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
21using namespace clang;
22using namespace ento;
23
24namespace {
25class 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
34public:
35  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
36};
37
38bool 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
67void 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
101void ento::registerStringChecker(CheckerManager &Mgr) {
102  Mgr.registerChecker<StringChecker>();
103}
104
105bool ento::shouldRegisterStringChecker(const CheckerManager &) { return true; }
106