git:20260913.4c35c60 to git:20260913.46c999d

---

name: race-condition

description: Classify race condition evidence — TOCTOU (access→fopen), shared-state (lock→unlock→mutate), and classic shared-variable data races in pthread code. Maps to CWE-362.

license: MIT

compatibility: opencode,claude code,DSH

metadata:

cwe: CWE-362

severity: HIGH

domain: concurrency

---

## Race Condition Analysis (CWE-362)

### Evidence Patterns

#### TOCTOU: Filesystem (CWE-362)

- **RACE_CONDITION event** with category `toctou`

- Pattern: `access(path, ...)` check followed by `fopen(path, ...)` / `open(path, ...)`

- Time-of-check to time-of-use window allows symlink attack or file swap

#### TOCTOU: Shared State (CWE-362)

- **RACE_CONDITION event** with category `toctou_shared_state`

- Pattern: `mutex_lock` → `check` → `mutex_unlock` → `mutate`

- Check and mutation not atomic; another thread can change state between unlock and mutate

#### Classic Data Race (CWE-362)

- **RACE_CONDITION event** with category `shared_data_race`

- Pattern: a file-scope variable accessed by two or more `pthread_create` thread functions, with at least one write, and no `pthread_mutex_lock`/`unlock` scope around the access

- Examples: `g_shared_counter++` in two threads, writer/reader pairs on `g_flag`/`g_data`

- The event carries `thread_functions`, `thread_instances` and `write_line` properties

### Safe Patterns (P0 Exclusion)

| Safe Pattern | Why Safe |

|---------------|----------|

| `fopen(path, "r")` directly, check result | No check-then-use window |

| `open(path, O_RDONLY | O_NOFOLLOW)` | Rejects symlinks atomically |

| `fstat(fd, &st)` after `open` | Check on the fd, not the path |

| Lock held through both check and mutation | Atomic check-then-act |

### Classification Rules

| Condition | Classification |

|-----------|---------------|

| `access()` + `fopen()` on same path, no atomicity | **confirmed** |

| `access()` + `open()` with `O_NOFOLLOW` | **false-positive** |

| Mutate a shared/global variable after releasing a lock | **suspected** (a TOCTOU only if the same variable was READ inside the lock — verify the check-then-act pair) |

| Lock held through check + mutate | **false-positive** |

| `access()` + `fopen()` in same function, path is local | **suspected** (may be safe if path not attacker-controlled) |

| Check-then-act with no shared state | **false-positive** |

| Shared variable, >= 2 pthread threads, >= 1 write, no lock | **confirmed** |

| Shared variable, all accesses inside lock scope | **false-positive** |

| Shared variable accessed by only one thread function | **false-positive** (no concurrent access) |

### Fix Suggestions

- Replace `access()` + `fopen()` with direct `fopen()` and error check

- Use `open()` with `O_NOFOLLOW` to reject symlinks

- Hold the mutex through both check and mutation (don't unlock between)

- Use `fstat()` on the fd instead of `stat()` on the path

- For file locking, use `flock()` or `fcntl(F_SETLK)` for atomic lock+check

- Consider single-threaded design for simple cases