Secure by Design: 10-Day Proven Memory-Safe Sprint

7 min read3 days ago

If you’re serious about secure by design, you don’t need a six-month rewrite. You need a focused 10-day sprint that shrinks memory-safety risk fast — without breaking product roadmaps.

This post turns guidance into action: we’ll target hot-path modules, wrap unsafe calls, stage Rust/Go FFI, ship CI checks that block regressions, and publish a minimal ADR + “paved-road” repo for teams to copy. You’ll also get sample PRs, rollout traps to avoid, and real code you can paste today.

Secure by Design: 10-Day Proven Memory-Safe Sprint

Want everything in one bundle? Get the Memory-Safe Sprint Kit (checklists + sample PRs) — and we’ll tailor it to your stack. Start with our Risk Assessment Services and move straight into Remediation Services to accelerate the rollout.

What “Secure by Design” means in practice

Memory-safe roadmap: remove or encapsulate UB (undefined behavior), unify allocators, and make safety automatic via CI.
Contain blast radius: fence off legacy C/C++ behind stable C ABI wrappers; migrate module-by-module.
Prove it: sanitizers, fuzzers, and policy gates that fail builds if unsafe creep returns.

While you migrate, keep your external attack surface honest — run a quick sweep with our Website Vulnerability Scanner to catch HTTP header gaps, exposed files, and common misconfigurations. (Perfect for weekly checks during the sprint.)

Free Website Vulnerability Scanner (Hero + Features)

Screenshot of the free tools webpage where you can access security assessment tools.

10-Day Memory-Safe Migration Sprint (day-by-day)

Day 1 — Choose scope & guardrails

Pick 1–2 hot-path modules (crashers, ASan hits, or code with recurring CVEs).
Set org-wide guardrails:
Disallow new unsafe except behind ffi/ or intrinsics/.
Gate builds with sanitizers on debug and Miri/Geiger in CI (see below).

Day 2 — Map interfaces & allocators

Inventory all cross-module boundaries.
Decide allocator policy: one owner for alloc/free across FFI (*no mixed allocators*).
Write the ADR: why FFI + increment over rewrite; rollback plan.

Day 3 — C ABI wrappers (stabilize the edges)

Create a thin C layer that normalizes types/ownership. Example for a “tokenize” library:

tokenize.h (C ABI)

// tokenize.h
#pragma once
#include <stddef.h>
#ifdef __cplusplus
extern "C" {
#endif

typedef struct {
  const char* ptr;
  size_t len;
} c_slice;
// Opaque handle to tokenizer instance.
typedef struct tokenizer tokenizer_t;
tokenizer_t* tokenizer_new(void);
void tokenizer_free(tokenizer_t* t);
// Input is a UTF-8 buffer; output is allocated by callee.
// Caller must call tokens_free() with the same allocator.
int tokenize(tokenizer_t* t, c_slice input, int** out_tokens, size_t* out_len);
// Memory management (single allocator boundary!)
void* ms_alloc(size_t n);
void ms_free(void* p);
void tokens_free(int* p);
#ifdef __cplusplus
}
#endif

Day 4 — Rust core with safe wrappers

lib.rs (Rust, FFI-safe)

#![deny(unsafe_op_in_unsafe_fn)]
use std::{ffi::c_int, ptr::null_mut, slice};

#[repr(C)]
pub struct c_slice { pub ptr: *const u8, pub len: usize }
#[repr(C)]
pub struct tokenizer_t { inner: tokenizer::Tokenizer }
#[no_mangle]
pub extern "C" fn tokenizer_new() -> *mut tokenizer_t {
    Box::into_raw(Box::new(tokenizer_t { inner: tokenizer::Tokenizer::default() }))
}
#[no_mangle]
pub unsafe extern "C" fn tokenizer_free(p: *mut tokenizer_t) {
    if !p.is_null() { drop(Box::from_raw(p)); }
}
#[no_mangle]
pub unsafe extern "C" fn tokenize(
    t: *mut tokenizer_t,
    input: c_slice,
    out_tokens: *mut *mut c_int,
    out_len: *mut usize,
) -> c_int {
    if t.is_null() || input.ptr.is_null() || out_tokens.is_null() || out_len.is_null() { return -1; }
    let bytes = slice::from_raw_parts(input.ptr, input.len);
    let tokens = (*t).inner.tokenize(bytes);
    let len = tokens.len();
    let buf = ms_alloc(len * std::mem::size_of::<c_int>()) as *mut c_int;
    if buf.is_null() { return -2; }
    // Copy safely
    for (i, tok) in tokens.iter().enumerate() {
        unsafe { *buf.add(i) = *tok as c_int; }
    }
    unsafe { *out_tokens = buf; *out_len = len; }
    0
}
#[no_mangle]
pub extern "C" fn tokens_free(p: *mut c_int) { unsafe { ms_free(p as *mut _) } }
// Provided by the C layer (single allocator source of truth)
extern "C" {
    fn ms_alloc(n: usize) -> *mut std::ffi::c_void;
    fn ms_free(p: *mut std::ffi::c_void);
}

Key takeaways

#[repr(C)] for FFI types.
One allocator via ms_alloc/ms_free—no mixed allocators across languages.
All unsafe is corralled to tiny FFI functions; core logic is safe Rust.

Day 5 — Go or C++ callers (real usage)

Go (cgo) caller

// go:build cgo
package tok

// #cgo CFLAGS: -I./cabi
// #cgo LDFLAGS: -L${SRCDIR}/target/debug -ltokenize
// #include "tokenize.h"
import "C"
import "unsafe"
type Tokenizer struct { ptr *C.tokenizer_t }
func New() *Tokenizer { return &Tokenizer{C.tokenizer_new()} }
func (t *Tokenizer) Close() { C.tokenizer_free(t.ptr) }
func (t *Tokenizer) Tokens(b []byte) ([]int32, error) {
    var out *C.int
    var n C.size_t
    in := C.c_slice{ptr: (*C.uchar)(unsafe.Pointer(&b[0])), len: C.size_t(len(b))}
    if rc := C.tokenize(t.ptr, in, &out, &n); rc != 0 { return nil, fmt.Errorf("rc=%d", rc) }
    defer C.tokens_free(out)
    // copy to Go slice
    sl := unsafe.Slice(out, n)
    res := make([]int32, n)
    for i, v := range sl { res[i] = int32(v) }
    return res, nil
}

CMake (sanitizers on by default in dev)

# CMakeLists.txt
if(NOT CMAKE_BUILD_TYPE)
  set(CMAKE_BUILD_TYPE Debug)
endif()
add_compile_options(-fno-omit-frame-pointer -fsanitize=address,undefined)
add_link_options(-fsanitize=address,undefined)

Day 6 — Safety nets: fuzz, sanitize, miri

Fuzz Rust core with cargo fuzz on exported pure functions.
Run AddressSanitizer/UBSan on the C/C++ wrapper (see above).
Add Miri to shake out UB in unsafe blocks.

GitHub Actions (Rust + C gates)

name: memory-safe-gates
on: [push, pull_request]
jobs:
  rust-ci:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: dtolnay/rust-toolchain@stable
      - run: cargo fmt -- --check
      - run: cargo clippy -- -D warnings
      - run: cargo test
      - run: cargo miri test -- -Zmiri-strict-provenance
      - run: cargo install cargo-geiger && cargo geiger -q --include-tests

c-ci:
    runs-on: ubuntu-latest
    env: { ASAN_OPTIONS: detect_leaks=1 }
    steps:
      - uses: actions/checkout@v4
      - run: sudo apt-get update && sudo apt-get install -y cmake clang
      - run: cmake -S . -B build && cmake --build build && ctest --test-dir build

Day 7 — Replace foot-guns with safe shims

Ban raw char* ownership transfers; use c_slice + explicit free.
Standardize error codes; move to Result<T, E> internally.
Add safer_ffi-style helpers or hand-rolled thin wrappers to reduce unsafe surface.

Day 8 — Instrument & measure the burn-down

Track:

Crash rate (per K sessions).
ASan/UBSan findings (open → closed).
Unsafe LOC (via cargo geiger) and C/C++ LOC retired.

Day 9 — Stage rollout

Dark-ship the Rust/Go core behind a feature flag.
Stress-test with production payloads in a canary.
Collect perf deltas (+/- CPU, p95 latency, RSS).

Day 10 — Publish the “paved road”

Minimal ADR (problem, options, decision, consequences).
“Copy-this” repo template: ffi/, abi/, rust/, cxx/, ci/.
Add a short coding standard: lifetime rules, allocator rules, logging, error codes.

Sample Report to check Website Vulnerability (Headers + Exposed Files)

Sample vulnerability assessment report generated with our free tool, providing insights into possible vulnerabilities.

Sample PR (ready to paste)

Title: Replace C tokenizer core with Rust (FFI), unify allocators

Why: Crash rate 3.7/K sessions traced to tokenizer; ASan shows UAF in trie_update().
What changed:
- Introduced Rust core (crate `tokenizer`), exported via C ABI in `abi/tokenize.h`.
- All allocation unified via ms_alloc/ms_free; removed malloc/free from caller.
- Added CI gates: cargo miri, geiger, ASan/UBSan, clippy – PR blocks on red.
- Added fuzz target `fuzz_tokenize_identifiers`.
Risk/rollout:
- Behind `TOK_RUST=1` env flag. Gradual 10% canary.
- Rollback: set TOK_RUST=0, revert to C implementation.
Testing:
- 126 unit tests (Rust), 32 integration tests (C).
- Fuzz: 5m @ 20k exec/s, no new crashes.
- Perf: p95 -11% latency, RSS -6% in canary.

Real-world pitfalls (and how to dodge them)

Mixed allocators across FFI → standardize on one allocator and provide *_free helpers.
Dangling slices to Rust from C → only accept c_slice with explicit length; copy immediately.
ABI drift (struct layout) → freeze types with #[repr(C)] and bump SONAME on breaking changes.
UTF-8 assumptions → validate and return an error code; do not transmute blindly.
“Temporary unsafe” creep → CI gates + #![deny(unsafe_op_in_unsafe_fn)] + codeowners on ffi/.

CI policies that make safety stick

Pre-commit (dev machines)

# .pre-commit-config.yaml
repos:
- repo: https://github.com/rust-lang/rustfmt
  rev: stable
  hooks: [{id: rustfmt}]
- repo: https://github.com/rust-lang/rust-clippy
  rev: stable
  hooks: [{id: clippy}]
- repo: local
  hooks:
    - id: clang-tidy
      name: clang-tidy
      entry: bash -lc 'clang-tidy **/*.c **/*.cpp'
      language: system

Block PRs if:

New unsafe outside ffi/ or intrinsics/.
Sanitizer build fails or Miri finds UB.
Geiger reports increased unsafe usage.

Add a paved-road repo layout

/abi          # C headers, stable ABI, versioned
/ffi          # thin language bindings, safety shims
/rust         # safe core crate(s)
/cxx          # legacy C/C++ (shrinking)
/ci           # workflow files, sanitizer configs
/tools        # fuzzers, scripts
/docs         # ADRs, migration notes

“Secure by design” beyond code: quick wins you can ship today

External exposure sweep each week of the sprint with our Free Website Vulnerability Scanner (HTTP headers, exposed files, common web risks). Drop the CSV findings into your risk register and prove progress.
→ Try it now: free.pentesttesting.com (no signup).
Need executive sign-off and a clear path from findings → fixes? Start with a quick consult via our Risk Assessment Services and roll directly into Remediation Services for prioritized closures.
Our Cybersecurity Blog: https://www.pentesttesting.com/blog/