Add SELinux support (#465)

* Add SELinux support

* Nits

* Fix spellcheck

* Don't store mod, use locked shell

* Unwhoops a stale comment

* Speeling: Myy aarch neemesis

* Fix lost code:

* Add method note

.gitignore

@@ -2,3 +2,4 @@
 .ci-store
 .direnv
 result*
+src/action/linux/selinux/nix.mod

flake.lock

@@ -21,6 +21,22 @@
         "type": "github"
       }
     },
+    "flake-compat": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1673956053,
+        "narHash": "sha256-4gtG9iQuiKITOjNQQeQIpoIB6b16fm+504Ch3sNKLd8=",
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "rev": "35bb57c0c8d8b62bbfd284272c928ceb64ddbde9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
     "lowdown-src": {
       "flake": false,
       "locked": {
@@ -129,6 +145,7 @@
     "root": {
       "inputs": {
         "fenix": "fenix",
+        "flake-compat": "flake-compat",
         "naersk": "naersk",
         "nix": "nix",
         "nixpkgs": "nixpkgs_2"

flake.nix

@@ -19,6 +19,7 @@
       # Omitting `inputs.nixpkgs.follows = "nixpkgs";` on purpose
     };
 
+    flake-compat = { url = "github:edolstra/flake-compat"; flake = false; };
   };
 
   outputs =
@@ -139,6 +140,8 @@
               cacert
               cargo-audit
               nixpkgs-fmt
+              semodule-utils
+              checkpolicy
               check.check-rustfmt
               check.check-spelling
               check.check-nixpkgs-fmt

nix/check.nix

@@ -18,8 +18,8 @@ in
     runtimeInputs = with pkgs; [ git codespell ];
     text = ''
       codespell \
-        --ignore-words-list ba,sur,crate,pullrequest,pullrequests,ser,distroname \
-        --skip target,.git \
+        --ignore-words-list="ba,sur,crate,pullrequest,pullrequests,ser,distroname" \
+        --skip="./target,.git,./src/action/linux/selinux" \
         .
     '';
   });

nix/tests/vm-test/default.nix

@@ -174,7 +174,7 @@ let
       uninstallCheck = installCases.install-default.uninstallCheck;
     };
   };
-  cureCases = {
+  cureSelfCases = {
     cure-self-linux-working = {
       preinstall = ''
         ${nix-installer-install-quiet}
@@ -253,6 +253,8 @@ let
       uninstall = installCases.install-default.uninstall;
       uninstallCheck = installCases.install-default.uninstallCheck;
     };
+  };
+  cureScriptCases = {
     cure-script-multi-self-broken-no-nix-path = {
       preinstall = ''
         ${cure-script-multi-user}
@@ -413,7 +415,7 @@ let
       };
       rootDisk = "box.img";
       system = "x86_64-linux";
-      postBoot = disableSELinux;
+      upstreamScriptsWork = false; # SELinux!
     };
 
     "fedora-v37" = {
@@ -423,7 +425,7 @@ let
       };
       rootDisk = "box.img";
       system = "x86_64-linux";
-      postBoot = disableSELinux;
+      upstreamScriptsWork = false; # SELinux!
     };
 
     # Currently fails with 'error while loading shared libraries:
@@ -435,7 +437,7 @@ let
       hash = "sha256-QwzbvRoRRGqUCQptM7X/InRWFSP2sqwRt2HaaO6zBGM=";
       };
       rootDisk = "box.img";
-      postBoot = disableSELinux;
+      upstreamScriptsWork = false; # SELinux!
       system = "x86_64-linux";
       };
     */
@@ -446,7 +448,7 @@ let
         hash = "sha256-b4afnqKCO9oWXgYHb9DeQ2berSwOjS27rSd9TxXDc/U=";
       };
       rootDisk = "box.img";
-      postBoot = disableSELinux;
+      upstreamScriptsWork = false; # SELinux!
       system = "x86_64-linux";
     };
 
@@ -457,7 +459,7 @@ let
       };
       rootDisk = "box.img";
       system = "x86_64-linux";
-      postBoot = disableSELinux;
+      upstreamScriptsWork = false; # SELinux!
     };
 
     "rhel-v9" = {
@@ -467,7 +469,7 @@ let
       };
       rootDisk = "box.img";
       system = "x86_64-linux";
-      postBoot = disableSELinux;
+      upstreamScriptsWork = false; # SELinux!
       extraQemuOpts = "-cpu Westmere-v2";
     };
 
@@ -596,11 +598,13 @@ let
     )
     images;
 
-  allCases = lib.recursiveUpdate (lib.recursiveUpdate installCases cureCases) uninstallCases;
+  allCases = lib.recursiveUpdate (lib.recursiveUpdate installCases (lib.recursiveUpdate cureSelfCases cureScriptCases)) uninstallCases;
 
   install-tests = makeTests "install" installCases;
 
-  cure-tests = makeTests "cure" cureCases;
+  cure-self-tests = makeTests "cure-self" cureSelfCases;
+
+  cure-script-tests = makeTests "cure-script" cureScriptCases;
 
   uninstall-tests = makeTests "uninstall" uninstallCases;
 
@@ -610,14 +614,14 @@ let
         name = "all";
         constituents = [
           install-tests."${imageName}"."x86_64-linux".install
-          cure-tests."${imageName}"."x86_64-linux".cure
+          cure-self-tests."${imageName}"."x86_64-linux".cure-self
           uninstall-tests."${imageName}"."x86_64-linux".uninstall
-        ];
+        ] ++ (lib.optional (image.upstreamScriptsWork or false) cure-script-tests."${imageName}"."x86_64-linux".cure-script);
       });
     })
     images;
 
-  joined-tests = lib.recursiveUpdate (lib.recursiveUpdate (lib.recursiveUpdate cure-tests install-tests) uninstall-tests) all-tests;
+  joined-tests = lib.recursiveUpdate (lib.recursiveUpdate (lib.recursiveUpdate install-tests (lib.recursiveUpdate cure-self-tests cure-script-tests)) uninstall-tests) all-tests;
 
 in
 lib.recursiveUpdate joined-tests {
@@ -626,5 +630,5 @@ lib.recursiveUpdate joined-tests {
       name = caseName;
       constituents = pkgs.lib.mapAttrsToList (name: value: value."x86_64-linux"."${caseName}") joined-tests;
     }
-  )) (allCases // { "cure" = { }; "install" = { }; "uninstall" = { }; "all" = { }; });
+  )) (allCases // { "cure-self" = { }; "cure-script" = { }; "install" = { }; "uninstall" = { }; "all" = { }; });
 }

src/action/common/configure_init_service.rs

@@ -300,6 +300,12 @@ impl Action for ConfigureInitService {
                 Self::check_if_systemd_unit_exists(SERVICE_SRC, SERVICE_DEST)
                     .await
                     .map_err(Self::error)?;
+                if Path::new(SERVICE_DEST).exists() {
+                    tokio::fs::remove_file(SERVICE_DEST)
+                        .await
+                        .map_err(|e| ActionErrorKind::Remove(SERVICE_DEST.into(), e))
+                        .map_err(Self::error)?;
+                }
                 tokio::fs::symlink(SERVICE_SRC, SERVICE_DEST)
                     .await
                     .map_err(|e| {
@@ -310,10 +316,15 @@ impl Action for ConfigureInitService {
                         )
                     })
                     .map_err(Self::error)?;
-
                 Self::check_if_systemd_unit_exists(SOCKET_SRC, SOCKET_DEST)
                     .await
                     .map_err(Self::error)?;
+                if Path::new(SOCKET_DEST).exists() {
+                    tokio::fs::remove_file(SOCKET_DEST)
+                        .await
+                        .map_err(|e| ActionErrorKind::Remove(SOCKET_DEST.into(), e))
+                        .map_err(Self::error)?;
+                }
                 tokio::fs::symlink(SOCKET_SRC, SOCKET_DEST)
                     .await
                     .map_err(|e| {

src/action/linux/mod.rs

@@ -1,3 +1,5 @@
+pub(crate) mod provision_selinux;
 pub(crate) mod start_systemd_unit;
 
+pub use provision_selinux::ProvisionSelinux;
 pub use start_systemd_unit::{StartSystemdUnit, StartSystemdUnitError};

src/action/linux/provision_selinux.rs

@@ -0,0 +1,125 @@
+use std::path::{Path, PathBuf};
+
+use tokio::fs::{create_dir_all, remove_file};
+use tokio::process::Command;
+use tracing::{span, Span};
+
+use crate::action::{ActionError, ActionErrorKind, ActionTag};
+use crate::execute_command;
+
+use crate::action::{Action, ActionDescription, StatefulAction};
+
+const SE_LINUX_POLICY_PP_CONTENT: &[u8] = include_bytes!("selinux/nix.pp");
+
+/**
+Provision the selinux/nix.pp for SELinux compatibility
+*/
+#[derive(Debug, serde::Deserialize, serde::Serialize, Clone)]
+pub struct ProvisionSelinux {
+    policy_path: PathBuf,
+}
+
+impl ProvisionSelinux {
+    #[tracing::instrument(level = "debug", skip_all)]
+    pub async fn plan(policy_path: PathBuf) -> Result<StatefulAction<Self>, ActionError> {
+        let this = Self { policy_path };
+
+        // Note: `restorecon` requires us to not just skip this, even if everything is in place.
+
+        Ok(StatefulAction::uncompleted(this))
+    }
+}
+
+#[async_trait::async_trait]
+#[typetag::serde(name = "provision_selinux")]
+impl Action for ProvisionSelinux {
+    fn action_tag() -> ActionTag {
+        ActionTag("provision_selinux")
+    }
+    fn tracing_synopsis(&self) -> String {
+        format!("Install an SELinux Policy for Nix")
+    }
+
+    fn tracing_span(&self) -> Span {
+        span!(
+            tracing::Level::DEBUG,
+            "provision_selinux",
+            policy_path = %self.policy_path.display()
+        )
+    }
+
+    fn execute_description(&self) -> Vec<ActionDescription> {
+        vec![ActionDescription::new(
+            self.tracing_synopsis(),
+            vec![format!(
+                "On SELinux systems (such as Fedora) a policy for Nix needs to be configured for correct operation."
+            )],
+        )]
+    }
+
+    #[tracing::instrument(level = "debug", skip_all)]
+    async fn execute(&mut self) -> Result<(), ActionError> {
+        if self.policy_path.exists() {
+            // Rebuild it.
+            remove_existing_policy(&self.policy_path)
+                .await
+                .map_err(Self::error)?;
+        }
+
+        if let Some(parent) = self.policy_path.parent() {
+            create_dir_all(&parent)
+                .await
+                .map_err(|e| ActionErrorKind::CreateDirectory(parent.into(), e))
+                .map_err(Self::error)?;
+        }
+
+        tokio::fs::write(&self.policy_path, SE_LINUX_POLICY_PP_CONTENT)
+            .await
+            .map_err(|e| ActionErrorKind::Write(self.policy_path.clone(), e))
+            .map_err(Self::error)?;
+
+        execute_command(
+            Command::new("semodule")
+                .arg("--install")
+                .arg(&self.policy_path),
+        )
+        .await
+        .map_err(Self::error)?;
+
+        execute_command(Command::new("restorecon").args(["-FR", "/nix"]))
+            .await
+            .map_err(Self::error)?;
+
+        Ok(())
+    }
+
+    fn revert_description(&self) -> Vec<ActionDescription> {
+        vec![ActionDescription::new(
+            "Remove the SELinux policy for Nix".into(),
+            vec![],
+        )]
+    }
+
+    #[tracing::instrument(level = "debug", skip_all)]
+    async fn revert(&mut self) -> Result<(), ActionError> {
+        if self.policy_path.exists() {
+            remove_existing_policy(&self.policy_path)
+                .await
+                .map_err(Self::error)?;
+        }
+
+        Ok(())
+    }
+}
+
+async fn remove_existing_policy(policy_path: &Path) -> Result<(), ActionErrorKind> {
+    execute_command(Command::new("semodule").arg("--remove").arg("nix")).await?;
+
+    remove_file(&policy_path)
+        .await
+        .map_err(|e| ActionErrorKind::Remove(policy_path.into(), e))?;
+
+    execute_command(Command::new("restorecon").args(["-FR", "/nix"])).await?;
+
+    Ok(())
+}

src/action/linux/selinux/README.md

@@ -0,0 +1,9 @@
+To refresh the output `pp` file:
+
+```bash
+./build.sh
+```
+
+## Method
+
+We use the same method and definitions as https://github.com/nix-community/nix-installers/tree/master/selinux.

src/action/linux/selinux/build.sh

@@ -0,0 +1,5 @@
+#! /usr/bin/env nix-shell
+#! nix-shell -i bash ../../../../shell.nix
+
+checkmodule -M -m -c 5 -o nix.mod nix.te
+semodule_package -o nix.pp -m nix.mod -f nix.fc

src/action/linux/selinux/nix.fc

@@ -0,0 +1,8 @@
+/nix/store/[^/]+/s?bin(/.*)?	system_u:object_r:bin_t:s0
+/nix/store/[^/]+/lib/systemd/system(/.*)?	system_u:object_r:systemd_unit_file_t:s0
+/nix/store/[^/]+/lib(/.*)?	system_u:object_r:lib_t:s0
+/nix/store/[^/]+/man(/.*)?	system_u:object_r:man_t:s0
+/nix/store/[^/]+/etc(/.*)?	system_u:object_r:etc_t:s0
+/nix/store/[^/]+/share(/.*)?	system_u:object_r:usr_t:s0
+/nix/var/nix/daemon-socket(/.*)?	system_u:object_r:var_run_t:s0
+/nix/var/nix/profiles(/per-user/[^/]+)?/[^/]+	system_u:object_r:usr_t:s0

src/action/linux/selinux/nix.te

@@ -0,0 +1,11 @@
+module nix 1.0;
+
+require {
+  type bin_t;
+  type lib_t;
+  type man_t;
+  type usr_t;
+  type etc_t;
+  type var_run_t;
+  type systemd_unit_file_t;
+}

src/planner/linux.rs

@@ -2,6 +2,7 @@ use crate::{
     action::{
         base::{CreateDirectory, RemoveDirectory},
         common::{ConfigureInitService, ConfigureNix, ProvisionNix},
+        linux::ProvisionSelinux,
         StatefulAction,
     },
     error::HasExpectedErrors,
@@ -12,6 +13,7 @@ use crate::{
 };
 use std::{collections::HashMap, path::Path};
 use tokio::process::Command;
+use which::which;
 
 use super::ShellProfileLocations;
 
@@ -42,25 +44,44 @@ impl Planner for Linux {
 
         check_not_wsl1()?;
 
-        check_not_selinux().await?;
+        let has_selinux = detect_selinux().await?;
 
         if self.init.init == InitSystem::Systemd && self.init.start_daemon {
             check_systemd_active()?;
         }
 
-        Ok(vec![
+        let mut plan = vec![];
+
+        plan.push(
             CreateDirectory::plan("/nix", None, None, 0o0755, true)
                 .await
                 .map_err(PlannerError::Action)?
                 .boxed(),
+        );
+
+        plan.push(
             ProvisionNix::plan(&self.settings.clone())
                 .await
                 .map_err(PlannerError::Action)?
                 .boxed(),
+        );
+        plan.push(
             ConfigureNix::plan(ShellProfileLocations::default(), &self.settings)
                 .await
                 .map_err(PlannerError::Action)?
                 .boxed(),
+        );
+
+        if has_selinux {
+            plan.push(
+                ProvisionSelinux::plan("/usr/share/selinux/packages/nix.pp".into())
+                    .await
+                    .map_err(PlannerError::Action)?
+                    .boxed(),
+            );
+        }
+
+        plan.push(
             ConfigureInitService::plan(
                 self.init.init,
                 self.init.start_daemon,
@@ -69,11 +90,15 @@ impl Planner for Linux {
             .await
             .map_err(PlannerError::Action)?
             .boxed(),
+        );
+        plan.push(
             RemoveDirectory::plan(crate::settings::SCRATCH_DIR)
                 .await
                 .map_err(PlannerError::Action)?
                 .boxed(),
-        ])
+        );
+
+        Ok(plan)
     }
 
     fn settings(&self) -> Result<HashMap<String, serde_json::Value>, InstallSettingsError> {
@@ -139,26 +164,19 @@ fn check_not_wsl1() -> Result<(), PlannerError> {
     Ok(())
 }
 
-async fn check_not_selinux() -> Result<(), PlannerError> {
-    // We currently do not support SELinux
-    match Command::new("getenforce").output().await {
-        Ok(output) => {
-            let stdout_string = String::from_utf8(output.stdout).map_err(PlannerError::Utf8)?;
-            tracing::trace!(getenforce_stdout = stdout_string, "SELinux detected");
-            match stdout_string.trim() {
-                "Enforcing" => return Err(PlannerError::SelinuxEnforcing),
-                _ => (),
+async fn detect_selinux() -> Result<bool, PlannerError> {
+    if Path::new("/sys/fs/selinux").exists() {
+        // We expect systems with SELinux to have the normal SELinux tools.
+        let has_semodule = which("semodule").is_ok();
+        let has_restorecon = which("restorecon").is_ok();
+        if !(has_semodule && has_restorecon) {
+            Err(PlannerError::SelinuxRequirements)
+        } else {
+            Ok(true)
         }
-        },
-        // The device doesn't have SELinux set up
-        Err(e) if e.kind() == std::io::ErrorKind::NotFound => (),
-        // Some unknown error
-        Err(e) => {
-            tracing::warn!(error = ?e, "Got an error checking for SELinux setting, this install may fail if SELinux is set to `Enforcing`")
-        },
+    } else {
+        Ok(false)
     }
-
-    Ok(())
 }
 
 async fn check_nix_not_already_installed() -> Result<(), PlannerError> {

src/planner/mod.rs

@@ -367,13 +367,8 @@ pub enum PlannerError {
     #[error("Detected that this process is running under Rosetta, using Nix in Rosetta is not supported (Please open an issue with your use case)")]
     RosettaDetected,
     /// A Linux SELinux related error
-    #[error("\
-        This installer doesn't yet support SELinux in `Enforcing` mode.\n
-        \n\
-        If desirable, consider setting SELinux to `Permissive` mode with `setenforce Permissive`.\n\
-        \n\
-        If SELinux is important to you, please see https://github.com/DeterminateSystems/nix-installer/issues/124.")]
-    SelinuxEnforcing,
+    #[error("Unable to install on an SELinux system without common SELinux tooling, the binaries `restorecon`, and `semodule` are required")]
+    SelinuxRequirements,
     /// A UTF-8 related error
     #[error("UTF-8 error")]
     Utf8(#[from] FromUtf8Error),
@@ -401,7 +396,7 @@ impl HasExpectedErrors for PlannerError {
             PlannerError::Sysctl(_) => None,
             this @ PlannerError::RosettaDetected => Some(Box::new(this)),
             PlannerError::Utf8(_) => None,
-            PlannerError::SelinuxEnforcing => Some(Box::new(self)),
+            PlannerError::SelinuxRequirements => Some(Box::new(self)),
             PlannerError::Custom(e) => {
                 #[cfg(target_os = "linux")]
                 if let Some(err) = e.downcast_ref::<linux::LinuxErrorKind>() {