In d60c3f7f7c, this was changed to close a
hole in the sandbox. Unfortunately, this was too restrictive such that it
made local port binding fail, thus making derivations that needed
`__darwinAllowLocalNetworking` gain nearly nothing, and thus largely
fail (as the primary use for it is to enable port binding).
This unfortunately does mean that a sandboxed build process can, in
coordination with an actor outside the sandbox, escape the sandbox by
binding a port and connecting to it externally to send data. I do not
see a way around this with my experimentation and understanding of the
(quite undocumented) macOS sandbox profile API. Notably it seems not
possible to use the sandbox to do any of:
- Restrict the remote IP of inbound network requests
- Restrict the address being bound to
As such, the `(local ip "*:*")` here appears to be functionally no
different than `(local ip "localhost:*")` (however it *should* be
different than removing the filter entirely, as that would make it also
apply to non-IP networking). Doing `(allow network-inbound (require-all
(local ip "localhost:*") (remote ip "localhost:*")))` causes listening
to fail.
Note that `network-inbound` implies `network-bind`.
(cherry picked from commit 00f6db36fd)
This happens in parallel with the download (which starts later), so
you only see this message when the download has finished but the
import hasn't.
(cherry picked from commit 01839b525c)
We are piping curl downloads into `unpackTarfileToSink()`, but the
latter is typically slower than the former if you're on a fast
connection. So the download could appear unnecessarily slow. (There is
even a risk that if the Git import is *really* slow for whatever
reason, the TCP connection could time out.)
So let's make the download buffer bigger by default - 64 MiB is big
enough for the Nixpkgs tarball. Perhaps in the future, we could have
an unlimited buffer that spills data to disk beyond a certain
threshold, but that's probably overkill.
(cherry picked from commit 8ffea0a018)
The recent fix for CVE-2024-38531 broke the sandbox on macOS
completely. As it’s not practical to use `chroot(2)` on
macOS, the build takes place in the main filesystem tree, and the
world‐unreadable wrapper directory prevents the build from accessing
its `$TMPDIR` at all.
The macOS sandbox probably shouldn’t be treated as any kind of a
security boundary in its current state, but this specific vulnerability
wasn’t possible to exploit on macOS anyway, as creating `set{u,g}id`
binaries is blocked by sandbox policy.
Locking down the build sandbox further may be a good idea in future,
but it already has significant compatibility issues. For now, restore
the previous status quo on macOS.
Thanks to @alois31 for helping me come to a better understanding of
the vulnerability.
Fixes: 1d3696f0fbCloses: #11002
(cherry picked from commit af2e1142b1)
After the fix for CVE-2024-38531, this was only removing the nested
build directory, rather than the top‐level temporary directory.
Fixes: 1d3696f0fb
(cherry picked from commit 76e4adfaac)
Previously, the .chroot directory had permission 750 or 755 (depending
on the uid-range system feature) and was owned by root/nixbld. This
makes it possible for any nixbld user (if uid-range is disabled) or
any user (if uid-range is enabled) to inspect the contents of the
chroot of an active build and maybe interfere with it (e.g. via /tmp
in the chroot, which has 1777 permission).
To prevent this, the root is now a subdirectory of .chroot, which has
permission 700 and is owned by root/root.
(cherry picked from commit ede95b1fc1)
Instead of running the builds under
`$TMPDIR/{unique-build-directory-owned-by-the-build-user}`, run them
under `$TMPDIR/{unique-build-directory-owned-by-the-daemon}/{subdir-owned-by-the-build-user}`
where the build directory is only readable and traversable by the daemon user.
This achieves two things:
1. It prevents builders from making their build directory world-readable
(or even writeable), which would allow the outside world to interact
with them.
2. It prevents external processes running as the build user (either
because that somehow leaked, maybe as a consequence of 1., or because
`build-users` isn't in use) from gaining access to the build
directory.
(cherry picked from commit 1d3696f0fb)
Previously, the "file:./" prefix was not correctly recognized in
fixGitURL; instead, it was mistaken as a file path, which resulted in a
parsed url of the form "file://file:./".
This commit fixes the issue by properly detecting the "file:" prefix.
Note, however, that unlike "file://", the "file:./" URI is _not_
standardized, but has been widely used to referred to relative file
paths. In particular, the "git+file:./" did work for nix<=2.18, and was
broken since nix 2.19.0.
Finally, this commit fixes the issue completely for the 2.19 series, but
is still inadequate for the 2.20 series due to new behaviors from the
switch to libgit2. However, it does improve the correctness of parsing
even though it is not yet a complete solution.
(cherry picked from commit 8594f3cd5a)
In streaming mode, libarchive doesn't handle symlinks in zip files
correctly. So write the entire file to disk so libarchive can access
it in random-access mode.
Fixes#10649. This was broken in cabee98152.
(cherry picked from commit 9951e14ae0)
Passing the commit message as an argument causes update failures on repositories with lots of flake inputs. In some cases, the commit message is over 250,000 bytes.
(cherry picked from commit 8b5e8f4fba)
With Linux kernel >=6.6 & glibc 2.39 a `fchmodat2(2)` is available that
isn't filtered away by the libseccomp sandbox.
Being able to use this to bypass that restriction has surprising results
for some builds such as lxc[1]:
> With kernel ≥6.6 and glibc 2.39, lxc's install phase uses fchmodat2,
> which slips through 9b88e52846/src/libstore/build/local-derivation-goal.cc (L1650-L1663).
> The fixupPhase then uses fchmodat, which fails.
> With older kernel or glibc, setting the suid bit fails in the
> install phase, which is not treated as fatal, and then the
> fixup phase does not try to set it again.
Please note that there are still ways to bypass this sandbox[2] and this is
mostly a fix for the breaking builds.
This change works by creating a syscall filter for the `fchmodat2`
syscall (number 452 on most systems). The problem is that glibc 2.39
and seccomp 2.5.5 are needed to have the correct syscall number available
via `__NR_fchmodat2` / `__SNR_fchmodat2`, but this flake is still on
nixpkgs 23.11. To have this change everywhere and not dependent on the
glibc this package is built against, I added a header
"fchmodat2-compat.hh" that sets the syscall number based on the
architecture. On most platforms its 452 according to glibc with a few
exceptions:
$ rg --pcre2 'define __NR_fchmodat2 (?!452)'
sysdeps/unix/sysv/linux/x86_64/x32/arch-syscall.h
58:#define __NR_fchmodat2 1073742276
sysdeps/unix/sysv/linux/mips/mips64/n32/arch-syscall.h
67:#define __NR_fchmodat2 6452
sysdeps/unix/sysv/linux/mips/mips64/n64/arch-syscall.h
62:#define __NR_fchmodat2 5452
sysdeps/unix/sysv/linux/mips/mips32/arch-syscall.h
70:#define __NR_fchmodat2 4452
sysdeps/unix/sysv/linux/alpha/arch-syscall.h
59:#define __NR_fchmodat2 562
I tested the change by adding the diff below as patch to
`pkgs/tools/package-management/nix/common.nix` & then built a VM from
the following config using my dirty nixpkgs master:
{
vm = { pkgs, ... }: {
virtualisation.writableStore = true;
virtualisation.memorySize = 8192;
virtualisation.diskSize = 12 * 1024;
nix.package = pkgs.nixVersions.nix_2_21;
};
}
The original issue can be triggered via
nix build -L github:nixos/nixpkgs/d6dc19adbda4fd92fe9a332327a8113eaa843894#lxc \
--extra-experimental-features 'nix-command flakes'
however the problem disappears with this patch applied.
Closes#10424
[1] https://github.com/NixOS/nixpkgs/issues/300635#issuecomment-2031073804
[2] https://github.com/NixOS/nixpkgs/issues/300635#issuecomment-2030844251
With Nix 2.3, it was possible to pass a subpath of a store path to
exportReferencesGraph:
with import <nixpkgs> {};
let
hello = writeShellScriptBin "hello" ''
echo ${toString builtins.currentTime}
'';
in
writeClosure [ "${hello}/bin/hello" ]
This regressed with Nix 2.4, with a very confusing error message, that
presumably indicates it was unintentional:
error: path '/nix/store/3gl7kgjr4pwf03f0x70dgx9ln3bhl7zc-hello/bin/hello' is not in the Nix store
At this point many features are stripped out, but this works:
- Can run libnix{util,store,expr} unit tests
- Can run some Nix commands
Co-Authored-By volth <volth@volth.com>
Co-Authored-By Brian McKenna <brian@brianmckenna.org>
