[analyzer] CStringChecker: Fix a crash on C++ overloads of standard f…

…unctions.

It turns out that it's not all that uncommon to have a C++ override of, say,
memcpy that receives a structure (or two) by reference (or by value, if it's
being copied from) and copies memory from it (or into it, if it's passed
by reference). In this case the argument will be of structure type (recall that
expressions of reference type do not exist: instead, C++ classifies expressions
into prvalues and lvalues and xvalues).

In this scenario we crash because we are trying to assume that, say,
a memory region is equal to an empty CompoundValue (the non-lazy one; this is
what makeZeroVal() return for compound types and it represents prvalue of
an object that is initialized with an empty initializer list).

Add defensive checks.

Differential Revision: https://reviews.llvm.org/D55873

rdar://problem/45366551

llvm-svn: 349682

clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp

@@ -188,7 +188,7 @@ class CStringChecker : public Checker< eval::Call,
                                         const Expr *Buf,
                                         const char *message = nullptr,
                                         bool WarnAboutSize = false) const {
-    // This is a convenience override.
+    // This is a convenience overload.
     return CheckBufferAccess(C, state, Size, Buf, nullptr, message, nullptr,
                              WarnAboutSize);
   }
@@ -2254,64 +2254,86 @@ static bool isCPPStdLibraryFunction(const FunctionDecl *FD, StringRef Name) {
 // The driver method, and other Checker callbacks.
 //===----------------------------------------------------------------------===//
 
-bool CStringChecker::evalCall(const CallExpr *CE, CheckerContext &C) const {
+static CStringChecker::FnCheck identifyCall(const CallExpr *CE,
+                                            CheckerContext &C) {
   const FunctionDecl *FDecl = C.getCalleeDecl(CE);
-
   if (!FDecl)
-    return false;
+    return nullptr;
+
+  // Pro-actively check that argument types are safe to do arithmetic upon.
+  // We do not want to crash if someone accidentally passes a structure
+  // into, say, a C++ overload of any of these functions.
+  if (isCPPStdLibraryFunction(FDecl, "copy")) {
+    if (CE->getNumArgs() < 3 || !CE->getArg(2)->getType()->isPointerType())
+      return nullptr;
+    return &CStringChecker::evalStdCopy;
+  } else if (isCPPStdLibraryFunction(FDecl, "copy_backward")) {
+    if (CE->getNumArgs() < 3 || !CE->getArg(2)->getType()->isPointerType())
+      return nullptr;
+    return &CStringChecker::evalStdCopyBackward;
+  } else {
+    // An umbrella check for all C library functions.
+    for (auto I: CE->arguments()) {
+      QualType T = I->getType();
+      if (!T->isIntegralOrEnumerationType() && !T->isPointerType())
+        return nullptr;
+    }
+  }
 
   // FIXME: Poorly-factored string switches are slow.
-  FnCheck evalFunction = nullptr;
   if (C.isCLibraryFunction(FDecl, "memcpy"))
-    evalFunction =  &CStringChecker::evalMemcpy;
+    return &CStringChecker::evalMemcpy;
   else if (C.isCLibraryFunction(FDecl, "mempcpy"))
-    evalFunction =  &CStringChecker::evalMempcpy;
+    return &CStringChecker::evalMempcpy;
   else if (C.isCLibraryFunction(FDecl, "memcmp"))
-    evalFunction =  &CStringChecker::evalMemcmp;
+    return &CStringChecker::evalMemcmp;
   else if (C.isCLibraryFunction(FDecl, "memmove"))
-    evalFunction =  &CStringChecker::evalMemmove;
-  else if (C.isCLibraryFunction(FDecl, "memset") || 
-    C.isCLibraryFunction(FDecl, "explicit_memset"))
-    evalFunction =  &CStringChecker::evalMemset;
+    return &CStringChecker::evalMemmove;
+  else if (C.isCLibraryFunction(FDecl, "memset") ||
+           C.isCLibraryFunction(FDecl, "explicit_memset"))
+    return &CStringChecker::evalMemset;
   else if (C.isCLibraryFunction(FDecl, "strcpy"))
-    evalFunction =  &CStringChecker::evalStrcpy;
+    return &CStringChecker::evalStrcpy;
   else if (C.isCLibraryFunction(FDecl, "strncpy"))
-    evalFunction =  &CStringChecker::evalStrncpy;
+    return &CStringChecker::evalStrncpy;
   else if (C.isCLibraryFunction(FDecl, "stpcpy"))
-    evalFunction =  &CStringChecker::evalStpcpy;
+    return &CStringChecker::evalStpcpy;
   else if (C.isCLibraryFunction(FDecl, "strlcpy"))
-    evalFunction =  &CStringChecker::evalStrlcpy;
+    return &CStringChecker::evalStrlcpy;
   else if (C.isCLibraryFunction(FDecl, "strcat"))
-    evalFunction =  &CStringChecker::evalStrcat;
+    return &CStringChecker::evalStrcat;
   else if (C.isCLibraryFunction(FDecl, "strncat"))
-    evalFunction =  &CStringChecker::evalStrncat;
+    return &CStringChecker::evalStrncat;
   else if (C.isCLibraryFunction(FDecl, "strlcat"))
-    evalFunction =  &CStringChecker::evalStrlcat;
+    return &CStringChecker::evalStrlcat;
   else if (C.isCLibraryFunction(FDecl, "strlen"))
-    evalFunction =  &CStringChecker::evalstrLength;
+    return &CStringChecker::evalstrLength;
   else if (C.isCLibraryFunction(FDecl, "strnlen"))
-    evalFunction =  &CStringChecker::evalstrnLength;
+    return &CStringChecker::evalstrnLength;
   else if (C.isCLibraryFunction(FDecl, "strcmp"))
-    evalFunction =  &CStringChecker::evalStrcmp;
+    return &CStringChecker::evalStrcmp;
   else if (C.isCLibraryFunction(FDecl, "strncmp"))
-    evalFunction =  &CStringChecker::evalStrncmp;
+    return &CStringChecker::evalStrncmp;
   else if (C.isCLibraryFunction(FDecl, "strcasecmp"))
-    evalFunction =  &CStringChecker::evalStrcasecmp;
+    return &CStringChecker::evalStrcasecmp;
   else if (C.isCLibraryFunction(FDecl, "strncasecmp"))
-    evalFunction =  &CStringChecker::evalStrncasecmp;
+    return &CStringChecker::evalStrncasecmp;
   else if (C.isCLibraryFunction(FDecl, "strsep"))
-    evalFunction =  &CStringChecker::evalStrsep;
+    return &CStringChecker::evalStrsep;
   else if (C.isCLibraryFunction(FDecl, "bcopy"))
-    evalFunction =  &CStringChecker::evalBcopy;
+    return &CStringChecker::evalBcopy;
   else if (C.isCLibraryFunction(FDecl, "bcmp"))
-    evalFunction =  &CStringChecker::evalMemcmp;
-  else if (isCPPStdLibraryFunction(FDecl, "copy"))
-    evalFunction =  &CStringChecker::evalStdCopy;
-  else if (isCPPStdLibraryFunction(FDecl, "copy_backward"))
-    evalFunction =  &CStringChecker::evalStdCopyBackward;
+    return &CStringChecker::evalMemcmp;
   else if (C.isCLibraryFunction(FDecl, "bzero") ||
-    C.isCLibraryFunction(FDecl, "explicit_bzero"))
-    evalFunction =  &CStringChecker::evalBzero;
+           C.isCLibraryFunction(FDecl, "explicit_bzero"))
+    return &CStringChecker::evalBzero;
+
+  return nullptr;
+}
+
+bool CStringChecker::evalCall(const CallExpr *CE, CheckerContext &C) const {
+
+  FnCheck evalFunction = identifyCall(CE, C);
 
   // If the callee isn't a string function, let another checker handle it.
   if (!evalFunction)