path: root/lib/StaticAnalyzer/Checkers/GenericTaintChecker.cpp

//== GenericTaintChecker.cpp ----------------------------------- -*- C++ -*--=//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This checker defines the attack surface for generic taint propagation.
//
// The taint information produced by it might be useful to other checkers. For
// example, checkers should report errors which involve tainted data more
// aggressively, even if the involved symbols are under constrained.
//
//===----------------------------------------------------------------------===//
#include "ClangSACheckers.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include <climits>

using namespace clang;
using namespace ento;

namespace {
class GenericTaintChecker : public Checker< check::PostStmt<CallExpr>,
                                            check::PreStmt<CallExpr> > {
public:
  static const unsigned ReturnValueIndex = UINT_MAX;

private:
  mutable llvm::OwningPtr<BugType> BT;
  void initBugType() const;

  /// \brief Catch taint related bugs. Check if tainted data is passed to a
  /// system call etc.
  bool checkPre(const CallExpr *CE, CheckerContext &C) const;

  /// \brief Add taint sources on a pre-visit.
  void addSourcesPre(const CallExpr *CE, CheckerContext &C) const;

  /// \brief Propagate taint generated at pre-visit.
  bool propagateFromPre(const CallExpr *CE, CheckerContext &C) const;

  /// \brief Add taint sources on a post visit.
  void addSourcesPost(const CallExpr *CE, CheckerContext &C) const;

  /// \brief Given a pointer argument, get the symbol of the value it contains
  /// (points to).
  SymbolRef getPointedToSymbol(CheckerContext &C,
                               const Expr *Arg,
                               bool IssueWarning = false) const;

  /// Functions defining the attack surface.
  typedef const ProgramState *(GenericTaintChecker::*FnCheck)(const CallExpr *,
                                                       CheckerContext &C) const;
  const ProgramState *postScanf(const CallExpr *CE, CheckerContext &C) const;
  const ProgramState *postRetTaint(const CallExpr *CE, CheckerContext &C) const;

  /// Taint the scanned input if the file is tainted.
  const ProgramState *preFscanf(const CallExpr *CE, CheckerContext &C) const;
  /// Taint if any of the arguments are tainted.
  const ProgramState *preAnyArgs(const CallExpr *CE, CheckerContext &C) const;
  const ProgramState *preStrcpy(const CallExpr *CE, CheckerContext &C) const;

  /// Check if the region the expression evaluates to is the standard input,
  /// and thus, is tainted.
  bool isStdin(const Expr *E, CheckerContext &C) const;

  /// Check for CWE-134: Uncontrolled Format String.
  bool checkUncontrolledFormatString(const CallExpr *CE,
                                     CheckerContext &C) const;

public:
  static void *getTag() { static int Tag; return &Tag; }

  void checkPostStmt(const CallExpr *CE, CheckerContext &C) const;
  void checkPostStmt(const DeclRefExpr *DRE, CheckerContext &C) const;

  void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;

};
}

/// A set which is used to pass information from call pre-visit instruction
/// to the call post-visit. The values are unsigned integers, which are either
/// ReturnValueIndex, or indexes of the pointer/reference argument, which
/// points to data, which should be tainted on return.
namespace { struct TaintArgsOnPostVisit{}; }
namespace clang { namespace ento {
template<> struct ProgramStateTrait<TaintArgsOnPostVisit>
    :  public ProgramStatePartialTrait<llvm::ImmutableSet<unsigned> > {
  static void *GDMIndex() { return GenericTaintChecker::getTag(); }
};
}}

inline void GenericTaintChecker::initBugType() const {
  if (!BT)
    BT.reset(new BugType("Taint Analysis", "General"));
}

void GenericTaintChecker::checkPreStmt(const CallExpr *CE,
                                       CheckerContext &C) const {
  // Check for errors first.
  if (checkPre(CE, C))
    return;

  // Add taint second.
  addSourcesPre(CE, C);
}

void GenericTaintChecker::checkPostStmt(const CallExpr *CE,
                                        CheckerContext &C) const {
  if (propagateFromPre(CE, C))
    return;
  addSourcesPost(CE, C);
}

void GenericTaintChecker::addSourcesPre(const CallExpr *CE,
                                        CheckerContext &C) const {
  // Set the evaluation function by switching on the callee name.
  StringRef Name = C.getCalleeName(CE);
  if (Name.empty())
    return;
  FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name)
    .Case("atoi", &GenericTaintChecker::preAnyArgs)
    .Case("atol", &GenericTaintChecker::preAnyArgs)
    .Case("atoll", &GenericTaintChecker::preAnyArgs)
    .Case("fscanf", &GenericTaintChecker::preFscanf)
    .Cases("strcpy", "__builtin___strcpy_chk",
           "__inline_strcpy_chk", &GenericTaintChecker::preStrcpy)
    .Cases("stpcpy", "__builtin___stpcpy_chk", &GenericTaintChecker::preStrcpy)
    .Cases("strncpy", "__builtin___strncpy_chk", &GenericTaintChecker::preStrcpy)
    .Default(0);

  // Check and evaluate the call.
  const ProgramState *State = 0;
  if (evalFunction)
    State = (this->*evalFunction)(CE, C);
  if (!State)
    return;

  C.addTransition(State);
}

bool GenericTaintChecker::propagateFromPre(const CallExpr *CE,
                                           CheckerContext &C) const {
  const ProgramState *State = C.getState();

  // Depending on what was tainted at pre-visit, we determined a set of
  // arguments which should be tainted after the function returns. These are
  // stored in the state as TaintArgsOnPostVisit set.
  llvm::ImmutableSet<unsigned> TaintArgs = State->get<TaintArgsOnPostVisit>();
  for (llvm::ImmutableSet<unsigned>::iterator
         I = TaintArgs.begin(), E = TaintArgs.end(); I != E; ++I) {
    unsigned ArgNum  = *I;

    // Special handling for the tainted return value.
    if (ArgNum == ReturnValueIndex) {
      State = State->addTaint(CE, C.getLocationContext());
      continue;
    }

    // The arguments are pointer arguments. The data they are pointing at is
    // tainted after the call.
    const Expr* Arg = CE->getArg(ArgNum);
    SymbolRef Sym = getPointedToSymbol(C, Arg, true);
    if (Sym)
      State = State->addTaint(Sym);
  }

  // Clear up the taint info from the state.
  State = State->remove<TaintArgsOnPostVisit>();

  if (State != C.getState()) {
    C.addTransition(State);
    return true;
  }
  return false;
}

void GenericTaintChecker::addSourcesPost(const CallExpr *CE,
                                         CheckerContext &C) const {
  // Define the attack surface.
  // Set the evaluation function by switching on the callee name.
  StringRef Name = C.getCalleeName(CE);
  if (Name.empty())
    return;
  FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name)
    .Case("scanf", &GenericTaintChecker::postScanf)
    // TODO: Add support for vfscanf & family.
    .Case("getchar", &GenericTaintChecker::postRetTaint)
    .Case("getenv", &GenericTaintChecker::postRetTaint)
    .Case("fopen", &GenericTaintChecker::postRetTaint)
    .Case("fdopen", &GenericTaintChecker::postRetTaint)
    .Case("freopen", &GenericTaintChecker::postRetTaint)
    .Default(0);

  // If the callee isn't defined, it is not of security concern.
  // Check and evaluate the call.
  const ProgramState *State = 0;
  if (evalFunction)
    State = (this->*evalFunction)(CE, C);
  if (!State)
    return;

  C.addTransition(State);
}

bool GenericTaintChecker::checkPre(const CallExpr *CE, CheckerContext &C) const{

  if (checkUncontrolledFormatString(CE, C))
    return true;

  return false;
}

SymbolRef GenericTaintChecker::getPointedToSymbol(CheckerContext &C,
                                                  const Expr* Arg,