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🛡️ Sentinel: [improvement] Pre-canonicalize base path in FileSystemContext to avoid symlink escapes #245

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🛡️ Sentinel: [improvement] Pre-canonicalize base path in FileSystemContext to avoid symlink escapes #245

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4 changes: 4 additions & 0 deletions .jules/sentinel.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
## 2024-05-20 - Pre-canonicalize base path in FileSystemContext to avoid symlink escapes
**Vulnerability:** The `FileSystemContext::new` accepted an uncanonicalized base path, which could potentially lead to symlink escapes during path validation.
**Learning:** By canonicalizing the base path during construction, the check inside `secure_path` accurately determines if the target escapes the expected path, which wasn't fully guaranteed with an uncanonicalized base path.
**Prevention:** Always construct secure contexts with canonicalized paths when implementing file path validation checks, especially to prevent symlink traversal.
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11 changes: 6 additions & 5 deletions crates/services/src/lib.rs
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Expand Up @@ -142,10 +142,11 @@ pub struct FileSystemContext {
}

impl FileSystemContext {
pub fn new<P: AsRef<Path>>(base_path: P) -> Self {
Self {
base_path: base_path.as_ref().to_path_buf(),
}
pub fn new<P: AsRef<Path>>(base_path: P) -> ServiceResult<Self> {
let canonical_base = base_path.as_ref().canonicalize()?;
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@sourcery-ai sourcery-ai Bot May 19, 2026

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issue: Canonicalizing the base path in new may reject otherwise valid configurations where the directory is created later.

This constructor now requires the directory to pre-exist, so callers can’t create a context for a path that will be created later. If that scenario should remain supported, consider either delaying canonicalization until first use, or eagerly creating the directory (e.g., via create_dir_all) before canonicalizing, depending on the intended invariants.

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@sourcery-ai sourcery-ai Bot May 19, 2026

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suggestion: Consider enriching the error from canonicalize() with path context for easier debugging and observability.

Using ? here returns the bare canonicalize error, which can be hard to trace. Consider wrapping it (e.g. via a custom error variant or map_err that includes the base_path) so callers can see which base path failed when constructing different FileSystemContext roots.

Suggested implementation:

    pub fn new<P: AsRef<Path>>(base_path: P) -> ServiceResult<Self> {
        let canonical_base = base_path
            .as_ref()
            .canonicalize()
            .map_err(|e| {
                std::io::Error::new(
                    e.kind(),
                    format!(
                        "failed to canonicalize base path '{}': {}",
                        base_path.as_ref().display(),
                        e
                    ),
                )
            })?;
        Ok(Self {
            base_path: canonical_base,
        })
    }

If ServiceResult does not currently accept std::io::Error via From<std::io::Error>, you will need to:

  1. Ensure the error type used by ServiceResult implements From<std::io::Error> (or adjust the map_err to construct the appropriate service-specific error variant instead of std::io::Error::new).
  2. Optionally, if you already use a custom error type with richer context (e.g. via thiserror or anyhow::Context), replace the std::io::Error::new(...) construction with your existing pattern while keeping the base_path.as_ref().display() information in the message.

Ok(Self {
base_path: canonical_base,
})
}

/// Lexically validate path to prevent traversal attacks and symlink escapes
Expand Down Expand Up @@ -310,7 +311,7 @@ mod tests {
#[test]
fn test_file_system_context_security() {
let temp = std::env::temp_dir();
let ctx = FileSystemContext::new(&temp);
let ctx = FileSystemContext::new(&temp).unwrap();

// Valid paths
assert!(ctx.secure_path("test.txt").is_ok());
Expand Down
2 changes: 1 addition & 1 deletion crates/thread/tests/integration.rs
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Expand Up @@ -18,5 +18,5 @@ fn test_service_reexports_work() {
use thread::services::FileSystemContext;

// Just check if we can use the types
let _ctx = FileSystemContext::new(".");
let _ctx = FileSystemContext::new(".").unwrap();
}