feat(pool,wpf): bare-owner using dangle + one-hop indirect field-UAF → OWN002

.github/workflows/ci.yml

@@ -796,11 +796,15 @@ jobs:
         # leak / double-dispose ride the flow (POOL001/003 — `memorypool-double-dispose` -> OWN003), and
         # its `owner.Memory` / `owner.Memory.Span` view is a borrow lowered to a use of the OWNER
         # (`ViewOwner`), so reading it after Dispose trips OWN002 (POOL002 — `memorypool-view-after-
-        # dispose`). A FIELD-mediated cross-method use-after-dispose is caught too: an IDisposable field
-        # disposed in `Dispose()` and DIRECTLY read (`_field.Member`) in a live subscription-target handler
-        # (RHS of a `+=` / arg of a `.Subscribe(...)`, not torn down, no `if (_disposed) return;` guard) is
-        # lowered to a synthetic acquire/release/use flow -> OWN002 (`field-use-after-dispose`). Remaining
-        # backlog: a view stored in a FIELD, an INDIRECT (helper-mediated) field use after dispose, and an
-        # injected-source region-escape. A drop below the floor is a regression.
-        run: python scripts/benchmark.py --min-recall 20
+        # dispose`). Returning the BARE owner under `using` (`using owner = …; return owner;`) is the twin
+        # of the returned-view dangle: the using-owner stays tracked through the bare return (a non-using
+        # transfer does not) and its use is threaded after the scope-exit release -> OWN002 (`memorypool-
+        # using-owner-escape`). A FIELD-mediated cross-method use-after-dispose is caught too: an IDisposable
+        # field disposed in `Dispose()` and read in a live subscription-target handler (RHS of a `+=` / arg
+        # of a `.Subscribe(...)`, not torn down, no `if (_disposed) return;` guard) — DIRECTLY
+        # (`field-use-after-dispose`) or ONE hop down through a private helper (`handler-use-after-dispose`)
+        # — lowered to a synthetic acquire/release/use flow -> OWN002. Remaining backlog: a view stored in a
+        # FIELD, a TWO-plus-hop indirect field use, and an injected-source region-escape. A drop below the
+        # floor is a regression.
+        run: python scripts/benchmark.py --min-recall 22
 

corpus/real-world/memorypool-using-owner-escape/after.cs

@@ -0,0 +1,15 @@
+// AFTER (fixed). Ownership is TRANSFERRED to the caller: no `using`, so the owner is NOT disposed at
+// scope exit — the method hands back a live `IMemoryOwner<T>` and the caller owns its lifetime
+// (disposes it when done). A bare owner returned WITHOUT `using` is a genuine ownership transfer, so
+// the flow pass does not track it and the checker stays silent.
+using System;
+using System.Buffers;
+
+static class MemoryPoolUsingOwnerEscape
+{
+    static IMemoryOwner<byte> Borrow(int n)
+    {
+        IMemoryOwner<byte> owner = MemoryPool<byte>.Shared.Rent(n);   // no `using` -> transfer
+        return owner;   // caller owns and disposes it
+    }
+}

corpus/real-world/memorypool-using-owner-escape/before.cs

@@ -0,0 +1,21 @@
+// BEFORE (buggy). The bare-owner `using` dangle — the twin of `memorypool-using-view-escape`. An
+// `IMemoryOwner<T>` from `MemoryPool<T>` is held with a `using` declaration — so it is `Dispose()`d
+// at scope exit — but the method RETURNS THE OWNER ITSELF. The implicit dispose runs as the method
+// returns, so the caller receives an `IMemoryOwner<T>` already disposed (its pooled buffer handed
+// back to the pool): a dangling owner / use-after-free. `using owner = …; return owner;` is exactly
+// `try { return owner; } finally { owner.Dispose(); }`. The fix TRANSFERS ownership: drop the
+// `using` and let the caller own and dispose it (see after.cs).
+//
+// Wrapped in a class so the extractor's per-class flow pass visits it.
+using System;
+using System.Buffers;
+
+static class MemoryPoolUsingOwnerEscape
+{
+    static IMemoryOwner<byte> Borrow(int n)
+    {
+        using IMemoryOwner<byte> owner = MemoryPool<byte>.Shared.Rent(n);
+        return owner;   // <-- BUG: the `using` disposes owner as we return, so the caller gets an
+                        //     IMemoryOwner already returned to the pool
+    }
+}

corpus/real-world/memorypool-using-owner-escape/case.own

@@ -0,0 +1,16 @@
+// OwnLang model of the MemoryPool bare-owner `using` escape. `acquire` == MemoryPool.Rent,
+// `release` == the implicit `using` scope-exit Dispose. The method returns the OWNER itself, but
+// the `using` disposes it FIRST (the extractor desugars `using owner = …; return owner;` to
+// `acquire; release; use` — the returned owner is read by the caller AFTER Dispose), so the caller
+// holds an `IMemoryOwner` already returned to the pool: a use-after-release lowered to OWN002. The
+// bare-owner twin of `memorypool-using-view-escape` (which returns `owner.Memory`, a view of it).
+module Corpus
+resource MemoryOwner {
+  acquire Rent
+  release Dispose
+}
+fn lease(n: int) {
+  let owner = acquire MemoryOwner(n);   // using MemoryPool.Rent
+  release owner;                        // implicit `using` Dispose at scope exit
+  use owner;                            // return owner — read by the caller AFTER Dispose -> OWN002
+}

corpus/real-world/memorypool-using-owner-escape/expected-diagnostics.txt

@@ -0,0 +1 @@
+OWN002

corpus/real-world/memorypool-using-owner-escape/notes.md

@@ -0,0 +1,30 @@
+# MemoryPool bare-owner `using` escape (`using owner = …; return owner;`)
+
+**Pattern:** an `IMemoryOwner<T>` from `MemoryPool<T>` is held with a `using` declaration (so it is
+`Dispose()`d at scope exit), but the method **returns the owner itself**. The implicit dispose runs
+as the method returns, so the caller receives an `IMemoryOwner<T>` whose pooled buffer has already
+been handed back to the pool — a dangling owner / use-after-free. It is exactly
+`try { return owner; } finally { owner.Dispose(); }` — the **bare-owner** twin of the returned-view
+dangle (`memorypool-using-view-escape`, which returns `owner.Memory`). The fix is to **transfer
+ownership**: drop the `using` and return the live owner so the caller owns its lifetime.
+
+**Why it was missed before (Codex follow-up on #74):** a local that is `return`ed is treated as an
+ownership transfer (the caller's to release) and dropped from the tracked set — so the bare-owner
+return escaped and was never analysed, even though the `using` makes it a dangle rather than a
+transfer. This slice keeps a **`using`-declared MemoryPool owner that is returned bare** tracked
+(only this shape is exempted from the return-escape — a non-`using` returned owner stays a genuine
+transfer, untracked, silent), and threads a use of the returned owner after the `using`-desugar's
+scope-exit release — reusing the exact return-chain insertion that already catches the returned
+**view** (`memorypool-using-view-escape`). So the caller's use of the owner lands after the release
+and trips OWN002.
+
+**What the checker says:** the OwnLang model and the real `before.cs` both trip **OWN002**. The
+ownership-transfer fix in `after.cs` returns the owner with no `using`, so the escaped owner is
+untracked and the checker is silent.
+
+**Honesty / scope.** `case.own` is a faithful hand reduction (not C# ingested by the checker);
+`before.cs` / `after.cs` are representative of the bug and its fix. One escape vector each: this
+catches the bare OWNER return; `memorypool-using-view-escape` catches the returned VIEW.
+
+Reference: [P-007](../../../docs/proposals/P-007-arraypool-span.md); the view twin is
+`memorypool-using-view-escape` (#73/#74).

corpus/wpf/handler-use-after-dispose/after.cs

@@ -1,13 +1,19 @@
-// FIXED. The callback guards on the disposed flag (and/or the subscription is
-// disposed only after the dispatcher queue is drained), so nothing touches the
-// subscription-backed state after Dispose().
+// FIXED. The callback guards on the disposed flag BEFORE it calls the helper, so a late, already-
+// dispatched callback bails before anything reaches the connection. (Equivalently, drain the
+// dispatcher queue before disposing.) The extractor's field-UAF pass sees the opening
+// `if (_disposed) return;` guard precede the helper call and stays silent.
+using System;
+using System.Data.SqlClient;
+
 public sealed class CustomerViewModel : IDisposable
 {
     private readonly IDisposable _sub;
+    private readonly SqlConnection _conn;
     private bool _disposed;
 
     public CustomerViewModel(IEventBus bus)
     {
+        _conn = new SqlConnection("Server=.;Database=Customers");
         _sub = bus.Subscribe<CustomerChanged>(OnCustomerChanged);
     }
 
@@ -17,11 +23,23 @@ private void OnCustomerChanged(CustomerChanged e)
         Refresh();
     }
 
-    private void Refresh() { /* ... */ }
+    private void Refresh()
+    {
+        _conn.ChangeDatabase("customers");
+    }
 
     public void Dispose()
     {
         _disposed = true;
         _sub.Dispose();
+        _conn.Dispose();
     }
 }
+
+// Minimal in-file stand-ins so the reduction is self-contained.
+public interface IEventBus
+{
+    IDisposable Subscribe<T>(Action<T> handler);
+}
+
+public sealed class CustomerChanged { }

corpus/wpf/handler-use-after-dispose/before.cs

@@ -1,29 +1,49 @@
-// BUGGY (representative WPF pattern, hand-reduced into case.own).
+// BUGGY (representative WPF pattern; the C# extractor now catches this end-to-end via its one-hop
+// indirect field-UAF pass).
 //
-// The VM disposes its subscription on close, but a callback that was already
-// queued on the dispatcher still runs and touches the (now disposed) state. In
-// real code this surfaces as an ObjectDisposedException or a read of torn state.
+// The VM disposes its subscription (and its owned connection) on close, but a callback already
+// queued on the dispatcher still runs after Dispose() and reaches the disposed connection
+// INDIRECTLY: the handler calls a private `Refresh()` helper that reads `_conn` (disposed in
+// Dispose()). In real code this surfaces as an ObjectDisposedException or a read of torn state.
+// Unlike `field-use-after-dispose` (a DIRECT `_conn.X` read in the handler), here the disposed field
+// is one hop down, behind the helper — the extractor chases that single hop. The fix (after.cs)
+// guards the handler on a disposed flag before it calls the helper.
+using System;
+using System.Data.SqlClient;
+
 public sealed class CustomerViewModel : IDisposable
 {
     private readonly IDisposable _sub;
-    private bool _disposed;
+    private readonly SqlConnection _conn;
 
     public CustomerViewModel(IEventBus bus)
     {
+        _conn = new SqlConnection("Server=.;Database=Customers");
         _sub = bus.Subscribe<CustomerChanged>(OnCustomerChanged);
     }
 
     private void OnCustomerChanged(CustomerChanged e)
     {
         // a late, already-dispatched callback: runs after Dispose()
-        Refresh();   // touches subscription-backed state after it was disposed
+        Refresh();   // reaches the disposed _conn INDIRECTLY (one hop, through the helper)
     }
 
-    private void Refresh() { /* reads disposed state */ }
+    private void Refresh()
+    {
+        _conn.ChangeDatabase("customers");   // <-- reads the disposed connection
+    }
 
     public void Dispose()
     {
-        _disposed = true;
         _sub.Dispose();
+        _conn.Dispose();
     }
 }
+
+// Minimal in-file stand-ins so the reduction is self-contained.
+public interface IEventBus
+{
+    IDisposable Subscribe<T>(Action<T> handler);
+}
+
+public sealed class CustomerChanged { }

corpus/wpf/handler-use-after-dispose/case.own

@@ -1,17 +1,19 @@
+// OwnLang model of the field-mediated use-after-dispose reached INDIRECTLY (through a helper).
+// `acquire` == the owned connection's construction, `release` == its Dispose() in the ViewModel's
+// Dispose(), `use` == a late dispatcher callback (the subscribed handler) reaching the connection
+// one hop down — via a private Refresh() helper — AFTER Dispose(). Using a disposable after its
+// release is the generic OWN002, tagged with the resource kind. The indirect twin of
+// `field-use-after-dispose` (a DIRECT field read); the extractor now chases the single helper hop.
 module WpfHandlerAfterDispose
 
-// Same subscription-token protocol, tagged with its kind.
-resource Subscription {
-    acquire Subscribe
+resource Connection {
+    acquire Open
     release Dispose
-    kind "subscription token"
+    kind "disposable"
 }
 
-// On window close the VM disposes (unsubscribes) its subscription, but a late
-// queued callback still touches it. Using a subscription after Dispose is the
-// generic use-after-release (OWN002), tagged with the resource kind.
-fn CloseHandler(bus: int) {
-    let sub = acquire Subscription(bus);
-    release sub;          // unsubscribed / disposed on close
-    use sub;              // a late callback still touches it -> OWN002
+fn OnCustomerChanged(bus: int) {
+    let conn = acquire Connection(bus);
+    release conn;   // ViewModel.Dispose() disposes the owned connection
+    use conn;       // a late callback reaches it via Refresh() after Dispose -> OWN002
 }

corpus/wpf/handler-use-after-dispose/notes.md

@@ -1,25 +1,32 @@
-# WPF subscription used after Dispose
+# WPF field-use-after-dispose reached INDIRECTLY (through a helper)
 
-**Pattern:** a ViewModel unsubscribes / disposes its subscription on close, but a
-callback that was already queued on the dispatcher still runs and touches the
-disposed, subscription-backed state. In real code this is an
-`ObjectDisposedException` or a read of torn state — the use-after-dispose cousin
+**Pattern:** a ViewModel owns an `IDisposable` (here a `SqlConnection`) and subscribes a handler to
+an event source. On teardown `Dispose()` disposes the connection (and the subscription token), but a
+callback already queued on the dispatcher still runs after `Dispose()` and reaches the disposed
+connection **indirectly** — the handler calls a private `Refresh()` helper that reads `_conn`. In
+real code this is an `ObjectDisposedException` or a read of torn state — the use-after-dispose cousin
 of the zombie-ViewModel leak.
 
-**What the checker says:** using a resource after its `release` (Dispose) is the
-generic **OWN002** (use after release), carrying the resource-kind tag:
+**What's new — the extractor catches the one hop.** The Roslyn extractor's field-mediated
+use-after-dispose pass (under `--flow-locals`) already caught a **direct** `_field.Member` read in a
+live handler (`field-use-after-dispose`). This slice chases a **single hop**: a subscribed handler
+that calls a **private same-class helper** (`Refresh()` / `this.Refresh()`) which itself
+*unguardedly* reads a disposed field — with no `if (_disposed) return;` guard before the call — is
+lowered to a synthetic `acquire`/`release`/`use` flow → **OWN002**, via the existing OwnIR bridge
+(no new diagnostic). On the real C# the `corpus-benchmark` job scores `before.cs` as caught and
+`after.cs` (the guarded fix) as silent.
 
-```text
-$ python -m ownlang check corpus/wpf/handler-use-after-dispose/case.own
-case.own:16:9: error: [OWN002] use 'sub' after it was released
-  [resource: subscription token]
-  16 |     use sub;
-               ^
-```
+**Precision (why it stays low-FP).** One hop only — a deeper chain stays an honest miss. The helper
+must be a **private instance** method (not a public/virtual member with a broader contract); both the
+handler (before the call) and the helper must lack a disposed-guard; and the field read is a
+**direct** `this`-owned `_field.Member`. The guard exclusion is the canonical fix, so the guarded
+`after.cs` is silent.
 
-**Honesty / scope.** `case.own` is a *hand reduction* of the C# pattern, not
-direct C# extractor output (the C# extractor in P-001 is narrow — event
-subscriptions only). It shows the ownership
-*logic* maps onto the real bug; it does not model the dispatcher queue or
-exception flow. `before.cs` / `after.cs` are representative, not a verbatim copy
-of one PR.
+**Honesty / scope.** This catches the **direct** read (`field-use-after-dispose`) and now the
+**one-hop indirect** read (this case). A two-plus-hop chain, or a read through a field/property
+indirection, remains an honest extractor miss — the `case.own` reduction still fires OWN002, showing
+the ownership logic maps onto the real bug. `before.cs` / `after.cs` are representative of the bug
+and its fix.
+
+Reference: [P-007](../../../docs/proposals/P-007-arraypool-span.md); the direct twin is
+`field-use-after-dispose`; the late-callback framing matches `zombie-viewmodel`.