//! Module to create a OCI runtime spec for a given [BuildRequest].
use crate::proto::BuildRequest;
use oci_spec::{
runtime::{Capability, LinuxNamespace, LinuxNamespaceBuilder, LinuxNamespaceType},
OciSpecError,
};
use std::{collections::HashSet, path::Path};
use tvix_castore::proto as castorepb;
use super::scratch_name;
/// For a given [BuildRequest], return an OCI runtime spec.
///
/// While there's no IO occuring in this function, the generated spec contains
/// path references relative to the "bundle location".
/// Due to overlayfs requiring its layers to be absolute paths, we also need a
/// [bundle_dir] parameter, pointing to the location of the bundle dir itself.
///
/// The paths used in the spec are the following (relative to a "bundle root"):
///
/// - `inputs`, a directory where the castore nodes specified the build request
/// inputs are supposed to be populated.
/// - `outputs`, a directory where all writes to the store_dir during the build
/// are directed to.
/// - `root`, a minimal skeleton of files that'll be present at /.
/// - `scratch`, a directory containing other directories which will be
/// bind-mounted read-write into the container and used as scratch space
/// during the build.
/// No assumptions should be made about what's inside this directory.
///
/// Generating these paths, and populating contents, like a skeleton root
/// is up to another function, this function doesn't do filesystem IO.
pub(crate) fn make_spec(
request: &BuildRequest,
rootless: bool,
sandbox_shell: &str,
) -> Result<oci_spec::runtime::Spec, oci_spec::OciSpecError> {
// TODO: add BuildRequest validations. BuildRequest must contain strings as inputs
let allow_network = request
.constraints
.as_ref()
.is_some_and(|c| c.network_access);
// Assemble ro_host_mounts. Start with constraints.available_ro_paths.
let mut ro_host_mounts = request
.constraints
.as_ref()
.map(|constraints| {
constraints
.available_ro_paths
.iter()
.map(|e| (e.as_str(), e.as_str()))
.collect::<Vec<_>>()
})
.unwrap_or_default();
// If provide_bin_sh is set, mount sandbox_shell to /bin/sh
if request
.constraints
.as_ref()
.is_some_and(|c| c.provide_bin_sh)
{
ro_host_mounts.push((sandbox_shell, "/bin/sh"))
}
oci_spec::runtime::SpecBuilder::default()
.process(configure_process(
&request.command_args,
&request.working_dir,
request
.environment_vars
.iter()
.map(|e| {
(
e.key.as_str(),
// TODO: decide what to do with non-bytes env values
String::from_utf8(e.value.to_vec()).expect("invalid string in env"),
)
})
.collect::<Vec<_>>(),
rootless,
)?)
.linux(configure_linux(allow_network, rootless)?)
.root(
oci_spec::runtime::RootBuilder::default()
.path("root")
.readonly(true)
.build()?,
)
.hostname("localhost")
.mounts(configure_mounts(
rootless,
allow_network,
request.scratch_paths.iter().map(|e| e.as_str()),
request.inputs.iter(),
&request.inputs_dir, // TODO: validate
ro_host_mounts,
)?)
.build()
}
/// Return the Process part of the OCI Runtime spec.
/// This configures the command, it's working dir, env and terminal setup.
/// It also takes care of setting rlimits and capabilities.
/// Capabilities are a bit more complicated in case rootless building is requested.
fn configure_process<'a>(
command_args: &[String],
cwd: &String,
env: impl IntoIterator<Item = (&'a str, String)>,
rootless: bool,
) -> Result<oci_spec::runtime::Process, oci_spec::OciSpecError> {
let spec_builder = oci_spec::runtime::ProcessBuilder::default()
.args(command_args)
.env(
env.into_iter()
.map(|(k, v)| format!("{}={}", k, v))
.collect::<Vec<_>>(),
)
.terminal(true)
.user(
oci_spec::runtime::UserBuilder::default()
.uid(1000u32)
.gid(100u32)
.build()?,
)
.cwd(Path::new("/").join(cwd)) // relative to the bundle root, but at least runc wants it to also be absolute.
.capabilities({
let caps: HashSet<Capability> = if !rootless {
HashSet::from([Capability::AuditWrite, Capability::Kill])
} else {
HashSet::from([
Capability::AuditWrite,
Capability::Chown,
Capability::DacOverride,
Capability::Fowner,
Capability::Fsetid,
Capability::Kill,
Capability::Mknod,
Capability::NetBindService,
Capability::NetRaw,
Capability::Setfcap,
Capability::Setgid,
Capability::Setpcap,
Capability::Setuid,
Capability::SysChroot,
])
};
oci_spec::runtime::LinuxCapabilitiesBuilder::default()
.bounding(caps.clone())
.effective(caps.clone())
.inheritable(caps.clone())
.permitted(caps.clone())
.ambient(caps)
.build()?
})
.rlimits([oci_spec::runtime::PosixRlimitBuilder::default()
.typ(oci_spec::runtime::PosixRlimitType::RlimitNofile)
.hard(1024_u64)
.soft(1024_u64)
.build()?])
.no_new_privileges(true);
spec_builder.build()
}
/// Return the Linux part of the OCI Runtime spec.
/// This configures various namespaces, masked and read-only paths.
fn configure_linux(
allow_network: bool,
rootless: bool,
) -> Result<oci_spec::runtime::Linux, OciSpecError> {
let mut linux = oci_spec::runtime::Linux::default();
// explicitly set namespaces, depending on allow_network.
linux.set_namespaces(Some({
let mut namespace_types = vec![
LinuxNamespaceType::Pid,
LinuxNamespaceType::Ipc,
LinuxNamespaceType::Uts,
LinuxNamespaceType::Mount,
LinuxNamespaceType::Cgroup,
];
if !allow_network {
namespace_types.push(LinuxNamespaceType::Network)
}
if rootless {
namespace_types.push(LinuxNamespaceType::User)
}
namespace_types
.into_iter()
.map(|e| LinuxNamespaceBuilder::default().typ(e).build())
.collect::<Result<Vec<LinuxNamespace>, _>>()?
}));
linux.set_masked_paths(Some(
[
"/proc/kcore",
"/proc/latency_stats",
"/proc/timer_list",
"/proc/timer_stats",
"/proc/sched_debug",
"/sys/firmware",
]
.into_iter()
.map(|e| e.to_string())
.collect::<Vec<_>>(),
));
linux.set_readonly_paths(Some(
[
"/proc/asound",
"/proc/bus",
"/proc/fs",
"/proc/irq",
"/proc/sys",
"/proc/sysrq-trigger",
]
.into_iter()
.map(|e| e.to_string())
.collect::<Vec<_>>(),
));
Ok(linux)
}
/// Return the Mounts part of the OCI Runtime spec.
/// It first sets up the standard mounts, then scratch paths, bind mounts for
/// all inputs, and finally read-only paths from the hosts.
fn configure_mounts<'a>(
rootless: bool,
allow_network: bool,
scratch_paths: impl IntoIterator<Item = &'a str>,
inputs: impl Iterator<Item = &'a castorepb::Node>,
inputs_dir: &str,
ro_host_mounts: impl IntoIterator<Item = (&'a str, &'a str)>,
) -> Result<Vec<oci_spec::runtime::Mount>, oci_spec::OciSpecError> {
let mut mounts: Vec<_> = if rootless {
oci_spec::runtime::get_rootless_mounts()
} else {
oci_spec::runtime::get_default_mounts()
};
mounts.push(configure_mount(
"tmpfs",
"/tmp",
"tmpfs",
&["nosuid", "noatime", "mode=700"],
)?);
// For each scratch path, create a bind mount entry.
let scratch_root = Path::new("scratch"); // relative path
for scratch_path in scratch_paths.into_iter() {
let src = scratch_root.join(scratch_name(scratch_path));
mounts.push(configure_mount(
src.to_str().unwrap(),
Path::new("/").join(scratch_path).to_str().unwrap(),
"none",
&["rbind", "rw"],
)?);
}
// For each input, create a bind mount from inputs/$name into $inputs_dir/$name.
for input in inputs {
let (input_name, _input) = input
.clone()
.into_name_and_node()
.expect("invalid input name");
let input_name = std::str::from_utf8(input_name.as_ref()).expect("invalid input name");
mounts.push(configure_mount(
Path::new("inputs").join(input_name).to_str().unwrap(),
Path::new("/")
.join(inputs_dir)
.join(input_name)
.to_str()
.unwrap(),
"none",
&[
"rbind", "ro",
// "nosuid" is required, otherwise mounting will just fail with
// a generic permission error.
// See https://github.com/wllenyj/containerd/commit/42a386c8164bef16d59590c61ab00806f854d8fd
"nosuid", "nodev",
],
)?);
}
// Process ro_host_mounts
for (src, dst) in ro_host_mounts.into_iter() {
mounts.push(configure_mount(src, dst, "none", &["rbind", "ro"])?);
}
// In case network is enabled, also mount in /etc/{resolv.conf,services,hosts}
if allow_network {
for p in ["/etc/resolv.conf", "/etc/services", "/etc/hosts"] {
mounts.push(configure_mount(p, p, "none", &["rbind", "ro"])?);
}
}
Ok(mounts)
}
/// Helper function to produce a mount.
fn configure_mount(
source: &str,
destination: &str,
typ: &str,
options: &[&str],
) -> Result<oci_spec::runtime::Mount, oci_spec::OciSpecError> {
oci_spec::runtime::MountBuilder::default()
.destination(destination.to_string())
.typ(typ.to_string())
.source(source.to_string())
.options(options.iter().map(|e| e.to_string()).collect::<Vec<_>>())
.build()
}
