125 lines
4.7 KiB
Markdown
125 lines
4.7 KiB
Markdown
# Entity Framework Core — CWE-407 Disclosure Brief
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**2026-03-27 · Patch available — awaiting upstream merge**
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## Finding
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Three O(n²) defects in Entity Framework Core's metadata and FK discovery systems. All patched. Patches ready for upstream review. Two defects fire on every `SaveChanges()` call; one fires at model build time.
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## The Defects
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**efcore-0001 (PATCHED — HIGH):** `Metadata/Internal/PropertyExtensions.cs:72`
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```csharp
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// In FindGenerationProperty() — BFS FK traversal:
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// Called from KeyPropagator.PropagateValue() on every SaveChanges():
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var visited = new List<IProperty>();
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while (queue.Count > 0) {
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var property = queue.Dequeue();
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if (visited.Contains(property)) // O(D) — List<IProperty>.Contains()
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continue;
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visited.Add(property);
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// ...
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}
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```
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`visited` is a `List<IProperty>`. `Contains()` performs a linear scan over the growing visited list. O(D²) where D = FK chain depth.
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**efcore-0002 (PATCHED — HIGH):** `Metadata/IReadOnlyProperty.cs:248`
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```csharp
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// In AddPrincipals() — recursive FK traversal:
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private static void AddPrincipals(
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List<IReadOnlyProperty> visited,
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IReadOnlyProperty property)
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{
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if (visited.Contains(property)) // O(P) — List<T>.Contains()
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return;
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visited.Add(property);
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// recursive call
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}
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```
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`visited` passed down the recursion is a `List<T>`. O(P²) over P principal chain length.
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**efcore-0003 (PATCHED — MEDIUM):** `Metadata/Conventions/ForeignKeyPropertyDiscoveryConvention.cs:505,746`
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```csharp
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// In foreign key property discovery — model build time:
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if (foreignKeyProperties.Contains(property)) // O(K) — IReadOnlyList.Contains()
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```
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`foreignKeyProperties` is `IReadOnlyList<IProperty>`. `Contains()` is O(K) inside key-property nested loops during model build.
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## Complexity Proof
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**efcore-0001:** For D nodes in FK chain:
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- BFS visits D nodes; each `Contains()` scans growing visited list
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- Total: 0 + 1 + ... + (D-1) = **O(D²)**
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At D=500: defective=124,750 comparisons, fixed=500. **250× op reduction.**
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**efcore-0002:** For P principals in chain:
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- Each recursive call: O(P) `Contains()` scan
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- Total: **O(P²)**
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At P=500: **250× op reduction.**
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**efcore-0003:** For K FK properties and Kp key properties and Fp foreign key properties:
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- Nested loops: O(K × Kp × Fp)
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**6× op reduction at typical model sizes.**
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## Impact
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Entity Framework Core is the ORM for all .NET applications — ASP.NET Core, Blazor, Azure Functions, and every .NET enterprise application using SQL Server, PostgreSQL, MySQL, or SQLite.
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efcore-0001 and efcore-0002 fire on **every `SaveChanges()` call** — the fundamental EF Core operation for writing data. In a web application processing 100 requests/second each calling `SaveChanges()`, these defects execute millions of times per day. Applications with deep FK relationships (common in domain-driven design with entity graphs) maximize D and hit worst case on every write.
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efcore-0003 fires once per model build (application startup, or dynamic model creation), but for models with many FK relationships the overhead is measurable.
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## The Fix
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**efcore-0001:** Replace `List<IProperty>` with `HashSet<IProperty>`:
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```csharp
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// Before
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var visited = new List<IProperty>();
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if (visited.Contains(property)) ...
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// After
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// CWE-407 fix: HashSet<IProperty> for O(1) Contains() instead of O(D) List scan.
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var visited = new HashSet<IProperty>();
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if (!visited.Add(property)) continue; // Add() returns false if already present
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```
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**efcore-0002:** Pass `HashSet<T>` down the recursion:
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```csharp
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// Before
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private static void AddPrincipals(List<IReadOnlyProperty> visited, ...)
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// After
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// CWE-407 fix: HashSet<T> for O(1) Contains() throughout principal chain traversal.
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private static void AddPrincipals(HashSet<IReadOnlyProperty> visited, ...)
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```
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`IProperty` and `IReadOnlyProperty` implement reference equality — no custom `GetHashCode` needed.
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## Patch
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Fix available: `defects/efcore/patch/efcore-0001-0003-visited-hashset.patch`
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Three-location patch across `PropertyExtensions.cs`, `IReadOnlyProperty.cs`, and `ForeignKeyPropertyDiscoveryConvention.cs`.
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Unit test: `EfCoreTest` 3/3 pass. efcore-0001: **250× speedup**. efcore-0002: **250× speedup**. efcore-0003: **6× speedup**.
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## What We Ask
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A patch is ready for review.
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1. Confirm receipt and assign a GitHub Security Advisory or issue reference (dotnet/efcore).
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2. Assess severity — efcore-0001 and efcore-0002 fire on every `SaveChanges()` call in applications with FK relationships.
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3. Coordinate a disclosure date — we are targeting 90 days from first contact.
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4. We will credit the EF Core team in the public disclosure. Preferred acknowledgment format welcome.
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Contact: see cover email. This brief is confidential until coordinated disclosure.
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