clang/lib/StaticAnalyzer/Checkers/StringChecker.cpp

   1 //=== StringChecker.cpp -------------------------------------------*- C++ -*--//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements the modeling of the std::basic_string type.
  10 // This involves checking preconditions of the operations and applying the
  11 // effects of the operations, e.g. their post-conditions.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
  16 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
  17 #include "clang/StaticAnalyzer/Core/PathSensitive/CallDescription.h"
  18 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
  19 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
  20
  21 using namespace clang;
  22 using namespace ento;
  23
  24 namespace {
  25 class StringChecker : public Checker<check::PreCall> {
  26   BugType BT_Null{this, "Dereference of null pointer", categories::LogicError};
  27   mutable const FunctionDecl *StringConstCharPtrCtor = nullptr;
  28   mutable CanQualType SizeTypeTy;
  29   const CallDescription TwoParamStdStringCtor = {
  30       {"std", "basic_string", "basic_string"}, 2, 2};
  31
  32   bool isCharToStringCtor(const CallEvent &Call, const ASTContext &ACtx) const;
  33
  34 public:
  35   void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
  36 };
  37
  38 bool StringChecker::isCharToStringCtor(const CallEvent &Call,
  39                                        const ASTContext &ACtx) const {
  40   if (!TwoParamStdStringCtor.matches(Call))
  41     return false;
  42   const auto *FD = dyn_cast<FunctionDecl>(Call.getDecl());
  43   assert(FD);
  44
  45   // See if we already cached it.
  46   if (StringConstCharPtrCtor && StringConstCharPtrCtor == FD)
  47     return true;
  48
  49   // Verify that the parameters have the expected types:
  50   // - arg 1: `const CharT *`
  51   // - arg 2: some allocator - which is definately not `size_t`.
  52   const QualType Arg1Ty = Call.getArgExpr(0)->getType().getCanonicalType();
  53   const QualType Arg2Ty = Call.getArgExpr(1)->getType().getCanonicalType();
  54
  55   if (!Arg1Ty->isPointerType())
  56     return false;
  57
  58   // It makes sure that we don't select the `string(const char* p, size_t len)`
  59   // overload accidentally.
  60   if (Arg2Ty.getCanonicalType() == ACtx.getSizeType())
  61     return false;
  62
  63   StringConstCharPtrCtor = FD; // Cache the decl of the right overload.
  64   return true;
  65 }
  66
  67 void StringChecker::checkPreCall(const CallEvent &Call,
  68                                  CheckerContext &C) const {
  69   if (!isCharToStringCtor(Call, C.getASTContext()))
  70     return;
  71   const auto Param = Call.getArgSVal(0).getAs<Loc>();
  72   if (!Param)
  73     return;
  74
  75   // We managed to constrain the parameter to non-null.
  76   ProgramStateRef NotNull, Null;
  77   std::tie(NotNull, Null) = C.getState()->assume(*Param);
  78
  79   if (NotNull) {
  80     const auto Callback = [Param](PathSensitiveBugReport &BR) -> std::string {
  81       return BR.isInteresting(*Param) ? "Assuming the pointer is not null."
  82                                       : "";
  83     };
  84
  85     // Emit note only if this operation constrained the pointer to be null.
  86     C.addTransition(NotNull, Null ? C.getNoteTag(Callback) : nullptr);
  87     return;
  88   }
  89
  90   // We found a path on which the parameter is NULL.
  91   if (ExplodedNode *N = C.generateErrorNode(C.getState())) {
  92     auto R = std::make_unique<PathSensitiveBugReport>(
  93         BT_Null, "The parameter must not be null", N);
  94     bugreporter::trackExpressionValue(N, Call.getArgExpr(0), *R);
  95     C.emitReport(std::move(R));
  96   }
  97 }
  98
  99 } // end anonymous namespace
 100
 101 void ento::registerStringChecker(CheckerManager &Mgr) {
 102   Mgr.registerChecker<StringChecker>();
 103 }
 104
 105 bool ento::shouldRegisterStringChecker(const CheckerManager &) { return true; }