower version from a higher-prioritized archive."
@@ -389,8 +411,8 @@ Must called from within a `tar-mode' buffer."
     ;;       the testing environment currently only has one.
     (package-menu-filter-by-archive "gnu")
     (goto-char (point-min))
-    (should (looking-at "^\\s-+multi-file"))
-    (should (= (count-lines (point-min) (point-max)) 4))
+    (should (looking-at "^\\s-+checksum-invalid"))
+    (should (= (count-lines (point-min) (point-max)) 10))
     (should-error (package-menu-filter-by-archive "non-existent archive"))))
 
 (ert-deftest package-test-list-filter-by-keyword ()
@@ -416,7 +438,7 @@ Must called from within a `tar-mode' buffer."
     (package-menu-filter-by-status "available")
     (goto-char (point-min))
     (should (re-search-forward "^\\s-+multi-file" nil t))
-    (should (= (count-lines (point-min) (point-max)) 4))
+    (should (= (count-lines (point-min) (point-max)) 10))
     ;; No installed packages in default environment.
     (should-error (package-menu-filter-by-status "installed"))))
 
@@ -671,6 +693,169 @@ Must called from within a `tar-mode' buffer."
 		"Status: Installed in ['`‘]signed-good-1.0/['’]."
 		nil t))))))
 
+
+;;; Tests for package checksum verification.
+
+(defmacro with-install-using-checksum (ok fail package)
+  "Test installing PACKAGE while setting `package-verify-checksums'."
+  (declare (indent 2))
+  `(progn
+     (dolist (opt ,ok)
+       (let ((package-verify-checksums opt))
+         (with-package-test ()
+           (package-initialize)
+           (package-refresh-contents)
+           (package-install ,package)
+           (package-installed-p ,package))))
+     (dolist (opt ,fail)
+       (let ((package-verify-checksums opt))
+         (should-error
+          (with-package-test ()
+            (package-initialize)
+            (package-refresh-contents)
+            (package-install ,package))
+          :type 'bad-checksum)))))
+
+(ert-deftest package-test-install-with-checksum/single-valid ()
+  "Install a single package with valid checksum."
+  (with-install-using-checksum '(nil allow-missing t all) '() 'checksum-valid))
+
+(ert-deftest package-test-install-with-checksum/single-invalid ()
+  "Install a tar package with invalid checksum."
+  (with-install-using-checksum '(nil) '(allow-missing t all) 'checksum-invalid))
+
+(ert-deftest package-test-install-with-checksum/tar-valid ()
+  "Install a tar package with valid checksum."
+  (with-install-using-checksum '(nil allow-missing t all) '() 'checksum-valid-tar))
+
+(ert-deftest package-test-install-with-checksum/tar-invalid ()
+  "Install a tar package with invalid checksum."
+  (with-install-using-checksum '(nil) '(allow-missing t all) 'checksum-invalid-tar))
+
+(defconst package-test-verification-text
+  "Example text for testing checksum verification.")
+(defconst package-tests-valid-md5-checksum
+  ;; (secure-hash 'md5 package-test-verification-text)
+  "abe6375809e532f081b808b3aa052dfb")
+(defconst package-tests-valid-sha256-checksum
+  ;; (secure-hash 'sha256 package-test-verification-text)
+  "6875aa4523e45ddef627b4edf1296f1d7dd0c22ddd6a6584f0228215d25eefcd")
+(defconst package-tests-valid-sha512-checksum
+  ;; (secure-hash 'sha512 package-test-verification-text)
+  (concat "bdc631f9e675b1ea34570f0a4bb44568dc5cecac905eea737f5f451bc52fd0c6"
+          "81b0d8b3dc2a942b9950fbe9096ebdf517668245c9b5a7bbdea8487a8f9cdce6"))
+
+(defmacro package-tests--run-verify-checksums-test (verify-checksums checksums)
+  "Run a test for `package-verify-checksums'."
+  (declare (indent 1))
+  `(with-temp-buffer
+     (insert package-test-verification-text)
+     (let ((package-verify-checksums ,verify-checksums)
+           (pkg (package-desc-create :name 'foobar
+                              :version '(1 0)
+                              :summary "Just a package with checksum."
+                              :kind 'single
+                              :checksums ,checksums)))
+       (package--verify-package-checksum pkg))))
+
+(ert-deftest package-test-verify-package-checksums-nil/ignore-invalid ()
+  "Ignore all checksums even when invalid."
+  (package-tests--run-verify-checksums-test nil
+    '((sha512 . "invalid")
+      (invalid . "invalid"))))
+
+(ert-deftest package-test-verify-package-checksums-nil/ignore-empty ()
+  "Ignore all checksums even when empty."
+  (package-tests--run-verify-checksums-test nil
+    nil))
+
+(ert-deftest package-test-verify-package-checksums-allow-missing ()
+  "Verify checksums (allow-missing) -- verify if available."
+  (package-tests--run-verify-checksums-test 'allow-missing
+    `((sha512 . ,package-tests-valid-sha512-checksum))))
+
+(ert-deftest package-test-verify-package-checksums-allow-missing/missing ()
+  "Verify checksums (allow-missing) -- allow missing."
+  (package-tests--run-verify-checksums-test 'allow-missing
+    nil))
+
+(ert-deftest package-test-verify-package-checksums-allow-missing/ignore-unsupported ()
+  "Verify checksums (t) -- ignore unsupported algorithm."
+  (package-tests--run-verify-checksums-test 'allow-missing
+    `((ignore . "not supported")
+      (sha512 . ,package-tests-valid-sha512-checksum))))
+
+(ert-deftest package-test-verify-package-checksums-t ()
+  "Verify checksums (t) -- succeed when valid."
+  (package-tests--run-verify-checksums-test t
+    `((sha512 . ,package-tests-valid-sha512-checksum))))
+
+(ert-deftest package-test-verify-package-checksums-t/invalid-fails ()
+  "Verify checksums (t) -- fail on invalid."
+  (should-error
+   (package-tests--run-verify-checksums-test t
+     '((sha512 . "invalid")))
+   :type 'bad-checksum))
+
+(ert-deftest package-test-verify-package-checksums-t/missing-fails ()
+  "Verify checksums (t) -- fail on missing."
+  (should-error
+   (package-tests--run-verify-checksums-test t
+     nil)
+   :type 'bad-checksum))
+
+(ert-deftest package-test-verify-package-checksums-t/ignore-unsupported ()
+  "Verify checksums (t) -- ignore unsupported algorithm."
+  (package-tests--run-verify-checksums-test t
+    `((ignore . "not supported")
+      (sha512 . ,package-tests-valid-sha512-checksum))))
+
+(ert-deftest package-test-verify-package-checksums-all ()
+  "Verify checksums (all) -- succeed on valid."
+  (package-tests--run-verify-checksums-test 'all
+    `((md5    . ,package-tests-valid-md5-checksum)
+      (sha256 . ,package-tests-valid-sha256-checksum)
+      (sha512 . ,package-tests-valid-sha512-checksum))))
+
+(ert-deftest package-test-verify-package-checksums-all/invalid-fails ()
+  "Verify checksums (all) -- fail if one checksum is invalid."
+  (should-error
+   (package-tests--run-verify-checksums-test 'all
+     `((md5    . ,package-tests-valid-md5-checksum)
+       (sha256 . "invalid")
+       (sha512 . ,package-tests-valid-sha512-checksum)))
+   :type 'bad-checksum))
+
+(ert-deftest package-test-verify-package-checksums-all/missing-fails ()
+  "Verify checksums (all) -- fail on missing checksums."
+  (should-error
+   (package-tests--run-verify-checksums-test 'all
+     nil)
+   :type 'bad-checksum))
+
+(ert-deftest package-test-verify-package-checksums-all/no-supported-hash-fails ()
+  "Verify checksums (all) -- fail if we have no supported hash."
+  (should-error
+   (package-tests--run-verify-checksums-test 'all
+     '((unsupported . "invalid")))
+   :type 'bad-checksum))
+
+(ert-deftest package-test-verify-package-checksums-all/ignore-unsupported ()
+  "Verify checksums (all) -- succed if one hash algorithm is unsupported.
+If the rest succeed, just ignore the unsupported one."
+  (package-tests--run-verify-checksums-test 'all
+    `((md5    . ,package-tests-valid-md5-checksum)
+      (sha256 . ,package-tests-valid-sha256-checksum)
+      (sha512 . ,package-tests-valid-sha512-checksum)
+      (ignore . "not supported"))))
+
+(ert-deftest package-test-verify-package-size ()
+  (with-temp-buffer
+    (let ((pkg-desc (package-desc-create :size 6)))
+      (insert "123456")
+      (package--verify-package-size pkg-desc)
+      (insert "7")
+      (should-error (package--verify-package-size pkg-desc)))))
 
 
 ;;; Tests for package-x features.
@@ -684,7 +869,9 @@ Must called from within a `tar-mode' buffer."
                               'single
                               '((:authors ("J. R. Hacker" . "jrh@example.com"))
                                 (:maintainer "J. R. Hacker" . "jrh@example.com")
-                                (:url . "http://doodles.au"))))
+                                (:url . "http://doodles.au"))
+                              nil
+                              nil))
   "Expected contents of the archive entry from the \"simple-single\" package.")
 
 (defvar package-x-test--single-archive-entry-1-4
@@ -693,7 +880,9 @@ Must called from within a `tar-mode' buffer."
                               "A single-file package with no dependencies"
                               'single
                               '((:authors ("J. R. Hacker" . "jrh@example.com"))
-                                (:maintainer "J. R. Hacker" . "jrh@example.com"))))
+                                (:maintainer "J. R. Hacker" . "jrh@example.com"))
+                              nil
+                              nil))
   "Expected contents of the archive entry from the updated \"simple-single\" package.")
 
 (ert-deftest package-x-test-upload-buffer ()