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pull: Protect against downgrade attacks. 

* guix/scripts/pull.scm (%default-options): Add 'validate-pull'.
(%options, show-help): Add '--allow-downgrades'.
(warn-about-backward-updates): New procedure.
(guix-pull): Pass #:current-channels and #:validate-pull to
'latest-channel-instances'.
* guix/channels.scm (ensure-forward-channel-update): Add hint for
when (channel-commit channel) is true.
* doc/guix.texi (Invoking guix pull): Document '--allow-downgrades'.
This commit is contained in:
Ludovic Courtès 2020-05-20 23:18:09 +02:00
parent 872898f768
commit 9744cc7b46
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3 changed files with 66 additions and 18 deletions
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15
doc/guix.texi
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@ -3900,6 +3900,21 @@ Use @var{profile} instead of @file{~/.config/guix/current}.
Show which channel commit(s) would be used and what would be built or
substituted but do not actually do it.
@item --allow-downgrades
Allow pulling older or unrelated revisions of channels than those
currently in use.
@cindex downgrade attacks, protection against
By default, @command{guix pull} protects against so-called ``downgrade
attacks'' whereby the Git repository of a channel would be reset to an
earlier or unrelated revision of itself, potentially leading you to
install older, known-vulnerable versions of software packages.
@quotation Note
Make sure you understand its security implications before using
@option{--allow-downgrades}.
@end quotation
@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of

34
guix/channels.scm
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@ -246,25 +246,29 @@ This procedure implements a channel update policy meant to be used as a
('ancestor #t)
('self #t)
(_
(raise (apply make-compound-condition
(condition
(&message (message
(format #f (G_ "\
(raise (make-compound-condition
(condition
(&message (message
(format #f (G_ "\
aborting update of channel '~a' to commit ~a, which is not a descendant of ~a")
(channel-name channel)
(channel-instance-commit instance)
start))))
(channel-name channel)
(channel-instance-commit instance)
start))))
;; Don't show the hint when the user explicitly specified a
;; commit in CHANNEL.
(if (channel-commit channel)
'()
(list (condition
(&fix-hint
(hint (G_ "This could indicate that the channel has
;; If the user asked for a specific commit, they might want
;; that to happen nevertheless, so tell them about the
;; relevant 'guix pull' option.
(if (channel-commit channel)
(condition
(&fix-hint
(hint (G_ "Use @option{--allow-downgrades} to force
this downgrade."))))
(condition
(&fix-hint
(hint (G_ "This could indicate that the channel has
been tampered with and is trying to force a roll-back, preventing you from
getting the latest updates. If you think this is not the case, explicitly
allow non-forward updates.")))))))))))
allow non-forward updates."))))))))))
(define* (latest-channel-instances store channels
#:key

35
guix/scripts/pull.scm
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@ -81,7 +81,8 @@
(multiplexed-build-output? . #t)
(graft? . #t)
(debug . 0)
(verbosity . 1)))
(verbosity . 1)
(validate-pull . ,ensure-forward-channel-update)))
(define (show-help)
(display (G_ "Usage: guix pull [OPTION]...
@ -94,6 +95,8 @@ Download and deploy the latest version of Guix.\n"))
--commit=COMMIT download the specified COMMIT"))
(display (G_ "
--branch=BRANCH download the tip of the specified BRANCH"))
(display (G_ "
--allow-downgrades allow downgrades to earlier channel revisions"))
(display (G_ "
-N, --news display news compared to the previous generation"))
(display (G_ "
@ -158,6 +161,10 @@ Download and deploy the latest version of Guix.\n"))
(option '("branch") #t #f
(lambda (opt name arg result)
(alist-cons 'ref `(branch . ,arg) result)))
(option '("allow-downgrades") #f #f
(lambda (opt name arg result)
(alist-cons 'validate-pull warn-about-backward-updates
result)))
(option '(#\p "profile") #t #f
(lambda (opt name arg result)
(alist-cons 'profile (canonicalize-profile arg)
@ -188,6 +195,21 @@ Download and deploy the latest version of Guix.\n"))
%standard-build-options))
(define (warn-about-backward-updates channel start instance relation)
"Warn about non-forward updates of CHANNEL from START to INSTANCE, without
aborting."
(match relation
((or 'ancestor 'self)
#t)
('descendant
(warning (G_ "rolling back channel '~a' from ~a to ~a~%")
(channel-name channel) start
(channel-instance-commit instance)))
('unrelated
(warning (G_ "moving channel '~a' from ~a to unrelated commit ~a~%")
(channel-name channel) start
(channel-instance-commit instance)))))
(define* (display-profile-news profile #:key concise?
current-is-newer?)
"Display what's up in PROFILE--new packages, and all that. If
@ -749,7 +771,9 @@ Use '~/.config/guix/channels.scm' instead."))
(substitutes? (assoc-ref opts 'substitutes?))
(dry-run? (assoc-ref opts 'dry-run?))
(channels (channel-list opts))
(profile (or (assoc-ref opts 'profile) %current-profile)))
(profile (or (assoc-ref opts 'profile) %current-profile))
(current-channels (profile-channels profile))
(validate-pull (assoc-ref opts 'validate-pull)))
(cond ((assoc-ref opts 'query)
(process-query opts profile))
((assoc-ref opts 'generation)
@ -766,7 +790,12 @@ Use '~/.config/guix/channels.scm' instead."))
(ensure-default-profile)
(honor-x509-certificates store)
(let ((instances (latest-channel-instances store channels)))
(let ((instances
(latest-channel-instances store channels
#:current-channels
current-channels
#:validate-pull
validate-pull)))
(format (current-error-port)
(N_ "Building from this channel:~%"
"Building from these channels:~%"