bootstrap: verify signatures

src/cmd/init/bootstrap.rs

@@ -11,10 +11,10 @@ use crate::bootstrap::config::Config;
 use crate::{dkl, utils};
 
 pub async fn bootstrap(cfg: Config) {
+    let verifier = retry(async || Verifier::from_config(&cfg)).await;
     let bs = cfg.bootstrap;
 
     retry_or_ignore(async || {
-        fs::create_dir_all("/boostrap").await?;
         mount(Some(&bs.dev), "/bootstrap", "ext4", None).await;
         Ok(())
     })
@@ -33,12 +33,12 @@ pub async fn bootstrap(cfg: Config) {
     .await;
 
     let sys_cfg: dkl::Config = retry(async || {
-        let sys_cfg_bytes = seed_config(base_dir, &bs.seed).await?;
+        let sys_cfg_bytes = seed_config(base_dir, &bs.seed, &verifier).await?;
         Ok(serde_yaml::from_slice(&sys_cfg_bytes)?)
     })
     .await;
 
-    mount_system(&sys_cfg, base_dir).await;
+    mount_system(&sys_cfg, base_dir, &verifier).await;
 
     retry_or_ignore(async || {
         let path = "/etc/resolv.conf";
@@ -68,7 +68,67 @@ pub async fn bootstrap(cfg: Config) {
     exec("chroot", &["/system", "update-ca-certificates"]).await
 }
 
-async fn seed_config(base_dir: &str, seed_url: &Option<String>) -> Result<Vec<u8>> {
+struct Verifier {
+    pubkey: Option<Vec<u8>>,
+}
+impl Verifier {
+    fn from_config(cfg: &Config) -> Result<Self> {
+        let Some(ref pubkey) = cfg.signer_public_key else {
+            return Ok(Self { pubkey: None });
+        };
+
+        use base64::{prelude::BASE64_STANDARD, Engine};
+        let pubkey = BASE64_STANDARD.decode(pubkey)?;
+        let pubkey = Some(pubkey);
+
+        return Ok(Self { pubkey });
+    }
+
+    async fn verify_path(&self, path: &str) -> Result<()> {
+        let Some(ref pubkey) = self.pubkey else {
+            return Ok(());
+        };
+
+        info!("verifying {path}");
+
+        let mut pubkey = std::io::Cursor::new(pubkey);
+
+        let sig = format!("{path}.sig");
+
+        use std::process::Stdio;
+        use tokio::process::Command;
+
+        let mut openssl = Command::new("openssl")
+            .stdin(Stdio::piped())
+            .args(&[
+                "dgst",
+                "-sha512",
+                "-verify",
+                "/dev/stdin",
+                "-signature",
+                &sig,
+                path,
+            ])
+            .spawn()?;
+
+        tokio::io::copy(&mut pubkey, openssl.stdin.as_mut().unwrap()).await?;
+
+        let status = openssl.wait().await?;
+        if status.success() {
+            Ok(())
+        } else {
+            Err(format_err!(
+                "signature verification failed for {path}: {status}"
+            ))
+        }
+    }
+}
+
+async fn seed_config(
+    base_dir: &str,
+    seed_url: &Option<String>,
+    verifier: &Verifier,
+) -> Result<Vec<u8>> {
     let cfg_path = &format!("{base_dir}/config.yaml");
 
     if fs::try_exists(cfg_path).await? {
@@ -92,6 +152,8 @@ async fn seed_config(base_dir: &str, seed_url: &Option<String>) -> Result<Vec<u8
         return Err(format_err!("{cfg_path} does not exist after seeding"));
     }
 
+    verifier.verify_path(&cfg_path).await?;
+
     Ok(fs::read(cfg_path).await?)
 }
 
@@ -107,7 +169,7 @@ async fn fetch_bootstrap(seed_url: &str, output_file: &str) -> Result<()> {
     Ok(())
 }
 
-async fn mount_system(cfg: &dkl::Config, bs_dir: &str) {
+async fn mount_system(cfg: &dkl::Config, bs_dir: &str, verifier: &Verifier) {
     let mem_dir = "/mem";
     mount(None, mem_dir, "tmpfs", Some("size=512m")).await;
 
@@ -116,14 +178,17 @@ async fn mount_system(cfg: &dkl::Config, bs_dir: &str) {
 
     for layer in &cfg.layers {
         let src = if layer == "modules" {
-            "/modules.sqfs"
+            "/modules.sqfs".to_string()
         } else {
-            &format!("{bs_dir}/{layer}.fs")
+            let p = format!("{bs_dir}/{layer}.fs");
+            retry(async || verifier.verify_path(&p).await).await;
+            p
         };
+
         let tgt = &format!("{mem_dir}/{layer}.fs");
         retry(async || {
             info!("copying layer {layer} from {src}");
-            fs::copy(src, tgt).await?;
+            fs::copy(&src, tgt).await?;
             Ok(())
         })
         .await;