Use `set -u` and `set -o pipefail` to catch accidental mistakes and
failures more strongly.
- `set -u` catches the use of undefined variables
- `set -o pipefail` catches failures (like `set -e`) earlier in the
pipeline.
This makes the tests a bit more robust. It is nice to read code not
worrying about these spurious success paths (via uncaught) errors
undermining the tests. Indeed, I caught some bugs doing this.
There are a few tests where we run a command that should fail, and then
search its output to make sure the failure message is one that we
expect. Before, since the `grep` was the last command in the pipeline
the exit code of those failing programs was silently ignored. Now with
`set -o pipefail` it won't be, and we have to do something so the
expected failure doesn't accidentally fail the test.
To do that we use `expect` and a new `expectStderr` to check for the
exact failing exit code. See the comments on each for why.
`grep -q` is replaced with `grepQuiet`, see the comments on that
function for why.
`grep -v` when we just want the exit code is replaced with `grepInverse,
see the comments on that function for why.
`grep -q -v` together is, surprise surprise, replaced with
`grepQuietInverse`, which is both combined.
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
Previously, getDefaultNixPath was called too early: at initialisation
time, before CLI and config have been processed, when `restrictEval` and
`pureEval` both have their default value `false`. Call it when
initialising the EvalState instead, and use `setDefault`.
This replaces the '(...)' installable syntax, which is not very
discoverable. The downside is that you can't have multiple expressions
or mix expressions and other installables.
In EvalState::checkSourcePath, the path is checked against the list of
allowed paths first and later it's checked again *after* resolving
symlinks.
The resolving of the symlinks is done via canonPath, which also strips
out "../" and "./". However after the canonicalisation the error message
pointing out that the path is not allowed prints the symlink target in
the error message.
Even if we'd suppress the message, symlink targets could still be leaked
if the symlink target doesn't exist (in this case the error is thrown in
canonPath).
So instead, we now do canonPath() without symlink resolving first before
even checking against the list of allowed paths and then later do the
symlink resolving and checking the allowed paths again.
The first call to canonPath() should get rid of all the "../" and "./",
so in theory the only way to leak a symlink if the attacker is able to
put a symlink in one of the paths allowed by restricted evaluation mode.
For the latter I don't think this is part of the threat model, because
if the attacker can write to that path, the attack vector is even
larger.
Signed-off-by: aszlig <aszlig@nix.build>
In this mode, the following restrictions apply:
* The builtins currentTime, currentSystem and storePath throw an
error.
* $NIX_PATH and -I are ignored.
* fetchGit and fetchMercurial require a revision hash.
* fetchurl and fetchTarball require a sha256 attribute.
* No file system access is allowed outside of the paths returned by
fetch{Git,Mercurial,url,Tarball}. Thus 'nix build -f ./foo.nix' is
not allowed.
Thus, the evaluation result is completely reproducible from the
command line arguments. E.g.
nix build --pure-eval '(
let
nix = fetchGit { url = https://github.com/NixOS/nixpkgs.git; rev = "9c927de4b179a6dd210dd88d34bda8af4b575680"; };
nixpkgs = fetchGit { url = https://github.com/NixOS/nixpkgs.git; ref = "release-17.09"; rev = "66b4de79e3841530e6d9c6baf98702aa1f7124e4"; };
in (import (nix + "/release.nix") { inherit nix nixpkgs; }).build.x86_64-linux
)'
The goal is to enable completely reproducible and traceable
evaluation. For example, a NixOS configuration could be fully
described by a single Git commit hash. 'nixos-rebuild' would do
something like
nix build --pure-eval '(
(import (fetchGit { url = file:///my-nixos-config; rev = "..."; })).system
')
where the Git repository /my-nixos-config would use further fetchGit
calls or Git externals to fetch Nixpkgs and whatever other
dependencies it has. Either way, the commit hash would uniquely
identify the NixOS configuration and allow it to reproduced.
