Merge pull request #9617 from 9999years/stack-overflow-segfault

Fix segfault on infinite recursion in some cases

(cherry picked from commit bf1b294bd81ca76c5ec9fe3ecd52196bf52a8300)
Change-Id: Id137541426ec8536567835953fccf986a3aebf16

src/libexpr/eval-settings.hh

@@ -111,6 +111,9 @@ struct EvalSettings : Config
 
     Setting<bool> traceVerbose{this, false, "trace-verbose",
         "Whether `builtins.traceVerbose` should trace its first argument when evaluated."};
+
+    Setting<unsigned int> maxCallDepth{this, 10000, "max-call-depth",
+        "The maximum function call depth to allow before erroring."};
 };
 
 extern EvalSettings evalSettings;

src/libexpr/eval.cc

@@ -1525,9 +1525,27 @@ void ExprLambda::eval(EvalState & state, Env & env, Value & v)
     v.mkLambda(&env, this);
 }
 
+namespace {
+/** Increments a count on construction and decrements on destruction.
+ */
+class CallDepth {
+  size_t & count;
+public:
+  CallDepth(size_t & count) : count(count) {
+    ++count;
+  }
+  ~CallDepth() {
+    --count;
+  }
+};
+};
 
 void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const PosIdx pos)
 {
+    if (callDepth > evalSettings.maxCallDepth)
+        error("stack overflow; max-call-depth exceeded").atPos(pos).template debugThrow<EvalError>();
+    CallDepth _level(callDepth);
+
     auto trace = evalSettings.traceFunctionCalls
         ? std::make_unique<FunctionCallTrace>(positions[pos])
         : nullptr;

src/libexpr/eval.hh

@@ -629,6 +629,11 @@ private:
         const SourcePath & basePath,
         std::shared_ptr<StaticEnv> & staticEnv);
 
+    /**
+     * Current Nix call stack depth, used with `max-call-depth` setting to throw stack overflow hopefully before we run out of system stack.
+     */
+    size_t callDepth = 0;
+
 public:
 
     /**