From: zimoun <zimon.toutoune@gmail.com>
To: "Ludovic Courtès" <ludo@gnu.org>
Cc: 41425@debbugs.gnu.org
Subject: [bug#41425] [PATCH 0/5] Have 'guix pull' protect against downgrade attacks
Date: Thu, 28 May 2020 10:06:07 +0200 [thread overview]
Message-ID: <CAJ3okZ1S6CCD2s3D0Wqmucnb_6Sdu7Sg4A4eVk=AvmGxg2HMEQ@mail.gmail.com> (raw)
In-Reply-To: <87v9khjq3y.fsf@gnu.org>
Hi Ludo,
On Wed, 27 May 2020 at 18:32, Ludovic Courtès <ludo@gnu.org> wrote:
> > (commit-relation left merge)
> > Segmentation fault
>
> It took me a while to notice, but the problem with the code above is
> that ‘repo’ is closed when you call ‘commit-relation’, and thus the
> commit objects are invalid. It works if you keep ‘repo’ alive:
It make totally sense. Thank you for the explanations.
> --8<---------------cut here---------------start------------->8---
> $ guix describe
> Generacio 145 May 25 2020 00:37:58 (nuna)
> guix 9744cc7
> repository URL: https://git.savannah.gnu.org/git/guix.git
> branch: master
> commit: 9744cc7b4636fafb772c94adb8f05961b5b39f16
> $ guix repl
> GNU Guile 3.0.2
> Copyright (C) 1995-2020 Free Software Foundation, Inc.
>
> Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
> This program is free software, and you are welcome to redistribute it
> under certain conditions; type `,show c' for details.
>
> Enter `,help' for help.
> scheme@(guix-user)> (use-modules (guix git) (guix channels) (guix tests git) (git))
> (define url-cache-directory (@@ (guix git) url-cache-directory))
> (define dir (url-cache-directory (channel-url (car %default-channels))))
> ;;; <stdin>:2:0: warning: possibly unused local top-level variable `url-cache-directory'
> ;;; <stdin>:3:0: warning: possibly unused local top-level variable `dir'
> scheme@(guix-user)> (define repo (repository-open dir))
> ;;; <stdin>:4:0: warning: possibly unused local top-level variable `repo'
> scheme@(guix-user)> (define merge (find-commit repo "Merge"))
> ;;; <stdin>:5:0: warning: possibly unused local top-level variable `merge'
> scheme@(guix-user)> merge
> $1 = #<git-commit b4440de133401abc6ce8be6c1c2e720efd9b2ba3>
> scheme@(guix-user)> (define left (car (commit-parents merge)))
> left
> ;;; <stdin>:7:0: warning: possibly unused local top-level variable `left'
> $2 = #<git-commit 141262f266ab702c856f634889d4130ae661e79f>
> scheme@(guix-user)> (commit-relation left merge)
> $3 = ancestor
> scheme@(guix-user)> (gc)
> scheme@(guix-user)> (commit-relation left merge)
> $4 = ancestor
> --8<---------------cut here---------------end--------------->8---
Well, the '(gc)' has no effect here because 'repo' is still alive and
thus the reference too. Instead, an example would be:
--8<---------------cut here---------------start------------->8---
[...]
scheme@(guix-user)> (commit-relation left merge)
$3 = ancestor
scheme@(guix-user)> (define repo 42)
scheme@(guix-user)> (commit-relation left merge)
$4 = ancestor
scheme@(guix-user)> (gc)
scheme@(guix-user)> (commit-relation left merge)
Segmentation fault
--8<---------------cut here---------------end--------------->8---
isn't? Which is somehow the same than the initial example.
> The solution in such cases is to synchronize the object lifetimes. In
> this case, commits would keep a reference to the repository object to
> prevent it from being GC’d, as is done with ‘%submodule-owners’ in (git
> submodule).
I think I understand.
> Could you make an issue over at
> <https://gitlab.com/guile-git/guile-git>?
I will.
Thank you for the explanation.
next prev parent reply other threads:[~2020-05-28 8:07 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-20 21:38 [bug#41425] [PATCH 0/5] Have 'guix pull' protect against downgrade attacks Ludovic Courtès
2020-05-20 21:47 ` [bug#41425] [PATCH 1/5] git: Add 'commit-relation' Ludovic Courtès
2020-05-20 21:47 ` [bug#41425] [PATCH 2/5] channels: 'latest-channel-instances' doesn't leak internal state Ludovic Courtès
2020-05-20 21:47 ` [bug#41425] [PATCH 3/5] git: 'update-cached-checkout' returns the commit relation Ludovic Courtès
2020-05-20 21:47 ` [bug#41425] [PATCH 4/5] channels: 'latest-channel-instances' guards against non-forward updates Ludovic Courtès
2020-05-20 21:47 ` [bug#41425] [PATCH 5/5] pull: Protect against downgrade attacks Ludovic Courtès
2020-05-21 14:06 ` [bug#41425] [PATCH 0/5] Have 'guix pull' protect " zimoun
2020-05-22 13:55 ` Ludovic Courtès
2020-05-25 14:36 ` zimoun
2020-05-27 16:32 ` Ludovic Courtès
2020-05-28 8:06 ` zimoun [this message]
2020-05-24 22:02 ` bug#41425: " Ludovic Courtès
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