Add a new path-sensitive checker for functions in <string.h>, for both null-terminated strings and memory blocks. Currently only checks memcpy(), memmove(), and bcopy(), but this is intended to be expanded soon.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@107722 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 358 insertions, 0 deletions

diff --git a/lib/Checker/CStringChecker.cpp b/lib/Checker/CStringChecker.cpp
new file mode 100644
index 0000000000..26e83dfa23
--- /dev/null
+++ b/lib/Checker/CStringChecker.cpp
@@ -0,0 +1,358 @@
+//= CStringChecker.h - Checks calls to C string functions ----------*- C++ -*-//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines CStringChecker, which is an assortment of checks on calls
+// to functions in <string.h>.
+//
+//===----------------------------------------------------------------------===//
+
+#include "GRExprEngineExperimentalChecks.h"
+#include "clang/Checker/BugReporter/BugType.h"
+#include "clang/Checker/PathSensitive/CheckerVisitor.h"
+#include "llvm/ADT/StringSwitch.h"
+
+using namespace clang;
+
+namespace {
+class CStringChecker : public CheckerVisitor<CStringChecker> {
+  BugType *BT_Bounds;
+  BugType *BT_Overlap;
+public:
+  CStringChecker()
+  : BT_Bounds(0), BT_Overlap(0) {}
+  static void *getTag() { static int tag; return &tag; }
+
+  bool EvalCallExpr(CheckerContext &C, const CallExpr *CE);
+
+  typedef const GRState *(CStringChecker::*FnCheck)(CheckerContext &,
+                                                    const CallExpr *);
+
+  const GRState *EvalMemcpy(CheckerContext &C, const CallExpr *CE);
+  const GRState *EvalMemmove(CheckerContext &C, const CallExpr *CE);
+  const GRState *EvalBcopy(CheckerContext &C, const CallExpr *CE);
+
+  // Utility methods
+  const GRState *CheckLocation(CheckerContext &C, const GRState *state,
+                               const Stmt *S, SVal l);
+  const GRState *CheckBufferAccess(CheckerContext &C, const GRState *state,
+                                   const Expr *Size,
+                                   const Expr *FirstBuf,
+                                   const Expr *SecondBuf = NULL);
+  const GRState *CheckOverlap(CheckerContext &C, const GRState *state,
+                              const Expr *First, const Expr *Second,
+                              const Expr *Size);
+  void EmitOverlapBug(CheckerContext &C, const GRState *state,
+                      const Stmt *First, const Stmt *Second);
+};
+} //end anonymous namespace
+
+void clang::RegisterCStringChecker(GRExprEngine &Eng) {
+  Eng.registerCheck(new CStringChecker());
+}
+
+// FIXME: This was originally copied from ArrayBoundChecker.cpp. Refactor?
+const GRState *CStringChecker::CheckLocation(CheckerContext &C,
+                                             const GRState *state,
+                                             const Stmt *S, SVal l) {
+  // Check for out of bound array element access.
+  const MemRegion *R = l.getAsRegion();
+  if (!R)
+    return state;
+
+  R = R->StripCasts();
+
+  const ElementRegion *ER = dyn_cast<ElementRegion>(R);
+  if (!ER)
+    return state;
+
+  assert(ER->getValueType(C.getASTContext()) == C.getASTContext().CharTy &&
+    "CheckLocation should only be called with char* ElementRegions");
+
+  // Get the size of the array.
+  const SubRegion *Super = cast<SubRegion>(ER->getSuperRegion());
+  ValueManager &ValMgr = C.getValueManager();
+  SVal Extent = ValMgr.convertToArrayIndex(Super->getExtent(ValMgr));
+  DefinedOrUnknownSVal Size = cast<DefinedOrUnknownSVal>(Extent);
+
+  // Get the index of the accessed element.
+  DefinedOrUnknownSVal &Idx = cast<DefinedOrUnknownSVal>(ER->getIndex());
+
+  const GRState *StInBound = state->AssumeInBound(Idx, Size, true);
+  const GRState *StOutBound = state->AssumeInBound(Idx, Size, false);
+  if (StOutBound && !StInBound) {
+    ExplodedNode *N = C.GenerateSink(StOutBound);
+    if (!N)
+      return NULL;
+
+    if (!BT_Bounds)
+      BT_Bounds = new BuiltinBug("Out-of-bound array access",
+        "Byte string function accesses out-of-bound array element "
+        "(buffer overflow)");
+
+    // FIXME: It would be nice to eventually make this diagnostic more clear,
+    // e.g., by referencing the original declaration or by saying *why* this
+    // reference is outside the range.
+
+    // Generate a report for this bug.
+    BuiltinBug *BT = static_cast<BuiltinBug*>(BT_Bounds);
+    RangedBugReport *report = new RangedBugReport(*BT, BT->getDescription(), N);
+
+    report->addRange(S->getSourceRange());
+    C.EmitReport(report);
+    return NULL;
+  }
+  
+  // Array bound check succeeded.  From this point forward the array bound
+  // should always succeed.
+  return StInBound;
+}
+
+const GRState *CStringChecker::CheckBufferAccess(CheckerContext &C,
+                                                 const GRState *state,
+                                                 const Expr *Size,
+                                                 const Expr *FirstBuf,
+                                                 const Expr *SecondBuf) {
+  ValueManager &VM = C.getValueManager();
+  SValuator &SV = VM.getSValuator();
+  ASTContext &Ctx = C.getASTContext();
+
+  QualType SizeTy = Ctx.getSizeType();
+  QualType PtrTy = Ctx.getPointerType(Ctx.CharTy);
+
+  // Get the access length and make sure it is known.
+  SVal LengthVal = state->getSVal(Size);
+  NonLoc *Length = dyn_cast<NonLoc>(&LengthVal);
+  if (!Length)
+    return state;
+
+  // Compute the offset of the last element to be accessed: size-1.
+  NonLoc One = cast<NonLoc>(VM.makeIntVal(1, SizeTy));
+  NonLoc LastOffset = cast<NonLoc>(SV.EvalBinOpNN(state, BinaryOperator::Sub,
+                                                  *Length, One, SizeTy));
+
+  // Check that the first buffer is sufficiently long.
+  SVal BufVal = state->getSVal(FirstBuf);
+  Loc BufStart = cast<Loc>(SV.EvalCast(BufVal, PtrTy, FirstBuf->getType()));
+  SVal BufEnd
+    = SV.EvalBinOpLN(state, BinaryOperator::Add, BufStart, LastOffset, PtrTy);
+  state = CheckLocation(C, state, FirstBuf, BufEnd);
+
+  // If the buffer isn't large enough, abort.
+  if (!state)
+    return NULL;
+
+  // If there's a second buffer, check it as well.
+  if (SecondBuf) {
+    BufVal = state->getSVal(SecondBuf);
+    BufStart = cast<Loc>(SV.EvalCast(BufVal, PtrTy, SecondBuf->getType()));
+    BufEnd
+      = SV.EvalBinOpLN(state, BinaryOperator::Add, BufStart, LastOffset, PtrTy);
+    state = CheckLocation(C, state, SecondBuf, BufEnd);
+  }
+
+  // Large enough or not, return this state!
+  return state;
+}
+
+const GRState *CStringChecker::CheckOverlap(CheckerContext &C,
+                                            const GRState *state,
+                                            const Expr *First,
+                                            const Expr *Second,
+                                            const Expr *Size) {
+  // Do a simple check for overlap: if the two arguments are from the same
+  // buffer, see if the end of the first is greater than the start of the second
+  // or vice versa.
+
+  ValueManager &VM = state->getStateManager().getValueManager();
+  SValuator &SV = VM.getSValuator();
+  ASTContext &Ctx = VM.getContext();
+  const GRState *stateTrue, *stateFalse;
+
+  // Get the buffer values and make sure they're known locations.
+  SVal FirstVal = state->getSVal(First);
+  SVal SecondVal = state->getSVal(Second);
+
+  Loc *FirstLoc = dyn_cast<Loc>(&FirstVal);
+  if (!FirstLoc)
+    return state;
+
+  Loc *SecondLoc = dyn_cast<Loc>(&SecondVal);
+  if (!SecondLoc)
+    return state;
+
+  // Are the two values the same?
+  DefinedOrUnknownSVal EqualTest = SV.EvalEQ(state, *FirstLoc, *SecondLoc);
+  llvm::tie(stateTrue, stateFalse) = state->Assume(EqualTest);
+
+  if (stateTrue && !stateFalse) {
+    // If the values are known to be equal, that's automatically an overlap.
+    EmitOverlapBug(C, stateTrue, First, Second);
+    return NULL;
+  }
+
+  // Assume the two expressions are not equal.
+  assert(stateFalse);
+  state = stateFalse;
+
+  // Which value comes first?
+  QualType CmpTy = Ctx.IntTy;
+  SVal Reverse = SV.EvalBinOpLL(state, BinaryOperator::GT,
+                                *FirstLoc, *SecondLoc, CmpTy);
+  DefinedOrUnknownSVal *ReverseTest = dyn_cast<DefinedOrUnknownSVal>(&Reverse);
+  if (!ReverseTest)
+    return state;
+
+  llvm::tie(stateTrue, stateFalse) = state->Assume(*ReverseTest);
+
+  if (stateTrue) {
+    if (stateFalse) {
+      // If we don't know which one comes first, we can't perform this test.
+      return state;
+    } else {
+      // Switch the values so that FirstVal is before SecondVal.
+      Loc *tmpLoc = FirstLoc;
+      FirstLoc = SecondLoc;
+      SecondLoc = tmpLoc;
+
+      // Switch the Exprs as well, so that they still correspond.
+      const Expr *tmpExpr = First;
+      First = Second;
+      Second = tmpExpr;
+    }
+  }
+
+  // Get the length, and make sure it too is known.
+  SVal LengthVal = state->getSVal(Size);
+  NonLoc *Length = dyn_cast<NonLoc>(&LengthVal);
+  if (!Length)
+    return state;
+
+  // Convert the first buffer's start address to char*.
+  // Bail out if the cast fails.
+  QualType CharPtrTy = Ctx.getPointerType(Ctx.CharTy);
+  SVal FirstStart = SV.EvalCast(*FirstLoc, CharPtrTy, First->getType());
+  Loc *FirstStartLoc = dyn_cast<Loc>(&FirstStart);
+  if (!FirstStartLoc)
+    return state;
+
+  // Compute the end of the first buffer. Bail out if THAT fails.
+  SVal FirstEnd = SV.EvalBinOpLN(state, BinaryOperator::Add,
+                                 *FirstStartLoc, *Length, CharPtrTy);
+  Loc *FirstEndLoc = dyn_cast<Loc>(&FirstEnd);
+  if (!FirstEndLoc)
+    return state;
+
+  // Is the end of the first buffer past the start of the second buffer?
+  SVal Overlap = SV.EvalBinOpLL(state, BinaryOperator::GT,
+                                *FirstEndLoc, *SecondLoc, CmpTy);
+  DefinedOrUnknownSVal *OverlapTest = dyn_cast<DefinedOrUnknownSVal>(&Overlap);
+  if (!OverlapTest)
+    return state;
+
+  llvm::tie(stateTrue, stateFalse) = state->Assume(*OverlapTest);
+
+  if (stateTrue && !stateFalse) {
+    // Overlap!
+    EmitOverlapBug(C, stateTrue, First, Second);
+    return NULL;
+  }
+
+  // Assume the two expressions don't overlap.
+  assert(stateFalse);
+  return stateFalse;
+}
+
+void CStringChecker::EmitOverlapBug(CheckerContext &C, const GRState *state,
+                                    const Stmt *First, const Stmt *Second) {
+  ExplodedNode *N = C.GenerateSink(state);
+  if (!N)
+    return;
+
+  if (!BT_Overlap)
+    BT_Overlap = new BugType("Unix API", "Improper arguments");
+
+  // Generate a report for this bug.
+  RangedBugReport *report = 
+    new RangedBugReport(*BT_Overlap,
+      "Arguments must not be overlapping buffers", N);
+  report->addRange(First->getSourceRange());
+  report->addRange(Second->getSourceRange());
+
+  C.EmitReport(report);
+}
+
+const GRState *
+CStringChecker::EvalMemcpy(CheckerContext &C, const CallExpr *CE) {
+  // void *memcpy(void *restrict dst, const void *restrict src, size_t n);
+  // memcpy() is like memmove(), but with the extra requirement that the buffers
+  // not overlap.
+  const GRState *state = EvalMemmove(C, CE);
+  if (!state)
+    return NULL;
+
+  return CheckOverlap(C, state, CE->getArg(0), CE->getArg(1), CE->getArg(2));
+}
+
+const GRState *
+CStringChecker::EvalMemmove(CheckerContext &C, const CallExpr *CE) {
+  // void *memmove(void *dst, const void *src, size_t n);
+  const Expr *Dest = CE->getArg(0);
+  const Expr *Source = CE->getArg(1);
+  const Expr *Size = CE->getArg(2);
+
+  // Check that the accesses will stay in bounds.
+  const GRState *state = C.getState();
+  state = CheckBufferAccess(C, state, Size, Dest, Source);
+  if (!state)
+    return NULL;
+
+  // The return value is the address of the destination buffer.
+  return state->BindExpr(CE, state->getSVal(Dest));
+}
+
+const GRState *
+CStringChecker::EvalBcopy(CheckerContext &C, const CallExpr *CE) {
+  // void bcopy(const void *src, void *dst, size_t n);
+  return CheckBufferAccess(C, C.getState(),
+                           CE->getArg(2), CE->getArg(0), CE->getArg(1));
+}
+
+bool CStringChecker::EvalCallExpr(CheckerContext &C, const CallExpr *CE) {
+  // Get the callee.  All the functions we care about are C functions
+  // with simple identifiers.
+  const GRState *state = C.getState();
+  const Expr *Callee = CE->getCallee();
+  const FunctionDecl *FD = state->getSVal(Callee).getAsFunctionDecl();
+
+  if (!FD)
+    return false;
+
+  // Get the name of the callee. If it's a builtin, strip off the prefix.
+  llvm::StringRef Name = FD->getName();
+  if (Name.startswith("__builtin_"))
+    Name = Name.substr(10);
+
+  FnCheck EvalFunction = llvm::StringSwitch<FnCheck>(Name)
+    .Case("memcpy", &CStringChecker::EvalMemcpy)
+    .Case("__memcpy_chk", &CStringChecker::EvalMemcpy)
+    .Case("memmove", &CStringChecker::EvalMemmove)
+    .Case("__memmove_chk", &CStringChecker::EvalMemmove)
+    .Case("bcopy", &CStringChecker::EvalBcopy)
+    .Default(NULL);
+
+  if (!EvalFunction)
+    // The callee isn't a string function. Let another checker handle it.
+    return false;
+
+  const GRState *NewState = (this->*EvalFunction)(C, CE);
+
+  if (NewState)
+    C.addTransition(NewState);
+  return true;
+}