From 663b8cc9298c87940dde596e292006fad02393c1 Mon Sep 17 00:00:00 2001 From: danbst Date: Thu, 10 Jan 2019 23:15:23 +0200 Subject: manual: document ways of obtaining source hashes ... and security nuances --- doc/coding-conventions.xml | 101 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 101 insertions(+) (limited to 'doc/coding-conventions.xml') diff --git a/doc/coding-conventions.xml b/doc/coding-conventions.xml index a8a4557b461..88ce6281a25 100644 --- a/doc/coding-conventions.xml +++ b/doc/coding-conventions.xml @@ -876,6 +876,107 @@ src = fetchFromGitHub { +
+ Obtaining source hash + + + Preferred source hash type is sha256. There are several ways to get it. + + + + + + Prefetch URL (with nix-prefetch-XXX + URL, where + XXX is one of url, + git, hg, cvs, + bzr, svn). Hash is printed to + stdout. + + + + + Prefetch by package source (with nix-prefetch-url + '<nixpkgs>' -A PACKAGE.src, + where PACKAGE is package attribute name). Hash + is printed to stdout. + + + This works well when you've upgraded existing package version and want to + find out new hash, but is useless if package doesn't have top-level + attribute or package has multiple sources (.srcs, + architecture-dependent sources, etc). + + + + + Upstream provided hash: use it when upstream provides + sha256 or sha512 (when upstream + provides md5, don't use it, compute + sha256 instead). + + + A little nuance is that nix-prefetch-* tools produce + hash encoded with base32, but upstream usually provides + hexadecimal (base16) encoding. Fetchers understand both + formats. Nixpkgs doesn't stadartize on any one format. + + + You can convert between formats with nix-hash, for example: + +$ nix-hash --type sha256 --to-base32 HASH + + + + + + Extracting hash from local source tarball can be done with + sha256sum. Use nix-prefetch-url + file:///path/to/tarball if you want base32 hash. + + + + + Fake hash: set fake hash in package expression, perform build and extract + correct hash from error Nix prints. + + + You can use lib.fakeSha256, + lib.fakeSha512 or any other fake hash for this purpose. + This is last resort method when reconstructing source URL is non-trivial + and nix-prefetch-url -A isn't applicable (for example, + + one of kodi dependencies). The easiest way then + would be replace hash with a fake one and rebuild. Nix build will fail and + error message will contain wanted hash. + + + + +
+ Obtaining hashes securely + + + From security point of view first four methods are most secure. + nix-prefetch-url does verify TLS certificates for + https:// URLs. TLS certificates aren't + verified in fake hash method even when there is https:// + URL. Obviously, getting hashes for http:// + URLs isn't secure, so recheck using some other network that hash is same. + + + + Upstream provided hashes are not secure if obtained over + http://. + + + + Nixpkgs build farm can act as an additional verification step. When + compromised hash was obtained, package may be rejected on Hydra due to hash + mismatch. + +
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Patches -- cgit 1.4.1