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installer/cd-dvd/iso-image: avoid leaking build timestamps #75484

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raboof commented Dec 11, 2019

When 'grafting' '/nix/store/-loopback.cfg' from disk onto
'/boot/grub/loopback.cfg' on the iso, the parent 'grub' directory does not
exist yet. In this case it is automatically created and inherits its
attributes, including timestamp, from /nix/store.

This is correct/expected/intentional behavior of xorriso, but has the
undesired result of leaking the timestamps of /nix/store into the iso. For
this reason we put the loopback.cfg in a
'/nix/store/-loopback.cfg/grub/loopback.cfg' instead, so it will inherit
the attributes from the correctly-timestamped
'/nix/store/-loopback.cfg/grub' directory.

For the same reason we move '/EFI/boot/efi-background.png' down in the list
so it is grafted after its parent '/EFI/boot' directory is created with
the correct timestamp.

Motivation for this change

Making the installations ISO's bit-by-bit deterministic/reproducible for easier (security) checking, fixes #74944

Things done

Tested that together with #74174 nix-build ./nixos/release-combined.nix -A nixos.iso_minimal.x86_64-linux --check now succeeds

Notify maintainers

cc @bjornfor @veprbl

When 'grafting' '/nix/store/<hash>-loopback.cfg' from disk onto
'/boot/grub/loopback.cfg' on the iso, the parent 'grub' directory does not
exist yet. In this case it is automatically created and inherits its
attributes, including timestamp, from /nix/store.

This is correct/expected/intentional behavior of xorriso, but has the
undesired result of leaking the timestamps of /nix/store into the iso. For
this reason we put the loopback.cfg in a
'/nix/store/<hash>-loopback.cfg/grub/loopback.cfg' instead, so it will inherit
the attributes from the correctly-timestamped
'/nix/store/<hash>-loopback.cfg/grub' directory.

For the same reason we move '/EFI/boot/efi-background.png' down in the list
so it is grafted after its parent '/EFI/boot' directory is created with
the correct timestamp.

fixes #74944
@raboof raboof mentioned this pull request Dec 11, 2019
1 of 10 tasks complete
@domenkozar domenkozar merged commit 17d1925 into NixOS:master Dec 11, 2019
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Evaluation Performance Report Evaluator Performance Report
Details
grahamcofborg-eval ^.^!
Details
grahamcofborg-eval-check-meta config.nix: checkMeta = true
Details
grahamcofborg-eval-darwin nix-instantiate --arg nixpkgs { outPath=./.; revCount=999999; shortRev="ofborg"; } ./pkgs/top-level/release.nix -A darwin-tested
Details
grahamcofborg-eval-nixos nix-instantiate --arg nixpkgs { outPath=./.; revCount=999999; shortRev="ofborg"; } ./nixos/release-combined.nix -A tested
Details
grahamcofborg-eval-nixos-manual nix-instantiate --arg nixpkgs { outPath=./.; revCount=999999; shortRev="ofborg"; } ./nixos/release.nix -A manual
Details
grahamcofborg-eval-nixos-options nix-instantiate --arg nixpkgs { outPath=./.; revCount=999999; shortRev="ofborg"; } ./nixos/release.nix -A options
Details
grahamcofborg-eval-nixpkgs-manual nix-instantiate --arg nixpkgs { outPath=./.; revCount=999999; shortRev="ofborg"; } ./pkgs/top-level/release.nix -A manual
Details
grahamcofborg-eval-nixpkgs-tarball nix-instantiate --arg nixpkgs { outPath=./.; revCount=999999; shortRev="ofborg"; } ./pkgs/top-level/release.nix -A tarball
Details
grahamcofborg-eval-nixpkgs-unstable-jobset nix-instantiate --arg nixpkgs { outPath=./.; revCount=999999; shortRev="ofborg"; } ./pkgs/top-level/release.nix -A unstable
Details
grahamcofborg-eval-package-list nix-env -qa --json --file .
Details
grahamcofborg-eval-package-list-no-aliases nix-env -qa --json --file . --arg config { allowAliases = false; }
Details
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