[analyzer] StackAddrEscapeChecker: also check return for child stack frames (#126986)

Fixes #123459.

This changes checking of the returned expr to also look for memory
regions whose stack frame context was a child of the current stack frame
context, e.g., for cases like this given in #123459:

```
struct S { int *p; };
S f() {
  S s;
  {
    int a = 1;
    s.p = &a;
  }
  return s;
}
```

Author: ashfordium

clang/lib/StaticAnalyzer/Checkers/StackAddrEscapeChecker.cpp

@@ -274,7 +274,13 @@ class FindStackRegionsSymbolVisitor final : public SymbolVisitor {
   void SaveIfEscapes(const MemRegion *MR) {
     const StackSpaceRegion *SSR =
         MR->getMemorySpace()->getAs<StackSpaceRegion>();
-    if (SSR && SSR->getStackFrame() == PoppedStackFrame)
+
+    if (!SSR)
+      return;
+
+    const StackFrameContext *CapturedSFC = SSR->getStackFrame();
+    if (CapturedSFC == PoppedStackFrame ||
+        PoppedStackFrame->isParentOf(CapturedSFC))
       EscapingStackRegions.push_back(MR);
   }
 

clang/test/Analysis/stack-addr-ps.cpp

@@ -982,6 +982,51 @@ int& ret_local_field_ref() {
 }
 } //namespace return_address_of_true_positives
 
+namespace return_from_child_block_scope {
+struct S {
+  int *p;
+};
+
+S return_child_stack_context() {
+  S s;
+  {
+    int a = 1;
+    s = (S){ &a };
+  }
+  return s; // expected-warning {{Address of stack memory associated with local variable 'a' returned to caller}}
+}
+
+S return_child_stack_context_field() {
+  S s;
+  {
+    int a = 1;
+    s.p = &a;
+  }
+  return s; // expected-warning {{Address of stack memory associated with local variable 'a' returned to caller}}
+}
+
+// The below are reproducers from Issue #123459
+template <typename V>
+struct T {
+    V* q{};
+    T() = default;
+    T(T&& rhs) { q = rhs.q; rhs.q = nullptr;}
+    T& operator=(T&& rhs) { q = rhs.q; rhs.q = nullptr;}
+    void push_back(const V& v) { if (q == nullptr) q = new V(v); }
+    ~T() { delete q; }
+};
+
+T<S> f() {
+    T<S> t;
+    {
+        int a = 1;
+        t.push_back({ &a });
+    }
+    return t; // expected-warning {{Address of stack memory associated with local variable 'a' returned to caller}}
+}
+
+} // namespace return_from_child_block_scope
+
 namespace true_negatives_return_expressions {
 struct Container { int *x; };
 

clang/test/Analysis/stackaddrleak.c

@@ -68,3 +68,25 @@ int *g_no_lifetime_bound() {
   int i = 0;
   return f_no_lifetime_bound(&i); // no-warning
 }
+
+struct child_stack_context_s {
+  int *p;
+};
+
+struct child_stack_context_s return_child_stack_context() {
+  struct child_stack_context_s s;
+  {
+    int a = 1;
+    s = (struct child_stack_context_s){ &a };
+  }
+  return s; // expected-warning {{Address of stack memory associated with local variable 'a' returned to caller}}
+}
+
+struct child_stack_context_s return_child_stack_context_field() {
+  struct child_stack_context_s s;
+  {
+    int a = 1;
+    s.p = &a;
+  }
+  return s; // expected-warning {{Address of stack memory associated with local variable 'a' returned to caller}}
+}