Install machine-wide screening on Windows with an MSI

The MSI installs both binaries, registers and starts the service with a
DACL that lets interactive users start, stop and pause it, restarts it on
failure, and sets NODE_EXTRA_CA_CERTS and UV_SYSTEM_CERTS. Removing it runs
`firewall-service.exe uninstall` once the service is deleted, which clears
the hosts entries and removes the CA, its TPM key and the data folder but
the config.

core/Cargo.toml

@@ -3,6 +3,7 @@ name = "strix-firewall"
 version = "0.1.0"
 edition = "2021"
 license = "Apache-2.0"
+authors = ["Strix"]
 description = "Screens package downloads for known malware before they reach your machine"
 repository = "https://github.com/usestrix/firewall"
 homepage = "https://github.com/usestrix/firewall"
@@ -18,6 +19,12 @@ x86_64-apple-darwin = ["firewall"]
 aarch64-unknown-linux-gnu = ["firewall"]
 x86_64-unknown-linux-gnu = ["firewall"]
 
+[package.metadata.wix]
+upgrade-guid = "D944C2F6-BF55-4B21-A60E-1BBDB1A66293"
+path-guid = "033B1050-23D0-4F5A-A0D3-F4757B4B67E0"
+license = false
+eula = false
+
 [lib]
 name = "firewall"
 # The macOS extension links a staticlib, built on demand:

core/src/bin/firewall-service.rs

@@ -2,14 +2,25 @@
 
 #[cfg(windows)]
 fn main() {
-    if let Err(e) = firewall::os::windows::run_service() {
-        tracing::error!("could not run the service: {e}");
-        firewall::telemetry::error("service");
-        firewall::telemetry::flush();
-        std::process::exit(1)
+    // Run by the MSI as it removes the firewall.
+    if std::env::args().nth(1).as_deref() == Some("uninstall") {
+        firewall::init_logging("info");
+        if let Err(e) = firewall::os::windows::uninstall() {
+            fail("uninstall", &format!("could not uninstall: {e}"))
+        }
+    } else if let Err(e) = firewall::os::windows::run_service() {
+        fail("service", &format!("could not run the service: {e}"))
     }
 }
 
+#[cfg(windows)]
+fn fail(kind: &'static str, message: &str) -> ! {
+    tracing::error!("{message}");
+    firewall::telemetry::error(kind);
+    firewall::telemetry::flush();
+    std::process::exit(1)
+}
+
 /// The service is Windows-only.
 #[cfg(not(windows))]
 fn main() {}

core/src/os/windows/ca.rs

@@ -7,9 +7,11 @@ use schannel::cert_context::CertContext;
 use schannel::cert_store::{CertAdd, CertStore};
 use std::io;
 use std::path::Path;
+use std::time::{SystemTime, UNIX_EPOCH};
 use tracing::warn;
 use windows::Win32::Security::Authorization::{GetNamedSecurityInfoW, SE_FILE_OBJECT};
 use windows::Win32::Security::*;
+use windows_registry::Type;
 
 /// SYSTEM and admins write, users only read, so no one else can plant a CA for node.
 const DATA_DIR_ACL: &str = concat!(
@@ -20,6 +22,9 @@ const DATA_DIR_ACL: &str = concat!(
     "(A;OICI;FRFX;;;BU)", // allow Users read and execute only
 );
 
+/// 1970 in FILETIME, which counts 100 ns from 1601.
+const FILETIME_UNIX_EPOCH: u128 = 116_444_736_000_000_000;
+
 /// Trusted machine-wide so restarts keep it; replaced if the hosts change.
 pub fn load_or_create_ca(
     hosts: &[&str],
@@ -34,6 +39,16 @@ pub fn load_or_create_ca(
             LOCAL_MACHINE
                 .create(REGISTRY_KEY)?
                 .set_string("ca", ca.to_blob(hosts))?;
+            // Windows discards CRLs it cached before now, in case an old CA's is cached at our URL.
+            let now = SystemTime::now().duration_since(UNIX_EPOCH)?.as_nanos() / 100
+                + FILETIME_UNIX_EPOCH;
+            let chain = r"SOFTWARE\Microsoft\Cryptography\OID\EncodingType 0\CertDllCreateCertificateChainEngine\Config";
+            let resync = (now as u64).to_le_bytes();
+            LOCAL_MACHINE.create(chain)?.set_bytes(
+                "ChainCacheResyncFiletime",
+                Type::Bytes,
+                &resync,
+            )?;
             ca
         }
     };

core/src/os/windows/mod.rs

@@ -4,9 +4,11 @@
 mod ca;
 mod service;
 mod tpm;
+mod uninstall;
 
 pub use service::run as run_service;
 pub use tpm::CaKey;
+pub use uninstall::uninstall;
 
 use rama::error::BoxError;
 use std::net::Ipv4Addr;

core/src/os/windows/tpm.rs

@@ -27,6 +27,13 @@ impl CaKey {
         }
     }
 
+    pub(super) fn delete_machine_key() -> Result<(), BoxError> {
+        if let Some(key) = open_key(KEY_NAME, NCRYPT_MACHINE_KEY_FLAG)? {
+            key.delete_from_tpm()?;
+        }
+        Ok(())
+    }
+
     /// A per-user key under a random name, which needs no elevation; `delete_from_tpm` it after.
     pub fn create_test_key() -> WinResult<Self> {
         let name = format!("Strix Firewall test {:016x}", rand::random::<u64>());

core/src/os/windows/uninstall.rs

@@ -0,0 +1,41 @@
+use super::ca::remove_our_cas_except;
+use super::tpm::CaKey;
+use super::*;
+use std::io::ErrorKind;
+use std::path::Path;
+use tracing::info;
+
+/// Run by the MSI after it deletes the service, which would restore the hosts entries. Does
+/// nothing for what is already gone.
+pub fn uninstall() -> Result<(), BoxError> {
+    write_hosts_entries(&[])?;
+    remove_our_cas_except(None)?;
+    none_if_missing(LOCAL_MACHINE.remove_tree(REGISTRY_KEY))?;
+    CaKey::delete_machine_key()?;
+    let entries = match std::fs::read_dir(data_dir()) {
+        Err(error) if error.kind() == ErrorKind::NotFound => Vec::new(),
+        entries => entries?.collect::<Result<Vec<_>, _>>()?,
+    };
+    for path in entries.into_iter().map(|entry| entry.path()) {
+        // The admin's config stays for a reinstall, as on macOS.
+        if path != config_file() {
+            remove_path(&path)?;
+        }
+    }
+    // Fails while the config is in it.
+    let _ = std::fs::remove_dir(data_dir());
+    info!("removed the CA, its key and the data folder");
+    Ok(())
+}
+
+/// A file or a folder, if it is there.
+fn remove_path(path: &Path) -> std::io::Result<()> {
+    let removed = match path.is_dir() {
+        true => std::fs::remove_dir_all(path),
+        false => std::fs::remove_file(path),
+    };
+    match removed {
+        Err(error) if error.kind() == ErrorKind::NotFound => Ok(()),
+        removed => removed,
+    }
+}

core/wix/main.wxs

@@ -0,0 +1,167 @@
+<?xml version='1.0' encoding='windows-1252'?>
+<!--
+  Copyright (C) 2017 Christopher R. Field.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+-->
+
+<?if $(sys.BUILDARCH) = x64 or $(sys.BUILDARCH) = arm64 ?>
+    <?define PlatformProgramFilesFolder = "ProgramFiles64Folder" ?>
+<?else ?>
+    <?define PlatformProgramFilesFolder = "ProgramFilesFolder" ?>
+<?endif ?>
+
+<Wix xmlns='http://schemas.microsoft.com/wix/2006/wi'>
+
+    <Product
+        Id='*'
+        Name='strix-firewall'
+        UpgradeCode='D944C2F6-BF55-4B21-A60E-1BBDB1A66293'
+        Manufacturer='Strix'
+        Language='1033'
+        Codepage='1252'
+        Version='$(var.Version)'>
+
+        <Package Id='*'
+            Keywords='Installer'
+            Description='Screens package downloads for known malware before they reach your machine'
+            Manufacturer='Strix'
+            InstallerVersion='500'
+            Languages='1033'
+            Compressed='yes'
+            InstallScope='perMachine'
+            SummaryCodepage='1252'
+            />
+
+        <MajorUpgrade
+            Schedule='afterInstallInitialize'
+            DowngradeErrorMessage='A newer version of [ProductName] is already installed. Setup will now exit.'/>
+
+        <Media Id='1' Cabinet='media1.cab' EmbedCab='yes' DiskPrompt='CD-ROM #1'/>
+        <Property Id='DiskPrompt' Value='strix-firewall Installation'/>
+
+        <Directory Id='TARGETDIR' Name='SourceDir'>
+            <Directory Id='$(var.PlatformProgramFilesFolder)' Name='PFiles'>
+                <Directory Id='APPLICATIONFOLDER' Name='Strix Firewall'>
+                    <Component Id='Path' Guid='033B1050-23D0-4F5A-A0D3-F4757B4B67E0' KeyPath='yes'>
+                        <Environment
+                            Id='PATH'
+                            Name='PATH'
+                            Value='[APPLICATIONFOLDER]'
+                            Permanent='no'
+                            Part='last'
+                            Action='set'
+                            System='yes'/>
+                    </Component>
+                    <Component Id='binary0' Guid='*'>
+                        <File
+                            Id='exe0'
+                            Name='firewall.exe'
+                            DiskId='1'
+                            Source='$(var.CargoTargetBinDir)\firewall.exe'
+                            KeyPath='yes'/>
+                    </Component>
+                    <Component Id='binary1' Guid='*'>
+                        <File
+                            Id='exe1'
+                            Name='firewall-service.exe'
+                            DiskId='1'
+                            Source='$(var.CargoTargetBinDir)\firewall-service.exe'
+                            KeyPath='yes'/>
+                        <ServiceInstall
+                            Name='StrixFirewall'
+                            DisplayName='Strix Firewall'
+                            Description='Screens package downloads for known malware'
+                            Type='ownProcess'
+                            Start='auto'
+                            ErrorControl='normal'
+                            Vital='yes'>
+                            <!-- The default, except that interactive users (IU) may also start (RP), stop (WP) and pause (DT) it, as the tray does. -->
+                            <PermissionEx Sddl='D:(A;;CCLCSWRPWPDTLOCRRC;;;SY)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;BA)(A;;CCLCSWRPWPDTLOCRRC;;;IU)(A;;CCLCSWLOCRRC;;;SU)'/>
+                        </ServiceInstall>
+                        <!-- Waits, so a service that cannot start fails the install. -->
+                        <ServiceControl Id='StrixFirewall' Name='StrixFirewall' Start='install' Stop='both' Remove='uninstall' Wait='yes'/>
+                        <!-- For clients that read no trust store. SSL_CERT_FILE would replace OpenSSL's bundle. -->
+                        <Environment Id='NODE_EXTRA_CA_CERTS' Name='NODE_EXTRA_CA_CERTS' Value='[CommonAppDataFolder]Strix Firewall\ca.pem' Action='set' System='yes'/>
+                        <Environment Id='UV_SYSTEM_CERTS' Name='UV_SYSTEM_CERTS' Value='1' Action='set' System='yes'/>
+                    </Component>
+                </Directory>
+            </Directory>
+        </Directory>
+
+        <Feature
+            Id='Binaries'
+            Title='Application'
+            Description='Installs the firewall and its service.'
+            Level='1'
+            ConfigurableDirectory='APPLICATIONFOLDER'
+            AllowAdvertise='no'
+            Display='expand'
+            Absent='disallow'>
+            <ComponentRef Id='binary0'/>
+            <ComponentRef Id='binary1'/>
+
+            <Feature
+                Id='Environment'
+                Title='PATH Environment Variable'
+                Description='Add the install location of the [ProductName] executable to the PATH system environment variable. This allows the [ProductName] executable to be called from any location.'
+                Level='1'
+                Absent='allow'>
+                <ComponentRef Id='Path'/>
+            </Feature>
+        </Feature>
+
+        <!-- Removing the app must not leave the hosts file pointing at a service that is gone. -->
+        <CustomAction
+            Id='UninstallFirewall'
+            FileKey='exe1'
+            ExeCommand='uninstall'
+            Execute='deferred'
+            Impersonate='no'
+            Return='check'/>
+        <!--
+          Registry hosts lead nowhere while the service is down, so bring it back, also when it fails to
+          start. Through sc.exe, as MsiServiceConfigFailureActions cannot restart a service.
+        -->
+        <CustomAction
+            Id='SetFailureActions'
+            Directory='APPLICATIONFOLDER'
+            ExeCommand='"[System64Folder]sc.exe" failure StrixFirewall reset= 3600 actions= restart/5000/restart/5000/restart/5000'
+            Execute='deferred'
+            Impersonate='no'
+            Return='check'/>
+        <CustomAction
+            Id='SetFailureFlag'
+            Directory='APPLICATIONFOLDER'
+            ExeCommand='"[System64Folder]sc.exe" failureflag StrixFirewall 1'
+            Execute='deferred'
+            Impersonate='no'
+            Return='check'/>
+        <InstallExecuteSequence>
+            <!-- An upgrade removes the old version too, but should keep screening. -->
+            <Custom Action='UninstallFirewall' After='DeleteServices'>REMOVE~="ALL" AND NOT UPGRADINGPRODUCTCODE</Custom>
+            <Custom Action='SetFailureActions' After='InstallServices'>NOT REMOVE~="ALL"</Custom>
+            <Custom Action='SetFailureFlag' After='SetFailureActions'>NOT REMOVE~="ALL"</Custom>
+        </InstallExecuteSequence>
+
+        <SetProperty Id='ARPINSTALLLOCATION' Value='[APPLICATIONFOLDER]' After='CostFinalize'/>
+        <Property Id='ARPHELPLINK' Value='https://github.com/usestrix/firewall'/>
+
+        <UI>
+            <UIRef Id='WixUI_FeatureTree'/>
+            <Publish Dialog='WelcomeDlg' Control='Next' Event='NewDialog' Value='CustomizeDlg' Order='99'>1</Publish>
+            <Publish Dialog='CustomizeDlg' Control='Back' Event='NewDialog' Value='WelcomeDlg' Order='99'>1</Publish>
+        </UI>
+    </Product>
+
+</Wix>

dist-workspace.toml

@@ -4,7 +4,9 @@ members = ["cargo:core"]
 [dist]
 cargo-dist-version = "0.32.0"
 ci = "github"
-installers = ["shell", "powershell", "homebrew"]
+installers = ["shell", "powershell", "homebrew", "msi"]
+# core/wix/main.wxs is edited to install the service.
+allow-dirty = ["msi"]
 tap = "usestrix/homebrew-tap"
 publish-jobs = ["homebrew", "./publish-crates"]
 targets = ["aarch64-apple-darwin", "x86_64-apple-darwin", "aarch64-unknown-linux-gnu", "x86_64-unknown-linux-gnu", "x86_64-pc-windows-msvc"]