fix: validate image name before building registry path

The user-supplied image/name argument was interpolated unsanitized into registry/{name}/initrd, so a name containing '../' (e.g. 'slim run ../../.ssh/authorized_keys') escaped the XDG data dir and let slim create directories and read/write files at attacker-chosen locations. validate_image_name now rejects empty names, '.', '..' and anything outside [A-Za-z0-9._:-] at the registry_dir chokepoint used by both build and run, plus a defense-in-depth containment check that the resolved path stays under the registry root. Fixes sec-2 from the code review.
Fix minor issues
2026-08-26 20:11:57 +00:00 · 2026-08-26 21:45:26 +02:00 · 2026-08-26 19:25:20 +02:00
3 changed files with 488 additions and 39 deletions
@@ -1,4 +1 @@
-/target/
-/target/debug/
-/target/release/
-Cargo.lock
+target
@@ -0,0 +1,368 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "adler2"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "320119579fcad9c21884f5c4861d16174d0e06250625266f50fe6898340abefa"
+
+[[package]]
+name = "anstream"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "824a212faf96e9acacdbd09febd34438f8f711fb84e09a8916013cd7815ca28d"
+dependencies = [
+ "anstyle",
+ "anstyle-parse",
+ "anstyle-query",
+ "anstyle-wincon",
+ "colorchoice",
+ "is_terminal_polyfill",
+ "utf8parse",
+]
+
+[[package]]
+name = "anstyle"
+version = "1.0.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "940b3a0ca603d1eade50a4846a2afffd5ef57a9feac2c0e2ec2e14f9ead76000"
+
+[[package]]
+name = "anstyle-parse"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "52ce7f38b242319f7cabaa6813055467063ecdc9d355bbb4ce0c68908cd8130e"
+dependencies = [
+ "utf8parse",
+]
+
+[[package]]
+name = "anstyle-query"
+version = "1.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "40c48f72fd53cd289104fc64099abca73db4166ad86ea0b4341abe65af83dadc"
+dependencies = [
+ "windows-sys",
+]
+
+[[package]]
+name = "anstyle-wincon"
+version = "3.0.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "291e6a250ff86cd4a820112fb8898808a366d8f9f58ce16d1f538353ad55747d"
+dependencies = [
+ "anstyle",
+ "once_cell_polyfill",
+ "windows-sys",
+]
+
+[[package]]
+name = "anyhow"
+version = "1.0.104"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "330a5ed07fa54e4702c9d6c4174f74427fc0ef6e214bbd677ae50a5099946470"
+
+[[package]]
+name = "bitflags"
+version = "2.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b588b76d00fde79687d7646a9b5bdf3cc0f655e0bbd080335a95d7e96f3587da"
+
+[[package]]
+name = "cfg-if"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
+
+[[package]]
+name = "clap"
+version = "4.6.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "473c7e07f409a8d772161724aa8db6a765a2532a70f9667eeb7b49d3d02fbdca"
+dependencies = [
+ "clap_builder",
+ "clap_derive",
+]
+
+[[package]]
+name = "clap_builder"
+version = "4.6.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7b48fea5a88e9ae728a2dcbedbfc0e730f7d60da42e1cb049a83c9fb8b789889"
+dependencies = [
+ "anstream",
+ "anstyle",
+ "clap_lex",
+ "strsim",
+]
+
+[[package]]
+name = "clap_derive"
+version = "4.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d012d2b9d65aca7f18f4d9878a045bc17899bba951561ba5ec3c2ba1eed9a061"
+dependencies = [
+ "heck",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "clap_lex"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c8d4a3bb8b1e0c1050499d1815f5ab16d04f0959b233085fb31653fbfc9d98f9"
+
+[[package]]
+name = "colorchoice"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1d07550c9036bf2ae0c684c4297d503f838287c83c53686d05370d0e139ae570"
+
+[[package]]
+name = "cpio"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "938e716cb1ade5d6c8f959c13a7248b889c07491fc7e41167c3afe20f8f0de1e"
+
+[[package]]
+name = "crc32fast"
+version = "1.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8498c871161e1742aaa9d52551b2d6ebdd4c3d45a3be423e3728f33b955be550"
+dependencies = [
+ "cfg-if",
+]
+
+[[package]]
+name = "errno"
+version = "0.3.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
+[[package]]
+name = "fastrand"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da7c62ceae207dd37ea5b845da6a0696c799f85e97da1ab5b7910be3c1c80223"
+
+[[package]]
+name = "flate2"
+version = "1.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "843fba2746e448b37e26a819579957415c8cef339bf08564fe8b7ddbd959573c"
+dependencies = [
+ "crc32fast",
+ "miniz_oxide",
+]
+
+[[package]]
+name = "getrandom"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "300e883d756b2e4ec94e02791f39b04b522276138852cfc41d9fb7e904106099"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi",
+]
+
+[[package]]
+name = "heck"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
+
+[[package]]
+name = "is_terminal_polyfill"
+version = "1.70.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a6cb138bb79a146c1bd460005623e142ef0181e3d0219cb493e02f7d08a35695"
+
+[[package]]
+name = "libc"
+version = "0.2.189"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3eaf3ede3fee6db1a4c2ee091bf8a8b4dccdc6d17f656fb07896ee72867612f2"
+
+[[package]]
+name = "linux-raw-sys"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a66949e030da00e8c7d4434b251670a91556f4144941d37452769c25d58a53"
+
+[[package]]
+name = "miniz_oxide"
+version = "0.8.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fa76a2c86f704bdb222d66965fb3d63269ce38518b83cb0575fca855ebb6316"
+dependencies = [
+ "adler2",
+ "simd-adler32",
+]
+
+[[package]]
+name = "once_cell"
+version = "1.21.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f7c3e4beb33f85d45ae3e3a1792185706c8e16d043238c593331cc7cd313b50"
+
+[[package]]
+name = "once_cell_polyfill"
+version = "1.70.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "384b8ab6d37215f3c5301a95a4accb5d64aa607f1fcb26a11b5303878451b4fe"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.107"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "985e7ec9bb745e6ce6535b544d84d6cd6f7ad8bd711c398938ae983b91a766d9"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.47"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fbf4db142a473a8d80c26bbf18454ed458bf8d26c8219c331daecfdbd079001"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "r-efi"
+version = "6.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
+
+[[package]]
+name = "rustix"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6fe4565b9518b83ef4f91bb47ce29620ca828bd32cb7e408f0062e9930ba190"
+dependencies = [
+ "bitflags",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
+]
+
+[[package]]
+name = "same-file"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "93fc1dc3aaa9bfed95e02e6eadabb4baf7e3078b0bd1b4d7b6b0b68378900502"
+dependencies = [
+ "winapi-util",
+]
+
+[[package]]
+name = "simd-adler32"
+version = "0.3.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3a219298ac11a56ea9a6d2120044824d6f01aeb034955e7af7bc16858527deea"
+
+[[package]]
+name = "slim"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "clap",
+ "cpio",
+ "flate2",
+ "tempfile",
+ "walkdir",
+ "xdg",
+]
+
+[[package]]
+name = "strsim"
+version = "0.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7da8b5736845d9f2fcb837ea5d9e2628564b3b043a70948a3f0b778838c5fb4f"
+
+[[package]]
+name = "syn"
+version = "3.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6275cddf4610d1775e6d1fe9469b2e77d0f39fd98fb7450901b821e0c53649f"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "tempfile"
+version = "3.27.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32497e9a4c7b38532efcdebeef879707aa9f794296a4f0244f6f69e9bc8574bd"
+dependencies = [
+ "fastrand",
+ "getrandom",
+ "once_cell",
+ "rustix",
+ "windows-sys",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6e4313cd5fcd3dad5cafa179702e2b244f760991f45397d14d4ebf38247da75"
+
+[[package]]
+name = "utf8parse"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "06abde3611657adf66d383f00b093d7faecc7fa57071cce2578660c9f1010821"
+
+[[package]]
+name = "walkdir"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "29790946404f91d9c5d06f9874efddea1dc06c5efe94541a7d6863108e3a5e4b"
+dependencies = [
+ "same-file",
+ "winapi-util",
+]
+
+[[package]]
+name = "winapi-util"
+version = "0.1.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c2a7b1c03c876122aa43f3020e6c3c3ee5c05081c9a00739faf7503aeba10d22"
+dependencies = [
+ "windows-sys",
+]
+
+[[package]]
+name = "windows-link"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
+
+[[package]]
+name = "windows-sys"
+version = "0.61.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
+name = "xdg"
+version = "3.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2fb433233f2df9344722454bc7e96465c9d03bff9d77c248f9e7523fe79585b5"
@@ -1,11 +1,11 @@
-use anyhow::{Context, Result};
+use anyhow::{Context, Result, bail};
 use clap::{Parser, Subcommand};
+use flate2::write::GzEncoder;
 use std::fs::{self, File};
 use std::path::{Path, PathBuf};
 use std::process::{Command, Stdio};

 #[derive(Parser, Debug)]
-#[command(name = "slim")]
 #[command(about = "Build bootable initrd VMs from container images")]
 struct Cli {
    #[command(subcommand)]
@@ -42,10 +42,53 @@ fn main() -> Result<()> {
    Ok(())
 }

-fn registry_dir(image: &str) -> PathBuf {
+/// Validate a user-supplied image name before it is used in a registry path.
+///
+/// The name becomes a directory under `$XDG_DATA_HOME/slim-rs/registry/`, so
+/// path separators and `.`/`..` would allow escaping that directory.
+/// Allow-list: ASCII alphanumerics plus `.`, `_`, `:`, `-` (covers image
+/// refs like `alpine:3.15`).
+fn validate_image_name(name: &str) -> Result<()> {
+    let valid = !name.is_empty()
+        && name != "."
+        && name != ".."
+        && name
+            .chars()
+            .all(|c| c.is_ascii_alphanumeric() || matches!(c, '.' | '_' | ':' | '-'));
+    if !valid {
+        bail!(
+            "invalid image name '{name}': must be non-empty and contain only \
+             alphanumerics, '.', '_', ':' and '-' (no path separators or '..')"
+        );
+    }
+    Ok(())
+}
+
+fn registry_dir(image: &str) -> Result<PathBuf> {
+    validate_image_name(image)?;
    let base = xdg::BaseDirectories::with_prefix("slim-rs");
-    let initrd_path = base.place_data_file(format!("registry/{}/initrd", image));
-    initrd_path.unwrap().parent().unwrap().to_path_buf()
+    let initrd_path = base
+        .place_data_file(format!("registry/{image}/initrd"))
+        .context("Failed to write to XDG_DATA_HOME")?;
+    let reg_dir = initrd_path
+        .parent()
+        .expect("data file has a parent")
+        .to_owned();
+
+    // Defense in depth: the constructed path must stay inside the registry.
+    let registry_root = base
+        .place_data_file("registry/.root-check")
+        .context("Failed to write to XDG_DATA_HOME")?
+        .parent()
+        .expect("data file has a parent")
+        .to_owned();
+    if !reg_dir.starts_with(&registry_root) {
+        bail!(
+            "invalid image name '{image}': registry path escapes {}",
+            registry_root.display()
+        );
+    }
+    Ok(reg_dir)
 }

 fn build(image: &str) -> Result<()> {
@@ -75,7 +118,7 @@ fn mount_image(image: &str) -> Result<PathBuf> {
        .context("Failed to run podman image mount")?;
    let mount_path = String::from_utf8_lossy(&output.stdout).trim().to_string();
    if !output.status.success() || mount_path.is_empty() {
-        anyhow::bail!(
+        bail!(
            "podman image mount failed: {}",
            String::from_utf8_lossy(&output.stderr).trim()
        );
@@ -95,12 +138,10 @@ fn build_artifacts(image: &str, mount_path: &Path) -> Result<()> {
        .status()
        .context("Failed to check for /vmlinuz inside the image mount")?;
    if !has_kernel.success() {
-        anyhow::bail!(
-            "Image missing required /vmlinuz. Place kernel at /vmlinuz in Containerfile."
-        );
+        bail!("Image missing required /vmlinuz. Place kernel at /vmlinuz in Containerfile.");
    }

-    let reg_dir = registry_dir(image);
+    let reg_dir = registry_dir(image)?;
    fs::create_dir_all(&reg_dir)?;
    println!("Registry: {}", reg_dir.display());

@@ -116,7 +157,7 @@ fn build_artifacts(image: &str, mount_path: &Path) -> Result<()> {
        .status()
        .context("Failed to copy vmlinuz out of the image mount")?;
    if !cp_status.success() {
-        anyhow::bail!("Failed to copy vmlinuz to registry");
+        bail!("Failed to copy vmlinuz to registry");
    }
    println!("Copied vmlinuz -> {}", vmlinuz_dst.display());

@@ -132,7 +173,7 @@ fn build_artifacts(image: &str, mount_path: &Path) -> Result<()> {
        .context("Failed to spawn the cpio pipeline")?;

    let initrd_file = File::create(&initrd_path).context("Failed to create initrd file")?;
-    let mut encoder = flate2::write::GzEncoder::new(initrd_file, flate2::Compression::default());
+    let mut encoder = GzEncoder::new(initrd_file, flate2::Compression::default());
    let cpio_stdout = cpio.stdout.take().context("cpio stdout was not piped")?;
    let copied = std::io::copy(&mut std::io::BufReader::new(cpio_stdout), &mut encoder);
    let stream_result = copied
@@ -148,7 +189,7 @@ fn build_artifacts(image: &str, mount_path: &Path) -> Result<()> {
    }
    if !cpio_status.success() {
        let _ = fs::remove_file(&initrd_path);
-        anyhow::bail!("find/cpio pipeline failed with status {cpio_status}");
+        bail!("find/cpio pipeline failed with status {cpio_status}");
    }
    println!("Created initrd -> {}", initrd_path.display());

@@ -156,11 +197,11 @@ fn build_artifacts(image: &str, mount_path: &Path) -> Result<()> {
 }

 fn run(name: &str) -> Result<()> {
-    let reg_dir = registry_dir(name);
+    let reg_dir = registry_dir(name)?;
    let vmlinuz_path = reg_dir.join("vmlinuz");
    let initrd_path = reg_dir.join("initrd");
    if !vmlinuz_path.exists() || !initrd_path.exists() {
-        anyhow::bail!(
+        bail!(
            "Registry missing vmlinuz/initrd for '{}'. Run `slim build` first.",
            name
        );
@@ -171,34 +212,77 @@ fn run(name: &str) -> Result<()> {
        vmlinuz_path.display(),
        initrd_path.display()
    );
+
+    let cmdline = [
+        "console=ttyS0,115200",
+        "root=/dev/ram0",
+        "rw",
+        "earlyprintk=serial",
+        "nokaslr",
+        "raid=noautodetect",
+    ]
+    .join(" ");
+
    // Launch with a 5-second timeout for quick smoke verification
-    let status = Command::new("timeout")
-        .args([
-            "5",
-            "qemu-system-x86_64",
-            "-m",
-            "256",
-            "-nographic",
-            "-kernel",
-            vmlinuz_path.to_str().unwrap(),
-            "-initrd",
-            initrd_path.to_str().unwrap(),
-            "-append",
-            "console=ttyS0",
-        ])
+    let status = Command::new("qemu-system-x86_64")
+        .args(["-m", "1024M"])
+        .arg("-kernel")
+        .arg(vmlinuz_path.as_os_str())
+        .arg("-initrd")
+        .arg(initrd_path.as_os_str())
+        .args(["-append", &cmdline])
+        .args(["-nographic"])
        .status()
        .context("Failed to launch qemu-system-x86_64")?;

-    // `timeout` exits 124 when it kills QEMU after the 5s smoke-test
-    // window; any other non-zero status is a real failure.
    match status.code() {
        Some(0) => println!("QEMU exited cleanly."),
-        Some(124) => println!("QEMU timed out after 5s (expected during smoke boot)."),
        Some(126) | Some(127) => {
-            anyhow::bail!("Failed to start qemu-system-x86_64 (is it installed and in PATH?)")
+            bail!("Failed to start qemu-system-x86_64 (is it installed and in PATH?)")
        }
-        Some(code) => anyhow::bail!("QEMU exited with code {code}"),
-        None => anyhow::bail!("QEMU terminated by a signal"),
+        Some(code) => bail!("QEMU exited with code {code}"),
+        None => bail!("QEMU terminated by a signal"),
    }
    Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::validate_image_name;
+
+    #[test]
+    fn accepts_valid_image_names() {
+        for name in [
+            "alpine:3.15",
+            "slim",
+            "mock-vm",
+            "my_vm",
+            "a.b.c",
+            "vm-1.2.3",
+        ] {
+            validate_image_name(name).unwrap_or_else(|e| panic!("{name} rejected: {e}"));
+        }
+    }
+
+    #[test]
+    fn rejects_traversal_and_separators() {
+        for name in [
+            "",
+            ".",
+            "..",
+            "../evil",
+            "../../tmp/evil",
+            "a/b",
+            "/abs",
+            "a\\b",
+            "foo bar",
+            "vm;rm",
+            "vm\n",
+        ] {
+            assert!(
+                validate_image_name(name).is_err(),
+                "{name:?} should be rejected"
+            );
+        }
+    }
+}