[analyzer] Detect use-after-free for field address (e.g., &ptr->field) (#152462)

This patch improves MallocChecker to detect use-after-free bugs when
a freed structure's field is passed by address (e.g., `&ptr->field`).

Previously, MallocChecker would miss such cases, as it only checked the
top-level symbol of argument values.
This patch analyzes the base region of arguments and extracts the
symbolic region (if any), allowing UAF detection even for field address
expressions.

Fixes #152446

clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp

@@ -3156,7 +3156,7 @@ void MallocChecker::checkPreCall(const CallEvent &Call,
   for (unsigned I = 0, E = Call.getNumArgs(); I != E; ++I) {
     SVal ArgSVal = Call.getArgSVal(I);
     if (isa<Loc>(ArgSVal)) {
-      SymbolRef Sym = ArgSVal.getAsSymbol();
+      SymbolRef Sym = ArgSVal.getAsSymbol(/*IncludeBaseRegions=*/true);
       if (!Sym)
         continue;
       if (checkUseAfterFree(Sym, C, Call.getArgExpr(I)))

clang/test/Analysis/malloc-checker-arg-uaf.c

@@ -0,0 +1,44 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=core,unix.Malloc -verify %s
+
+#include "Inputs/system-header-simulator-for-malloc.h"
+
+struct Obj {
+  int field;
+};
+
+void use(void *ptr);
+
+void test_direct_param_uaf() {
+  int *p = (int *)malloc(sizeof(int));
+  free(p);
+  use(p); // expected-warning{{Use of memory after it is released}}
+}
+
+void test_struct_field_uaf() {
+  struct Obj *o = (struct Obj *)malloc(sizeof(struct Obj));
+  free(o);
+  use(&o->field); // expected-warning{{Use of memory after it is released}}
+}
+
+void test_no_warning_const_int() {
+  use((void *)0x1234); // no-warning
+}
+
+void test_no_warning_stack() {
+  int x = 42;
+  use(&x); // no-warning
+}
+
+void test_nested_alloc() {
+  struct Obj *o = (struct Obj *)malloc(sizeof(struct Obj));
+  use(o);   // no-warning
+  free(o);
+  use(o);   // expected-warning{{Use of memory after it is released}}
+}
+
+void test_nested_field() {
+    struct Obj *o = (struct Obj *)malloc(sizeof(struct Obj));
+    int *f = &o->field;
+    free(o);
+    use(f); // expected-warning{{Use of memory after it is released}}
+}