rust-harden

Rust Harden

Systematically harden the target Rust code against production failures. This is the defensive pass — every change reduces crash risk.

Preparation

1. Find the workspace root: run cargo locate-project --workspace --message-format plain 2>/dev/null | xargs dirname.
2. Identify the target: use the target argument, or default to the workspace's src/.
3. Determine if this is a library or application crate (check for lib.rs vs main.rs).

Hardening Steps

Execute these in order. For each finding, make the fix directly — don't just report it.

Step 1: Eliminate Panic Sources

Run in the shell:

rg --type rust '\.(unwrap|expect)\(' src/ --glob '!*test*' -n

For each match:

• If the unwrap is on a Result: replace with ? and add .context("description") if anyhow is available
• If the unwrap is on an Option: replace with .ok_or_else(|| Error::...) then ?
• If it's genuinely an invariant (e.g., after a length check): change to .expect("reason: invariant X holds because Y") with a clear explanation

Step 2: Document Unsafe Blocks

Run in the shell:

rg --type rust -B1 'unsafe \{' src/ -n | head -50

For each unsafe block without a preceding // SAFETY: comment, add one explaining:

• What invariant is being upheld
• Why it is safe in this context
• Under what conditions it would become unsound

Step 3: Check Overflow Protection

Read Cargo.toml and check if [profile.release] has overflow-checks = true. If not, add it:

[profile.release]
overflow-checks = true

Evidence: CVE-2018-1000810 (std str::repeat) — silent integer overflow in release build. Debug builds panic, release builds silently wrap.

Step 4: Replace Indexing with Safe Access

Run in the shell:

rg --type rust '\[\w+\]' src/ --glob '!*test*' -n | head -30

For array/slice indexing x[i] in non-test code, evaluate whether .get(i) with proper error handling is safer. Slice indexing is potentially the main source of panics in non-trivial Rust programs.