From 3a47e14cbe6e15de0758c8bd4233a8d84ff80aa8 Mon Sep 17 00:00:00 2001
From: Hermes Agent <hermes@localhost>
Date: Wed, 12 Aug 2026 05:12:40 +0000
Subject: Reject archive outputs inside rootfs

---
 src/archive.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

(limited to 'src')

diff --git a/src/archive.rs b/src/archive.rs
index 9a899bf..ad424c4 100644
--- a/src/archive.rs
+++ b/src/archive.rs
@@ -26,6 +26,7 @@ impl NativeTarWriter {
         }
 
         let output = output.as_ref();
+        reject_output_inside_rootfs(rootfs, output)?;
         let temporary = temporary_output_path(output)?;
         let result = (|| {
             let file = OpenOptions::new()
@@ -53,6 +54,24 @@ impl NativeTarWriter {
     }
 }
 
+fn reject_output_inside_rootfs(rootfs: &Path, output: &Path) -> Result<()> {
+    let rootfs = rootfs
+        .canonicalize()
+        .with_context(|| format!("canonicalize rootfs {}", rootfs.display()))?;
+    let output_parent = output.parent().unwrap_or_else(|| Path::new("."));
+    let output_parent = output_parent
+        .canonicalize()
+        .with_context(|| format!("canonicalize archive output parent {}", output_parent.display()))?;
+    if output_parent.starts_with(&rootfs) {
+        bail!(
+            "archive output must not be inside rootfs: {} is below {}",
+            output.display(),
+            rootfs.display()
+        );
+    }
+    Ok(())
+}
+
 fn temporary_output_path(output: &Path) -> Result<PathBuf> {
     let name = output
         .file_name()
-- 
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