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//== 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/BugReporter/BugType.h"
using namespace clang;
using namespace ento;
namespace {
class GenericTaintChecker : public Checker< check::PostStmt<CallExpr>,
check::PostStmt<DeclRefExpr> > {
mutable llvm::OwningPtr<BugType> BT;
void initBugType() const;
/// Given a pointer argument, get the symbol of the value it contains
/// (points to).
SymbolRef getPointedToSymbol(CheckerContext &C,
const Expr* Arg,
bool IssueWarning = true) const;
/// Functions defining the attacke surface.
typedef void (GenericTaintChecker::*FnCheck)(const CallExpr *,
CheckerContext &C) const;
void processScanf(const CallExpr *CE, CheckerContext &C) const;
void processFscanf(const CallExpr *CE, CheckerContext &C) const;
void processRetTaint(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;
public:
void checkPostStmt(const CallExpr *CE, CheckerContext &C) const;
void checkPostStmt(const DeclRefExpr *DRE, CheckerContext &C) const;
};
}
inline void GenericTaintChecker::initBugType() const {
if (!BT)
BT.reset(new BugType("Tainted data checking", "General"));
}
void GenericTaintChecker::checkPostStmt(const CallExpr *CE,
CheckerContext &C) const {
if (!C.getState())
return;
StringRef Name = C.getCalleeName(CE);
// Define the attack surface.
// Set the evaluation function by switching on the callee name.
FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name)
.Case("scanf", &GenericTaintChecker::processScanf)
.Case("fscanf", &GenericTaintChecker::processFscanf)
.Case("sscanf", &GenericTaintChecker::processFscanf)
// TODO: Add support for vfscanf & family.
.Case("getchar", &GenericTaintChecker::processRetTaint)
.Case("getenv", &GenericTaintChecker::processRetTaint)
.Case("fopen", &GenericTaintChecker::processRetTaint)
.Case("fdopen", &GenericTaintChecker::processRetTaint)
.Case("freopen", &GenericTaintChecker::processRetTaint)
.Default(NULL);
// If the callee isn't defined, it is not of security concern.
// Check and evaluate the call.
if (evalFunction)
(this->*evalFunction)(CE, C);
}
void GenericTaintChecker::checkPostStmt(const DeclRefExpr *DRE,
CheckerContext &C) const {
if (isStdin(DRE, C)) {
const ProgramState *NewState = C.getState()->addTaint(DRE);
C.addTransition(NewState);
}
}
SymbolRef GenericTaintChecker::getPointedToSymbol(CheckerContext &C,
const Expr* Arg,
bool IssueWarning) const {
const ProgramState *State = C.getState();
SVal AddrVal = State->getSVal(Arg->IgnoreParens());
if (AddrVal.isUnknownOrUndef())
return 0;
Loc *AddrLoc = dyn_cast<Loc>(&AddrVal);
if (!AddrLoc && !IssueWarning)
return 0;
// If the Expr is not a location, issue a warning.
if (!AddrLoc) {
assert(IssueWarning);
if (ExplodedNode *N = C.generateSink(State)) {
initBugType();
BugReport *report = new BugReport(*BT, "Pointer argument is expected.",N);
report->addRange(Arg->getSourceRange());
C.EmitReport(report);
}
return 0;
}
SVal Val = State->getSVal(*AddrLoc);
return Val.getAsSymbol();
}
void GenericTaintChecker::processScanf(const CallExpr *CE,
CheckerContext &C) const {
const ProgramState *State = C.getState();
assert(CE->getNumArgs() >= 2);
SVal x = State->getSVal(CE->getArg(1));
// All arguments except for the very first one should get taint.
for (unsigned int i = 1; i < CE->getNumArgs(); ++i) {
// The arguments are pointer arguments. The data they are pointing at is
// tainted after the call.
const Expr* Arg = CE->getArg(i);
SymbolRef Sym = getPointedToSymbol(C, Arg);
if (Sym)
State = State->addTaint(Sym);
}
C.addTransition(State);
}
/// If argument 0 (file descriptor) is tainted, all arguments except for arg 0
/// and arg 1 should get taint.
void GenericTaintChecker::processFscanf(const CallExpr *CE,
CheckerContext &C) const {
const ProgramState *State = C.getState();
assert(CE->getNumArgs() >= 2);
// Check is the file descriptor is tainted.
if (!State->isTainted(CE->getArg(0)) && !isStdin(CE->getArg(0), C))
return;
// All arguments except for the first two should get taint.
for (unsigned int i = 2; i < CE->getNumArgs(); ++i) {
// The arguments are pointer arguments. The data they are pointing at is
// tainted after the call.
const Expr* Arg = CE->getArg(i);
SymbolRef Sym = getPointedToSymbol(C, Arg);
if (Sym)
State = State->addTaint(Sym);
}
C.addTransition(State);
}
void GenericTaintChecker::processRetTaint(const CallExpr *CE,
CheckerContext &C) const {
const ProgramState *NewState = C.getState()->addTaint(CE);
C.addTransition(NewState);
}
bool GenericTaintChecker::isStdin(const Expr *E,
CheckerContext &C) const {
const ProgramState *State = C.getState();
SVal Val = State->getSVal(E);
// stdin is a pointer, so it would be a region.
const MemRegion *MemReg = Val.getAsRegion();
// The region should be symbolic, we do not know it's value.
const SymbolicRegion *SymReg = dyn_cast_or_null<SymbolicRegion>(MemReg);
if (!SymReg)
return false;
// Get it's symbol and find the declaration region it's pointing to.
const SymbolRegionValue *Sm =dyn_cast<SymbolRegionValue>(SymReg->getSymbol());
if (!Sm)
return false;
const DeclRegion *DeclReg = dyn_cast_or_null<DeclRegion>(Sm->getRegion());
if (!DeclReg)
return false;
// This region corresponds to a declaration, find out if it's a global/extern
// variable named stdin with the proper type.
if (const VarDecl *D = dyn_cast_or_null<VarDecl>(DeclReg->getDecl())) {
D = D->getCanonicalDecl();
if ((D->getName().find("stdin") != StringRef::npos) && D->isExternC())
if (const PointerType * PtrTy =
dyn_cast<PointerType>(D->getType().getTypePtr()))
if (PtrTy->getPointeeType() == C.getASTContext().getFILEType())
return true;
}
return false;
}
void ento::registerGenericTaintChecker(CheckerManager &mgr) {
mgr.registerChecker<GenericTaintChecker>();
}
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