[-Wunsafe-buffer-usage] Add an unsafe gadget for pointer-arithmetic operations

[ziqingluo-90]

Summary

For -Wunsafe-buffer-usage diagnostics, we want to warn about pointer arithmetics since resulting pointers can be used to access buffers.
Therefore, I add an UnsafeGadget representing general pointer arithmetic operations.

[NoQ]

clang/lib/Analysis/UnsafeBufferUsage.cpp

319–320

Let's unhardcode the bind tags just like in the subscript patch?

[ziqingluo-90]

Did a rebase and addressed the comment.

[NoQ]

LGTM!

clang/lib/Analysis/UnsafeBufferUsage.cpp

354

It's pretty likely that it won't because we'll need a more specialized gadget for this.

clang/include/clang/Analysis/Analyses/UnsafeBufferUsageGadgets.def

 /// gadgets.
 #ifndef SAFE_GADGET
 #define SAFE_GADGET(name) GADGET(name)
 #endif
 
 UNSAFE_GADGET(Increment)
 UNSAFE_GADGET(Decrement)
 UNSAFE_GADGET(ArraySubscript)
+UNSAFE_GADGET(PointerArithmetic)
 
 #undef SAFE_GADGET
 #undef UNSAFE_GADGET
 #undef GADGET

clang/lib/Analysis/UnsafeBufferUsage.cpp

DeclUseList getClaimedVarUseSites() const override {
     if (const auto *DRE =
             dyn_cast<DeclRefExpr>(ASE->getBase()->IgnoreParenImpCasts())) {
       return {DRE};
     }
 
     return {};
   }
 };
+
+/// A pointer arithmetic expression of one of the forms:
+///  \code
+///  ptr + n | n + ptr | ptr - n | ptr += n | ptr -= n
+///  \endcode
+class PointerArithmeticGadget : public UnsafeGadget {
+  static constexpr const char *const PointerArithmeticTag = "ptrAdd";
+  static constexpr const char *const PointerArithmeticPointerTag = "ptrAddPtr";
+  const BinaryOperator *PA; // pointer arithmetic expression
+  const Expr * Ptr;         // the pointer expression in `PA`
+
+public:
+    PointerArithmeticGadget(const MatchFinder::MatchResult &Result)
+      : UnsafeGadget(Kind::PointerArithmetic),
+        PA(Result.Nodes.getNodeAs<BinaryOperator>(PointerArithmeticTag)),
+        Ptr(Result.Nodes.getNodeAs<Expr>(PointerArithmeticPointerTag)) {}
+
+  static bool classof(const Gadget *G) {
+    return G->getKind() == Kind::PointerArithmetic;
+  }
+
+  static Matcher matcher() {
+    auto HasIntegerType = anyOf(
+          hasType(isInteger()), hasType(enumType()));
+    auto PtrAtRight = allOf(hasOperatorName("+"),
+                            hasRHS(expr(hasPointerType()).bind(PointerArithmeticPointerTag)),
+                            hasLHS(HasIntegerType));
+    auto PtrAtLeft = allOf(
+           anyOf(hasOperatorName("+"), hasOperatorName("-"),
+                 hasOperatorName("+="), hasOperatorName("-=")),
+           hasLHS(expr(hasPointerType()).bind(PointerArithmeticPointerTag)),
+           hasRHS(HasIntegerType));
+
+    return stmt(binaryOperator(anyOf(PtrAtLeft, PtrAtRight)).bind(PointerArithmeticTag));
+  }
+
+  const Stmt *getBaseStmt() const override { return PA; }
+
+  DeclUseList getClaimedVarUseSites() const override {
+    if (const auto *DRE =
+            dyn_cast<DeclRefExpr>(Ptr->IgnoreParenImpCasts())) {
+      return {DRE};
+    }
+
+    return {};
+  }
+  // FIXME: pointer adding zero should be fine
+  //FIXME: this gadge will need a fix-it
+};
 } // namespace
 
 namespace {
 // An auxiliary tracking facility for the fixit analysis. It helps connect
 // declarations to its and make sure we've covered all uses with our analysis
 // before we try to fix the declaration.
 class DeclUseTracker {
   using UseSetTy = SmallSet<const DeclRefExpr *, 16>;

clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp

 
 template<typename T, int N> T f(T t, T * pt, T a[N], T (&b)[N]) {
   foo(pt[1],    // expected-warning{{unchecked operation on raw buffer in expression}}
       a[1],     // expected-warning{{unchecked operation on raw buffer in expression}}
       b[1]);    // `b` is of array type
   return &t[1]; // expected-warning{{unchecked operation on raw buffer in expression}}
 }
 
+// Testing pointer arithmetic for pointer-to-int, qualified multi-level
+// pointer, pointer to a template type, and auto type
+T_ptr_t getPtr();
+
+template<typename T>
+void testPointerArithmetic(int * p, const int **q, T * x) {
+  int a[10];
+  auto y = &a[0];
+
+  foo(p + 1, 1 + p, p - 1,      // expected-warning3{{unchecked operation on raw buffer in expression}}
+      *q + 1, 1 + *q, *q - 1,   // expected-warning3{{unchecked operation on raw buffer in expression}}
+      x + 1, 1 + x, x - 1,      // expected-warning3{{unchecked operation on raw buffer in expression}}
+      y + 1, 1 + y, y - 1,      // expected-warning3{{unchecked operation on raw buffer in expression}}
+      getPtr() + 1, 1 + getPtr(), getPtr() - 1 // expected-warning3{{unchecked operation on raw buffer in expression}}
+      );
+
+  p += 1;  p -= 1;  // expected-warning2{{unchecked operation on raw buffer in expression}}
+  *q += 1; *q -= 1; // expected-warning2{{unchecked operation on raw buffer in expression}}
+  y += 1; y -= 1;   // expected-warning2{{unchecked operation on raw buffer in expression}}
+  x += 1; x -= 1;   // expected-warning2{{unchecked operation on raw buffer in expression}}
+}
+
 void testTemplate(int * p) {
   int *a[10];
   foo(f(p, &p, a, a)[1]); // expected-warning{{unchecked operation on raw buffer in expression}}, \
                              expected-note{{in instantiation of function template specialization 'f<int *, 10>' requested here}}
+
+  const int **q = const_cast<const int **>(&p);
+
+  testPointerArithmetic(p, q, p); //expected-note{{in instantiation of function template specialization 'testPointerArithmetic<int>' requested here}}
 }
 
 void testPointerToMember() {
   struct S_t {
     int x;
     int * y;
   } S;