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author | danbst <abcz2.uprola@gmail.com> | 2019-01-10 23:15:23 +0200 |
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committer | danbst <abcz2.uprola@gmail.com> | 2019-01-11 02:06:52 +0200 |
commit | 663b8cc9298c87940dde596e292006fad02393c1 (patch) | |
tree | c60fc9d6b97be851a0749f18b37492584d1c38a7 /doc | |
parent | 68a6b47b8cdbcef4cab3a1f5fae7667a792c27eb (diff) | |
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manual: document ways of obtaining source hashes
... and security nuances
Diffstat (limited to 'doc')
-rw-r--r-- | doc/Makefile | 6 | ||||
-rw-r--r-- | doc/coding-conventions.xml | 101 |
2 files changed, 105 insertions, 2 deletions
diff --git a/doc/Makefile b/doc/Makefile index c6aed62a939..91b62fe138b 100644 --- a/doc/Makefile +++ b/doc/Makefile @@ -9,8 +9,10 @@ debug: .PHONY: format format: - find . -iname '*.xml' -type f -print0 | xargs -0 -I{} -n1 \ - xmlformat --config-file "$$XMLFORMAT_CONFIG" -i {} + find . -iname '*.xml' -type f | while read f; do \ + echo $$f ;\ + xmlformat --config-file "$$XMLFORMAT_CONFIG" -i $$f ;\ + done .PHONY: fix-misc-xml fix-misc-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 { </itemizedlist> </para> </section> + <section xml:id="sec-source-hashes"> + <title>Obtaining source hash</title> + + <para> + Preferred source hash type is sha256. There are several ways to get it. + </para> + + <itemizedlist> + <listitem> + <para> + Prefetch URL (with <literal>nix-prefetch-<replaceable>XXX</replaceable> + <replaceable>URL</replaceable></literal>, where + <replaceable>XXX</replaceable> is one of <literal>url</literal>, + <literal>git</literal>, <literal>hg</literal>, <literal>cvs</literal>, + <literal>bzr</literal>, <literal>svn</literal>). Hash is printed to + stdout. + </para> + </listitem> + <listitem> + <para> + Prefetch by package source (with <literal>nix-prefetch-url + '<nixpkgs>' -A <replaceable>PACKAGE</replaceable>.src</literal>, + where <replaceable>PACKAGE</replaceable> is package attribute name). Hash + is printed to stdout. + </para> + <para> + 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 (<literal>.srcs</literal>, + architecture-dependent sources, etc). + </para> + </listitem> + <listitem> + <para> + Upstream provided hash: use it when upstream provides + <literal>sha256</literal> or <literal>sha512</literal> (when upstream + provides <literal>md5</literal>, don't use it, compute + <literal>sha256</literal> instead). + </para> + <para> + A little nuance is that <literal>nix-prefetch-*</literal> tools produce + hash encoded with <literal>base32</literal>, but upstream usually provides + hexadecimal (<literal>base16</literal>) encoding. Fetchers understand both + formats. Nixpkgs doesn't stadartize on any one format. + </para> + <para> + You can convert between formats with nix-hash, for example: +<screen> +$ nix-hash --type sha256 --to-base32 <replaceable>HASH</replaceable> +</screen> + </para> + </listitem> + <listitem> + <para> + Extracting hash from local source tarball can be done with + <literal>sha256sum</literal>. Use <literal>nix-prefetch-url + file:///path/to/tarball </literal> if you want base32 hash. + </para> + </listitem> + <listitem> + <para> + Fake hash: set fake hash in package expression, perform build and extract + correct hash from error Nix prints. + </para> + <para> + You can use <literal>lib.fakeSha256</literal>, + <literal>lib.fakeSha512</literal> or any other fake hash for this purpose. + This is last resort method when reconstructing source URL is non-trivial + and <literal>nix-prefetch-url -A</literal> isn't applicable (for example, + <link xlink:href="https://github.com/NixOS/nixpkgs/blob/d2ab091dd308b99e4912b805a5eb088dd536adb9/pkgs/applications/video/kodi/default.nix#L73"> + one of <literal>kodi</literal> dependencies</link>). 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. + </para> + </listitem> + </itemizedlist> + + <section xml:id="sec-source-hashes-security"> + <title>Obtaining hashes securely</title> + + <para> + From security point of view first four methods are most secure. + nix-prefetch-url does verify TLS certificates for + <literal>https://</literal> URLs. <emphasis>TLS certificates aren't + verified in fake hash method even when there is <literal>https://</literal> + URL</emphasis>. Obviously, getting hashes for <literal>http://</literal> + URLs isn't secure, so recheck using some other network that hash is same. + </para> + + <para> + Upstream provided hashes are not secure if obtained over + <literal>http://</literal>. + </para> + + <para> + 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. + </para> + </section> + </section> <section xml:id="sec-patches"> <title>Patches</title> |