If you have the Nix store mounted from a nonlocal filesystem whose
exporter is not running as root, making the directory mode 000 makes it
inaccessible to that remote unprivileged user and therefore breaks the
build. (Specifically, I am running into this with a virtiofs mount using
Apple Virtualization.framework as a non-root user, but I expect the
same thing would happen with virtiofs in qemu on Linux as a non-root
user or with various userspace network file servers.)
Make the directory mode 500 (dr-x------) to make the sandbox work in
this use case, which explicitly conveys our intention to read and search
the directory. The code only works because root can already bypass
directory checks, so this does not actually grant more permissions to
the directory owner / does not make the sandbox less secure.
This patch has been manually adapted from
14dc84ed03
Tested with:
$ NIX_SSL_CERT_FILE=$(nix-build '<nixpkgs>' -A cacert)/etc/ssl/certs/ca-bundle.crt nix-build --store $(mktemp -d) -E 'import <nix/fetchurl.nix> { url = https://google.com; }'
Finished at 16:57:50 after 1s
warning: found empty hash, assuming 'sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA='
this derivation will be built:
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
/nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
google.com> building '/nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv'
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
google.com> error:
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
google.com> … writing file '/nix/store/0zynn4n8yx59bczy1mgh1lq2rnprvvrc-google.com'
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
google.com>
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
google.com> error: unable to download 'https://google.com': Problem with the SSL CA cert (path? access rights?) (77) error setting certificate file: /nix/store/nlgbippbbgn38hynjkp1ghiybcq1dqhx-nss-cacert-3.101.1/etc/ssl/certs/ca-bundle.crt
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
error: builder for '/nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv' failed with exit code 1
Now returns:
nix-env % NIX_SSL_CERT_FILE=$(nix-build '<nixpkgs>' -A cacert)/etc/ssl/certs/ca-bundle.crt nix-build --store $(mktemp -d) -E 'import <nix/fetchurl.nix> { url = https://google.com; }'
Finished at 17:05:48 after 0s
warning: found empty hash, assuming 'sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA='
this derivation will be built:
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
/nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
google.com> building '/nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv'
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
nix-output-monitor error: DerivationReadError /nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv: openFile: does not exist (No such file or directory)
error: hash mismatch in fixed-output derivation '/nix/store/4qljhy0jj2b0abjzpsbyarpia1bqylwc-google.com.drv':
specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
Caused by 1d3696f0fb
Without this fix the kept build directory is readable only by root
```
$ sudo ls -ld /comp-temp/nix-build-openssh-static-x86_64-unknown-linux-musl-9.8p1.drv-5
drwx------ root root 60 B Wed Sep 11 00:09:48 2024 /comp-temp/nix-build-openssh-static-x86_64-unknown-linux-musl-9.8p1.drv-5/
$ sudo ls -ld /comp-temp/nix-build-openssh-static-x86_64-unknown-linux-musl-9.8p1.drv-5/build
drwxr-xr-x nixbld1 nixbld 80 B Wed Sep 11 00:09:58 2024 /comp-temp/nix-build-openssh-static-x86_64-unknown-linux-musl-9.8p1.drv-5/build/
```
The daemon process is now moved into a new sub-cgroup called nix-daemon when the
daemon starts. This is necessary to abide by the no-processes-in-inner-nodes
rule, because the service cgroup becomes an inner node when the child cgroups
for the build are created (see LocalDerivationGoal::startBuilder()).
See #9675
This reverts commit 43e82c9446, reversing
changes made to d79b9bdec0.
Since /proc/homeless-shelter returns a different errno than /homeless-shelter (ENOENT vs EACCES), we need to revert this change.
Software depends on this error code i.e. cargo and therefore breaks.
this is only used to close non-stdio files in derivation sandboxes. we
may as well encode that in its name, drop the unnecessary integer set,
and use close_range to deal with the actual closing of files. not only
is this clearer, it also makes sandbox setup on linux fast by 1ms each
(cherry-picked and adapted from
c7d97802e4)
Co-authored-by: Eelco Dolstra <edolstra@gmail.com>
Co-authored-by: Cole Helbling <cole.e.helbling@outlook.com>
Co-authored-by: John Ericson <git@JohnEricson.me>
This change updates the seccomp profile to return ENOTSUP for getxattr
functions family. This reflects the behavior of filesystems that don’t
support extended attributes (or have an option to disable them), e.g.
ext2.
The current behavior is confusing for some programs because we can read
extended attributes, but only get to know that they are not supported
when setting them. In addition to that, ACLs on Linux are implemented
via extended attributes internally and if we don’t return ENOTSUP, acl
library converts file mode to ACL.
https://git.savannah.nongnu.org/cgit/acl.git/tree/libacl/acl_get_file.c?id=d9bb1759d4dad2f28a6dcc8c1742ff75d16dd10d#n69
(System) features are unlikely to be empty strings, but when they
come in through structuredAttrs, they probably can.
I don't think this means we should drop them, but most likely they
will be dropped after this because next time they'll be parsed with
tokenizeString.
TODO: We should forbid empty features.
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 `$TMPDIR` at all.
The macOS sandbox probably shouldn’t be treated as any kind of a
security boundary in its current state, but this specific vulnerability
wasn’t possible to exploit on macOS anyway, as creating `set{u,g}id`
binaries is blocked by sandbox policy.
Locking down the build sandbox further may be a good idea in future,
but it already has significant compatibility issues. For now, restore
the previous status quo on macOS.
Thanks to @alois31 for helping me come to a better understanding of
the vulnerability.
Fixes: 1d3696f0fbCloses: #11002
Previously, the .chroot directory had permission 750 or 755 (depending
on the uid-range system feature) and was owned by root/nixbld. This
makes it possible for any nixbld user (if uid-range is disabled) or
any user (if uid-range is enabled) to inspect the contents of the
chroot of an active build and maybe interfere with it (e.g. via /tmp
in the chroot, which has 1777 permission).
To prevent this, the root is now a subdirectory of .chroot, which has
permission 700 and is owned by root/root.
Instead of running the builds under
`$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.
the old `copyFile` was just a wrapper that was calling the `copy`
function. This wrapper function is removed and the `copy` function is
renamed to `copyFile`.
Now that SourcePath uses a SourceAccessor instead of an InputAccessor,
we can use it in function signatures instead of passing a
SourceAccessor and CanonPath separately.
Make sure that `extraSandboxProfile` is set before we check whether it's
empty or not (in the `sandbox=true` case).
Also adds a test case for this.
Co-Authored-By: Artemis Tosini <lix@artem.ist>
Co-Authored-By: Eelco Dolstra <edolstra@gmail.com>
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
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>
2024-04-17 12:26:10 -04:00
Renamed from src/libstore/build/local-derivation-goal.cc (Browse further)
