//==- CheckSecuritySyntaxOnly.cpp - Basic security checks --------*- C++ -*-==// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file defines a set of flow-insensitive security checks. // //===----------------------------------------------------------------------===// #include "ClangSACheckers.h" #include "clang/AST/StmtVisitor.h" #include "clang/Analysis/AnalysisContext.h" #include "clang/Basic/TargetInfo.h" #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h" #include "clang/StaticAnalyzer/Core/Checker.h" #include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h" #include "llvm/ADT/SmallString.h" #include "llvm/ADT/StringSwitch.h" #include "llvm/Support/raw_ostream.h" using namespace clang; using namespace ento; static bool isArc4RandomAvailable(const ASTContext &Ctx) { const llvm::Triple &T = Ctx.getTargetInfo().getTriple(); return T.getVendor() == llvm::Triple::Apple || T.getOS() == llvm::Triple::FreeBSD || T.getOS() == llvm::Triple::NetBSD || T.getOS() == llvm::Triple::OpenBSD || T.getOS() == llvm::Triple::Bitrig || T.getOS() == llvm::Triple::DragonFly; } namespace { struct ChecksFilter { DefaultBool check_gets; DefaultBool check_getpw; DefaultBool check_mktemp; DefaultBool check_mkstemp; DefaultBool check_strcpy; DefaultBool check_rand; DefaultBool check_vfork; DefaultBool check_FloatLoopCounter; DefaultBool check_UncheckedReturn; }; class WalkAST : public StmtVisitor { BugReporter &BR; AnalysisDeclContext* AC; enum { num_setids = 6 }; IdentifierInfo *II_setid[num_setids]; const bool CheckRand; const ChecksFilter &filter; public: WalkAST(BugReporter &br, AnalysisDeclContext* ac, const ChecksFilter &f) : BR(br), AC(ac), II_setid(), CheckRand(isArc4RandomAvailable(BR.getContext())), filter(f) {} // Statement visitor methods. void VisitCallExpr(CallExpr *CE); void VisitForStmt(ForStmt *S); void VisitCompoundStmt (CompoundStmt *S); void VisitStmt(Stmt *S) { VisitChildren(S); } void VisitChildren(Stmt *S); // Helpers. bool checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD); typedef void (WalkAST::*FnCheck)(const CallExpr *, const FunctionDecl *); // Checker-specific methods. void checkLoopConditionForFloat(const ForStmt *FS); void checkCall_gets(const CallExpr *CE, const FunctionDecl *FD); void checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD); void checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD); void checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD); void checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD); void checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD); void checkCall_rand(const CallExpr *CE, const FunctionDecl *FD); void checkCall_random(const CallExpr *CE, const FunctionDecl *FD); void checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD); void checkUncheckedReturnValue(CallExpr *CE); }; } // end anonymous namespace //===----------------------------------------------------------------------===// // AST walking. //===----------------------------------------------------------------------===// void WalkAST::VisitChildren(Stmt *S) { for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I) if (Stmt *child = *I) Visit(child); } void WalkAST::VisitCallExpr(CallExpr *CE) { // Get the callee. const FunctionDecl *FD = CE->getDirectCallee(); if (!FD) return; // Get the name of the callee. If it's a builtin, strip off the prefix. IdentifierInfo *II = FD->getIdentifier(); if (!II) // if no identifier, not a simple C function return; StringRef Name = II->getName(); if (Name.startswith("__builtin_")) Name = Name.substr(10); // Set the evaluation function by switching on the callee name. FnCheck evalFunction = llvm::StringSwitch(Name) .Case("gets", &WalkAST::checkCall_gets) .Case("getpw", &WalkAST::checkCall_getpw) .Case("mktemp", &WalkAST::checkCall_mktemp) .Case("mkstemp", &WalkAST::checkCall_mkstemp) .Case("mkdtemp", &WalkAST::checkCall_mkstemp) .Case("mkstemps", &WalkAST::checkCall_mkstemp) .Cases("strcpy", "__strcpy_chk", &WalkAST::checkCall_strcpy) .Cases("strcat", "__strcat_chk", &WalkAST::checkCall_strcat) .Case("drand48", &WalkAST::checkCall_rand) .Case("erand48", &WalkAST::checkCall_rand) .Case("jrand48", &WalkAST::checkCall_rand) .Case("lrand48", &WalkAST::checkCall_rand) .Case("mrand48", &WalkAST::checkCall_rand) .Case("nrand48", &WalkAST::checkCall_rand) .Case("lcong48", &WalkAST::checkCall_rand) .Case("rand", &WalkAST::checkCall_rand) .Case("rand_r", &WalkAST::checkCall_rand) .Case("random", &WalkAST::checkCall_random) .Case("vfork", &WalkAST::checkCall_vfork) .Default(NULL); // If the callee isn't defined, it is not of security concern. // Check and evaluate the call. if (evalFunction) (this->*evalFunction)(CE, FD); // Recurse and check children. VisitChildren(CE); } void WalkAST::VisitCompoundStmt(CompoundStmt *S) { for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I) if (Stmt *child = *I) { if (CallExpr *CE = dyn_cast(child)) checkUncheckedReturnValue(CE); Visit(child); } } void WalkAST::VisitForStmt(ForStmt *FS) { checkLoopConditionForFloat(FS); // Recurse and check children. VisitChildren(FS); } //===----------------------------------------------------------------------===// // Check: floating poing variable used as loop counter. // Originally: // Implements: CERT security coding advisory FLP-30. //===----------------------------------------------------------------------===// static const DeclRefExpr* getIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) { expr = expr->IgnoreParenCasts(); if (const BinaryOperator *B = dyn_cast(expr)) { if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() || B->getOpcode() == BO_Comma)) return NULL; if (const DeclRefExpr *lhs = getIncrementedVar(B->getLHS(), x, y)) return lhs; if (const DeclRefExpr *rhs = getIncrementedVar(B->getRHS(), x, y)) return rhs; return NULL; } if (const DeclRefExpr *DR = dyn_cast(expr)) { const NamedDecl *ND = DR->getDecl(); return ND == x || ND == y ? DR : NULL; } if (const UnaryOperator *U = dyn_cast(expr)) return U->isIncrementDecrementOp() ? getIncrementedVar(U->getSubExpr(), x, y) : NULL; return NULL; } /// CheckLoopConditionForFloat - This check looks for 'for' statements that /// use a floating point variable as a loop counter. /// CERT: FLP30-C, FLP30-CPP. /// void WalkAST::checkLoopConditionForFloat(const ForStmt *FS) { if (!filter.check_FloatLoopCounter) return; // Does the loop have a condition? const Expr *condition = FS->getCond(); if (!condition) return; // Does the loop have an increment? const Expr *increment = FS->getInc(); if (!increment) return; // Strip away '()' and casts. condition = condition->IgnoreParenCasts(); increment = increment->IgnoreParenCasts(); // Is the loop condition a comparison? const BinaryOperator *B = dyn_cast(condition); if (!B) return; // Is this a comparison? if (!(B->isRelationalOp() || B->isEqualityOp())) return; // Are we comparing variables? const DeclRefExpr *drLHS = dyn_cast(B->getLHS()->IgnoreParenLValueCasts()); const DeclRefExpr *drRHS = dyn_cast(B->getRHS()->IgnoreParenLValueCasts()); // Does at least one of the variables have a floating point type? drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : NULL; drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : NULL; if (!drLHS && !drRHS) return; const VarDecl *vdLHS = drLHS ? dyn_cast(drLHS->getDecl()) : NULL; const VarDecl *vdRHS = drRHS ? dyn_cast(drRHS->getDecl()) : NULL; if (!vdLHS && !vdRHS) return; // Does either variable appear in increment? const DeclRefExpr *drInc = getIncrementedVar(increment, vdLHS, vdRHS); if (!drInc) return; // Emit the error. First figure out which DeclRefExpr in the condition // referenced the compared variable. assert(drInc->getDecl()); const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS; SmallVector ranges; SmallString<256> sbuf; llvm::raw_svector_ostream os(sbuf); os << "Variable '" << drCond->getDecl()->getName() << "' with floating point type '" << drCond->getType().getAsString() << "' should not be used as a loop counter"; ranges.push_back(drCond->getSourceRange()); ranges.push_back(drInc->getSourceRange()); const char *bugType = "Floating point variable used as loop counter"; PathDiagnosticLocation FSLoc = PathDiagnosticLocation::createBegin(FS, BR.getSourceManager(), AC); BR.EmitBasicReport(AC->getDecl(), bugType, "Security", os.str(), FSLoc, ranges); } //===----------------------------------------------------------------------===// // Check: Any use of 'gets' is insecure. // Originally: // Implements (part of): 300-BSI (buildsecurityin.us-cert.gov) // CWE-242: Use of Inherently Dangerous Function //===----------------------------------------------------------------------===// void WalkAST::checkCall_gets(const CallExpr *CE, const FunctionDecl *FD) { if (!filter.check_gets) return; const FunctionProtoType *FPT = FD->getType()->getAs(); if (!FPT) return; // Verify that the function takes a single argument. if (FPT->getNumArgs() != 1) return; // Is the argument a 'char*'? const PointerType *PT = FPT->getArgType(0)->getAs(); if (!PT) return; if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) return; // Issue a warning. PathDiagnosticLocation CELoc = PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC); BR.EmitBasicReport(AC->getDecl(), "Potential buffer overflow in call to 'gets'", "Security", "Call to function 'gets' is extremely insecure as it can " "always result in a buffer overflow", CELoc, CE->getCallee()->getSourceRange()); } //===----------------------------------------------------------------------===// // Check: Any use of 'getpwd' is insecure. // CWE-477: Use of Obsolete Functions //===----------------------------------------------------------------------===// void WalkAST::checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD) { if (!filter.check_getpw) return; const FunctionProtoType *FPT = FD->getType()->getAs(); if (!FPT) return; // Verify that the function takes two arguments. if (FPT->getNumArgs() != 2) return; // Verify the first argument type is integer. if (!FPT->getArgType(0)->isIntegralOrUnscopedEnumerationType()) return; // Verify the second argument type is char*. const PointerType *PT = FPT->getArgType(1)->getAs(); if (!PT) return; if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) return; // Issue a warning. PathDiagnosticLocation CELoc = PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC); BR.EmitBasicReport(AC->getDecl(), "Potential buffer overflow in call to 'getpw'", "Security", "The getpw() function is dangerous as it may overflow the " "provided buffer. It is obsoleted by getpwuid().", CELoc, CE->getCallee()->getSourceRange()); } //===----------------------------------------------------------------------===// // Check: Any use of 'mktemp' is insecure. It is obsoleted by mkstemp(). // CWE-377: Insecure Temporary File //===----------------------------------------------------------------------===// void WalkAST::checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) { if (!filter.check_mktemp) { // Fall back to the security check of looking for enough 'X's in the // format string, since that is a less severe warning. checkCall_mkstemp(CE, FD); return; } const FunctionProtoType *FPT = FD->getType()->getAs(); if(!FPT) return; // Verify that the function takes a single argument. if (FPT->getNumArgs() != 1) return; // Verify that the argument is Pointer Type. const PointerType *PT = FPT->getArgType(0)->getAs(); if (!PT) return; // Verify that the argument is a 'char*'. if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) return; // Issue a waring. PathDiagnosticLocation CELoc = PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC); BR.EmitBasicReport(AC->getDecl(), "Potential insecure temporary file in call 'mktemp'", "Security", "Call to function 'mktemp' is insecure as it always " "creates or uses insecure temporary file. Use 'mkstemp' " "instead", CELoc, CE->getCallee()->getSourceRange()); } //===----------------------------------------------------------------------===// // Check: Use of 'mkstemp', 'mktemp', 'mkdtemp' should contain at least 6 X's. //===----------------------------------------------------------------------===// void WalkAST::checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD) { if (!filter.check_mkstemp) return; StringRef Name = FD->getIdentifier()->getName(); std::pair ArgSuffix = llvm::StringSwitch >(Name) .Case("mktemp", std::make_pair(0,-1)) .Case("mkstemp", std::make_pair(0,-1)) .Case("mkdtemp", std::make_pair(0,-1)) .Case("mkstemps", std::make_pair(0,1)) .Default(std::make_pair(-1, -1)); assert(ArgSuffix.first >= 0 && "Unsupported function"); // Check if the number of arguments is consistent with out expectations. unsigned numArgs = CE->getNumArgs(); if ((signed) numArgs <= ArgSuffix.first) return; const StringLiteral *strArg = dyn_cast(CE->getArg((unsigned)ArgSuffix.first) ->IgnoreParenImpCasts()); // Currently we only handle string literals. It is possible to do better, // either by looking at references to const variables, or by doing real // flow analysis. if (!strArg || strArg->getCharByteWidth() != 1) return; // Count the number of X's, taking into account a possible cutoff suffix. StringRef str = strArg->getString(); unsigned numX = 0; unsigned n = str.size(); // Take into account the suffix. unsigned suffix = 0; if (ArgSuffix.second >= 0) { const Expr *suffixEx = CE->getArg((unsigned)ArgSuffix.second); llvm::APSInt Result; if (!suffixEx->EvaluateAsInt(Result, BR.getContext())) return; // FIXME: Issue a warning. if (Result.isNegative()) return; suffix = (unsigned) Result.getZExtValue(); n = (n > suffix) ? n - suffix : 0; } for (unsigned i = 0; i < n; ++i) if (str[i] == 'X') ++numX; if (numX >= 6) return; // Issue a warning. PathDiagnosticLocation CELoc = PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC); SmallString<512> buf; llvm::raw_svector_ostream out(buf); out << "Call to '" << Name << "' should have at least 6 'X's in the" " format string to be secure (" << numX << " 'X'"; if (numX != 1) out << 's'; out << " seen"; if (suffix) { out << ", " << suffix << " character"; if (suffix > 1) out << 's'; out << " used as a suffix"; } out << ')'; BR.EmitBasicReport(AC->getDecl(), "Insecure temporary file creation", "Security", out.str(), CELoc, strArg->getSourceRange()); } //===----------------------------------------------------------------------===// // Check: Any use of 'strcpy' is insecure. // // CWE-119: Improper Restriction of Operations within // the Bounds of a Memory Buffer //===----------------------------------------------------------------------===// void WalkAST::checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD) { if (!filter.check_strcpy) return; if (!checkCall_strCommon(CE, FD)) return; // Issue a warning. PathDiagnosticLocation CELoc = PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC); BR.EmitBasicReport(AC->getDecl(), "Potential insecure memory buffer bounds restriction in " "call 'strcpy'", "Security", "Call to function 'strcpy' is insecure as it does not " "provide bounding of the memory buffer. Replace " "unbounded copy functions with analogous functions that " "support length arguments such as 'strlcpy'. CWE-119.", CELoc, CE->getCallee()->getSourceRange()); } //===----------------------------------------------------------------------===// // Check: Any use of 'strcat' is insecure. // // CWE-119: Improper Restriction of Operations within // the Bounds of a Memory Buffer //===----------------------------------------------------------------------===// void WalkAST::checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD) { if (!filter.check_strcpy) return; if (!checkCall_strCommon(CE, FD)) return; // Issue a warning. PathDiagnosticLocation CELoc = PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC); BR.EmitBasicReport(AC->getDecl(), "Potential insecure memory buffer bounds restriction in " "call 'strcat'", "Security", "Call to function 'strcat' is insecure as it does not " "provide bounding of the memory buffer. Replace " "unbounded copy functions with analogous functions that " "support length arguments such as 'strlcat'. CWE-119.", CELoc, CE->getCallee()->getSourceRange()); } //===----------------------------------------------------------------------===// // Common check for str* functions with no bounds parameters. //===----------------------------------------------------------------------===// bool WalkAST::checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD) { const FunctionProtoType *FPT = FD->getType()->getAs(); if (!FPT) return false; // Verify the function takes two arguments, three in the _chk version. int numArgs = FPT->getNumArgs(); if (numArgs != 2 && numArgs != 3) return false; // Verify the type for both arguments. for (int i = 0; i < 2; i++) { // Verify that the arguments are pointers. const PointerType *PT = FPT->getArgType(i)->getAs(); if (!PT) return false; // Verify that the argument is a 'char*'. if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) return false; } return true; } //===----------------------------------------------------------------------===// // Check: Linear congruent random number generators should not be used // Originally: // CWE-338: Use of cryptographically weak prng //===----------------------------------------------------------------------===// void WalkAST::checkCall_rand(const CallExpr *CE, const FunctionDecl *FD) { if (!filter.check_rand || !CheckRand) return; const FunctionProtoType *FTP = FD->getType()->getAs(); if (!FTP) return; if (FTP->getNumArgs() == 1) { // Is the argument an 'unsigned short *'? // (Actually any integer type is allowed.) const PointerType *PT = FTP->getArgType(0)->getAs(); if (!PT) return; if (! PT->getPointeeType()->isIntegralOrUnscopedEnumerationType()) return; } else if (FTP->getNumArgs() != 0) return; // Issue a warning. SmallString<256> buf1; llvm::raw_svector_ostream os1(buf1); os1 << '\'' << *FD << "' is a poor random number generator"; SmallString<256> buf2; llvm::raw_svector_ostream os2(buf2); os2 << "Function '" << *FD << "' is obsolete because it implements a poor random number generator." << " Use 'arc4random' instead"; PathDiagnosticLocation CELoc = PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC); BR.EmitBasicReport(AC->getDecl(), os1.str(), "Security", os2.str(), CELoc, CE->getCallee()->getSourceRange()); } //===----------------------------------------------------------------------===// // Check: 'random' should not be used // Originally: //===----------------------------------------------------------------------===// void WalkAST::checkCall_random(const CallExpr *CE, const FunctionDecl *FD) { if (!CheckRand || !filter.check_rand) return; const FunctionProtoType *FTP = FD->getType()->getAs(); if (!FTP) return; // Verify that the function takes no argument. if (FTP->getNumArgs() != 0) return; // Issue a warning. PathDiagnosticLocation CELoc = PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC); BR.EmitBasicReport(AC->getDecl(), "'random' is not a secure random number generator", "Security", "The 'random' function produces a sequence of values that " "an adversary may be able to predict. Use 'arc4random' " "instead", CELoc, CE->getCallee()->getSourceRange()); } //===----------------------------------------------------------------------===// // Check: 'vfork' should not be used. // POS33-C: Do not use vfork(). //===----------------------------------------------------------------------===// void WalkAST::checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD) { if (!filter.check_vfork) return; // All calls to vfork() are insecure, issue a warning. PathDiagnosticLocation CELoc = PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC); BR.EmitBasicReport(AC->getDecl(), "Potential insecure implementation-specific behavior in " "call 'vfork'", "Security", "Call to function 'vfork' is insecure as it can lead to " "denial of service situations in the parent process. " "Replace calls to vfork with calls to the safer " "'posix_spawn' function", CELoc, CE->getCallee()->getSourceRange()); } //===----------------------------------------------------------------------===// // Check: Should check whether privileges are dropped successfully. // Originally: //===----------------------------------------------------------------------===// void WalkAST::checkUncheckedReturnValue(CallExpr *CE) { if (!filter.check_UncheckedReturn) return; const FunctionDecl *FD = CE->getDirectCallee(); if (!FD) return; if (II_setid[0] == NULL) { static const char * const identifiers[num_setids] = { "setuid", "setgid", "seteuid", "setegid", "setreuid", "setregid" }; for (size_t i = 0; i < num_setids; i++) II_setid[i] = &BR.getContext().Idents.get(identifiers[i]); } const IdentifierInfo *id = FD->getIdentifier(); size_t identifierid; for (identifierid = 0; identifierid < num_setids; identifierid++) if (id == II_setid[identifierid]) break; if (identifierid >= num_setids) return; const FunctionProtoType *FTP = FD->getType()->getAs(); if (!FTP) return; // Verify that the function takes one or two arguments (depending on // the function). if (FTP->getNumArgs() != (identifierid < 4 ? 1 : 2)) return; // The arguments must be integers. for (unsigned i = 0; i < FTP->getNumArgs(); i++) if (! FTP->getArgType(i)->isIntegralOrUnscopedEnumerationType()) return; // Issue a warning. SmallString<256> buf1; llvm::raw_svector_ostream os1(buf1); os1 << "Return value is not checked in call to '" << *FD << '\''; SmallString<256> buf2; llvm::raw_svector_ostream os2(buf2); os2 << "The return value from the call to '" << *FD << "' is not checked. If an error occurs in '" << *FD << "', the following code may execute with unexpected privileges"; PathDiagnosticLocation CELoc = PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC); BR.EmitBasicReport(AC->getDecl(), os1.str(), "Security", os2.str(), CELoc, CE->getCallee()->getSourceRange()); } //===----------------------------------------------------------------------===// // SecuritySyntaxChecker //===----------------------------------------------------------------------===// namespace { class SecuritySyntaxChecker : public Checker { public: ChecksFilter filter; void checkASTCodeBody(const Decl *D, AnalysisManager& mgr, BugReporter &BR) const { WalkAST walker(BR, mgr.getAnalysisDeclContext(D), filter); walker.Visit(D->getBody()); } }; } #define REGISTER_CHECKER(name) \ void ento::register##name(CheckerManager &mgr) {\ mgr.registerChecker()->filter.check_##name = true;\ } REGISTER_CHECKER(gets) REGISTER_CHECKER(getpw) REGISTER_CHECKER(mkstemp) REGISTER_CHECKER(mktemp) REGISTER_CHECKER(strcpy) REGISTER_CHECKER(rand) REGISTER_CHECKER(vfork) REGISTER_CHECKER(FloatLoopCounter) REGISTER_CHECKER(UncheckedReturn)