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refactor(inboundapi): M3.4 ForbiddenApiChecker delegates to shared ScriptAnalysis validator

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This commit is contained in:
Joseph Doherty
2026-06-16 19:35:43 -04:00
parent 069c0e0b1a
commit 784fee7b07
3 changed files with 70 additions and 187 deletions
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src/ZB.MOM.WW.ScadaBridge.InboundAPI/ForbiddenApiChecker.cs
+17 -183
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@@ -1,6 +1,4 @@
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using ZB.MOM.WW.ScadaBridge.ScriptAnalysis;
namespace ZB.MOM.WW.ScadaBridge.InboundAPI;
@@ -8,89 +6,30 @@ namespace ZB.MOM.WW.ScadaBridge.InboundAPI;
/// InboundAPI-005: Enforces the ScadaBridge script trust model on inbound API method
/// scripts before they are compiled into executable handlers.
///
/// The trust model (CLAUDE.md, Akka.NET conventions) forbids scripts from reaching
/// <c>System.IO</c>, <c>System.Diagnostics.Process</c>, <c>System.Threading</c>,
/// <c>System.Reflection</c>, and raw network APIs. Roslyn scripting performs no
/// API allow/deny-listing — restricting default imports is a convenience, not a
/// sandbox — so a script can fully-qualify any referenced type. This static check
/// walks the script syntax tree and rejects any reference to a forbidden namespace,
/// whether reached through a <c>using</c> directive or a fully-qualified name.
/// This class is now a thin shim that delegates to the shared, authoritative
/// <see cref="ScriptTrustValidator.FindViolations"/> implemented in
/// <c>ZB.MOM.WW.ScadaBridge.ScriptAnalysis</c> (M3.4). The unified validator runs
/// both a semantic symbol pass (catching alias / <c>global::</c> / <c>using static</c>
/// escapes) and the reflection-gateway + <c>dynamic</c> / <c>Activator</c> syntactic
/// hardening that previously lived exclusively in this file.
///
/// <para>
/// InboundAPI-015: a purely namespace-textual deny-list is bypassable because
/// reflection is reachable through members of <em>permitted</em> types that never
/// spell a forbidden namespace, e.g.
/// <c>typeof(string).Assembly.GetType("System.IO.File")</c>. The walker therefore
/// also rejects a curated set of reflection-gateway member names (<c>GetType</c>,
/// <c>Assembly</c>, <c>GetMethod</c>, <c>InvokeMember</c>, <c>CreateInstance</c>, …)
/// and the <c>dynamic</c> keyword. This is hardening of a best-effort static check,
/// <strong>not</strong> a true sandbox — a determined script author may still find
/// a vector the syntax walker cannot see (see the security notes in
/// <c>code-reviews/InboundAPI/findings.md</c>, InboundAPI-015). The check is
/// defence-in-depth; genuine containment needs a runtime boundary (restricted
/// <c>AssemblyLoadContext</c> / curated reference set / out-of-process sandbox).
/// <c>typeof(string).Assembly.GetType("System.IO.File")</c>. The shared validator
/// handles this with both semantic resolution and reflection-gateway member
/// hardening — <c>GetType</c>, <c>Assembly</c>, <c>GetMethod</c>, <c>InvokeMember</c>,
/// <c>CreateInstance</c>, and the <c>dynamic</c> keyword are all rejected. This
/// remains hardening of a best-effort static check, <strong>not</strong> a true sandbox
/// (see the security notes in <c>code-reviews/InboundAPI/findings.md</c>,
/// InboundAPI-015). The check is defence-in-depth; genuine containment needs a
/// runtime boundary (restricted <c>AssemblyLoadContext</c> / curated reference set /
/// out-of-process sandbox).
/// </para>
/// </summary>
public static class ForbiddenApiChecker
{
/// <summary>
/// Namespace prefixes the trust model forbids. A script segment matches if it is
/// equal to one of these or is a child namespace of it.
/// </summary>
private static readonly string[] ForbiddenNamespaces =
{
"System.IO",
"System.Diagnostics", // covers Process
"System.Threading", // Task/Tasks is explicitly re-allowed below
"System.Reflection",
"System.Net", // raw network (Sockets, HttpClient, etc.)
"System.Runtime.InteropServices",
"Microsoft.Win32",
};
/// <summary>
/// Namespaces that would otherwise be caught by a forbidden prefix but are
/// required for normal async script authoring and carry no host-access risk.
/// </summary>
private static readonly string[] AllowedExceptions =
{
"System.Threading.Tasks",
};
/// <summary>
/// InboundAPI-015: member names that are reflection gateways. Reaching any of
/// these — even off a permitted type such as <c>typeof(string)</c> or a plain
/// <c>string</c> — lets a script escape the namespace deny-list (obtain an
/// arbitrary <c>Type</c>, load an assembly, late-bind a method). They are
/// rejected regardless of the receiver expression. <c>Invoke</c> is deliberately
/// excluded because <c>Action</c>/<c>Func</c> delegate invocation is legitimate;
/// the reflection <c>MethodInfo.Invoke</c> path is already cut off by rejecting
/// the <c>GetMethod</c>/<c>GetConstructor</c> that produces the <c>MethodInfo</c>.
/// </summary>
private static readonly HashSet<string> ForbiddenMemberNames = new(StringComparer.Ordinal)
{
"GetType", // object.GetType() / Type.GetType(string) — yields a System.Type
"GetTypeInfo", // -> TypeInfo (reflection)
"Assembly", // Type.Assembly — yields a System.Reflection.Assembly
"Module", // Type.Module / MethodBase.Module
"CreateInstance", // Activator.CreateInstance / Assembly.CreateInstance
"InvokeMember", // Type.InvokeMember — late-bound dispatch
"GetMethod",
"GetMethods",
"GetConstructor",
"GetConstructors",
"GetField",
"GetFields",
"GetProperty",
"GetProperties",
"GetMember",
"GetMembers",
"GetRuntimeMethod",
"GetRuntimeMethods",
"MethodHandle", // RuntimeMethodHandle escape
"TypeHandle",
};
/// <summary>
/// Analyses the script source and returns the list of trust-model violations.
/// An empty list means the script is acceptable.
@@ -102,111 +41,6 @@ public static class ForbiddenApiChecker
if (string.IsNullOrWhiteSpace(scriptCode))
return Array.Empty<string>();
var tree = CSharpSyntaxTree.ParseText(
scriptCode,
new CSharpParseOptions(kind: SourceCodeKind.Script));
var walker = new ForbiddenApiWalker();
walker.Visit(tree.GetRoot());
return walker.Violations;
}
private static bool IsForbidden(string dottedName)
{
foreach (var allowed in AllowedExceptions)
{
if (dottedName == allowed || dottedName.StartsWith(allowed + ".", StringComparison.Ordinal))
return false;
}
foreach (var forbidden in ForbiddenNamespaces)
{
if (dottedName == forbidden || dottedName.StartsWith(forbidden + ".", StringComparison.Ordinal))
return true;
}
return false;
}
private sealed class ForbiddenApiWalker : CSharpSyntaxWalker
{
private readonly List<string> _violations = new();
/// <summary>Gets the accumulated list of trust-model violation descriptions.</summary>
public IReadOnlyList<string> Violations => _violations;
/// <inheritdoc />
public override void VisitUsingDirective(UsingDirectiveSyntax node)
{
if (node.Name is not null && IsForbidden(node.Name.ToString()))
_violations.Add($"forbidden namespace import '{node.Name}'");
base.VisitUsingDirective(node);
}
/// <inheritdoc />
public override void VisitQualifiedName(QualifiedNameSyntax node)
{
// Check the longest qualified name; do not descend so a single
// System.IO.File reference is reported once, not three times.
var text = node.ToString();
if (IsForbidden(text))
{
_violations.Add($"forbidden type reference '{text}'");
return;
}
base.VisitQualifiedName(node);
}
/// <inheritdoc />
public override void VisitMemberAccessExpression(MemberAccessExpressionSyntax node)
{
// Catches fully-qualified expressions such as System.IO.File.Delete(...).
var text = node.ToString();
if (IsForbidden(text))
{
_violations.Add($"forbidden API access '{text}'");
return;
}
// InboundAPI-015: reject reflection-gateway members regardless of the
// receiver. typeof(string).Assembly.GetType("System.IO.File") never
// spells a forbidden namespace, but '.Assembly' and '.GetType' do
// appear here as the accessed member name.
var memberName = node.Name.Identifier.ValueText;
if (ForbiddenMemberNames.Contains(memberName))
{
_violations.Add($"forbidden reflection member access '.{memberName}'");
// Still descend: the receiver may contain a further violation.
}
base.VisitMemberAccessExpression(node);
}
/// <inheritdoc />
public override void VisitIdentifierName(IdentifierNameSyntax node)
{
// InboundAPI-015: 'dynamic' widens late-bound member access that the
// static walker cannot see through — reject its use outright. The
// 'dynamic' contextual keyword surfaces as an identifier name.
if (node.Identifier.ValueText == "dynamic")
{
_violations.Add("forbidden use of the 'dynamic' keyword");
return;
}
// InboundAPI-015: a bare reference to the reflection entry-point types
// (e.g. 'Activator', 'Type') as an identifier. 'Activator' has no
// non-reflection use; flag it. ('Type' as an identifier is too broad
// to flag here — the gateway members above already cut off its use.)
if (node.Identifier.ValueText == "Activator")
{
_violations.Add("forbidden reflection type reference 'Activator'");
return;
}
base.VisitIdentifierName(node);
}
return ScriptTrustValidator.FindViolations(scriptCode);
}
}
src/ZB.MOM.WW.ScadaBridge.InboundAPI/ZB.MOM.WW.ScadaBridge.InboundAPI.csproj
+1
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@@ -17,6 +17,7 @@
<!-- AuditWriteMiddleware reads AuditLogOptions.InboundMaxBytes to bound
per-request request/response audit capture at the source. -->
<ProjectReference Include="../ZB.MOM.WW.ScadaBridge.AuditLog/ZB.MOM.WW.ScadaBridge.AuditLog.csproj" />
<ProjectReference Include="../ZB.MOM.WW.ScadaBridge.ScriptAnalysis/ZB.MOM.WW.ScadaBridge.ScriptAnalysis.csproj" />
</ItemGroup>
<ItemGroup>