| //==- 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 "clang/Basic/TargetInfo.h" |
| #include "clang/Analysis/PathSensitive/BugReporter.h" |
| #include "clang/Analysis/LocalCheckers.h" |
| #include "clang/AST/StmtVisitor.h" |
| #include "llvm/Support/raw_ostream.h" |
| |
| using namespace clang; |
| |
| static bool isArc4RandomAvailable(const ASTContext &Ctx) { |
| const llvm::Triple &T = Ctx.Target.getTriple(); |
| return T.getVendor() == llvm::Triple::Apple || |
| T.getOS() == llvm::Triple::FreeBSD; |
| } |
| |
| namespace { |
| class WalkAST : public StmtVisitor<WalkAST> { |
| BugReporter &BR; |
| IdentifierInfo *II_gets; |
| IdentifierInfo *II_getpw; |
| IdentifierInfo *II_mktemp; |
| enum { num_rands = 9 }; |
| IdentifierInfo *II_rand[num_rands]; |
| IdentifierInfo *II_random; |
| enum { num_setids = 6 }; |
| IdentifierInfo *II_setid[num_setids]; |
| |
| const bool CheckRand; |
| |
| public: |
| WalkAST(BugReporter &br) : BR(br), |
| II_gets(0), II_getpw(0), II_mktemp(0), |
| II_rand(), II_random(0), II_setid(), |
| CheckRand(isArc4RandomAvailable(BR.getContext())) {} |
| |
| // 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. |
| IdentifierInfo *GetIdentifier(IdentifierInfo *& II, const char *str); |
| |
| // 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_rand(const CallExpr *CE, const FunctionDecl *FD); |
| void CheckCall_random(const CallExpr *CE, const FunctionDecl *FD); |
| void CheckUncheckedReturnValue(CallExpr *CE); |
| }; |
| } // end anonymous namespace |
| |
| //===----------------------------------------------------------------------===// |
| // Helper methods. |
| //===----------------------------------------------------------------------===// |
| |
| IdentifierInfo *WalkAST::GetIdentifier(IdentifierInfo *& II, const char *str) { |
| if (!II) |
| II = &BR.getContext().Idents.get(str); |
| |
| return II; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // 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) { |
| if (const FunctionDecl *FD = CE->getDirectCallee()) { |
| CheckCall_gets(CE, FD); |
| CheckCall_getpw(CE, FD); |
| CheckCall_mktemp(CE, FD); |
| if (CheckRand) { |
| CheckCall_rand(CE, FD); |
| CheckCall_random(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<CallExpr>(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: <rdar://problem/6336718> |
| // 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<BinaryOperator>(expr)) { |
| if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() || |
| B->getOpcode() == BinaryOperator::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<DeclRefExpr>(expr)) { |
| const NamedDecl *ND = DR->getDecl(); |
| return ND == x || ND == y ? DR : NULL; |
| } |
| |
| if (const UnaryOperator *U = dyn_cast<UnaryOperator>(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) { |
| // 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<BinaryOperator>(condition); |
| |
| if (!B) |
| return; |
| |
| // Is this a comparison? |
| if (!(B->isRelationalOp() || B->isEqualityOp())) |
| return; |
| |
| // Are we comparing variables? |
| const DeclRefExpr *drLHS = dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParens()); |
| const DeclRefExpr *drRHS = dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParens()); |
| |
| // Does at least one of the variables have a floating point type? |
| drLHS = drLHS && drLHS->getType()->isFloatingType() ? drLHS : NULL; |
| drRHS = drRHS && drRHS->getType()->isFloatingType() ? drRHS : NULL; |
| |
| if (!drLHS && !drRHS) |
| return; |
| |
| const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : NULL; |
| const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(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. |
| const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS; |
| |
| llvm::SmallVector<SourceRange, 2> ranges; |
| std::string sbuf; |
| llvm::raw_string_ostream os(sbuf); |
| |
| os << "Variable '" << drCond->getDecl()->getNameAsCString() |
| << "' 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"; |
| BR.EmitBasicReport(bugType, "Security", os.str(), |
| FS->getLocStart(), ranges.data(), ranges.size()); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Check: Any use of 'gets' is insecure. |
| // Originally: <rdar://problem/6335715> |
| // 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 (FD->getIdentifier() != GetIdentifier(II_gets, "gets")) |
| return; |
| |
| const FunctionProtoType *FPT = dyn_cast<FunctionProtoType>(FD->getType()); |
| if (!FPT) |
| return; |
| |
| // Verify that the function takes a single argument. |
| if (FPT->getNumArgs() != 1) |
| return; |
| |
| // Is the argument a 'char*'? |
| const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0)); |
| if (!PT) |
| return; |
| |
| if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) |
| return; |
| |
| // Issue a warning. |
| SourceRange R = CE->getCallee()->getSourceRange(); |
| BR.EmitBasicReport("Potential buffer overflow in call to 'gets'", |
| "Security", |
| "Call to function 'gets' is extremely insecure as it can " |
| "always result in a buffer overflow", |
| CE->getLocStart(), &R, 1); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Check: Any use of 'getpwd' is insecure. |
| // CWE-477: Use of Obsolete Functions |
| //===----------------------------------------------------------------------===// |
| |
| void WalkAST::CheckCall_getpw(const CallExpr *CE, const FunctionDecl *FD) { |
| if (FD->getIdentifier() != GetIdentifier(II_getpw, "getpw")) |
| return; |
| |
| const FunctionProtoType *FPT = dyn_cast<FunctionProtoType>(FD->getType()); |
| 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)->isIntegerType()) |
| return; |
| |
| // Verify the second argument type is char*. |
| const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(1)); |
| if (!PT) |
| return; |
| |
| if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) |
| return; |
| |
| // Issue a warning. |
| SourceRange R = CE->getCallee()->getSourceRange(); |
| BR.EmitBasicReport("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().", |
| CE->getLocStart(), &R, 1); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // 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 (FD->getIdentifier() != GetIdentifier(II_mktemp, "mktemp")) |
| return; |
| |
| const FunctionProtoType *FPT = dyn_cast<FunctionProtoType>(FD->getType()); |
| if(!FPT) |
| return; |
| |
| // Verify that the funcion takes a single argument. |
| if (FPT->getNumArgs() != 1) |
| return; |
| |
| // Verify that the argument is Pointer Type. |
| const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0)); |
| if (!PT) |
| return; |
| |
| // Verify that the argument is a 'char*'. |
| if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) |
| return; |
| |
| // Issue a waring. |
| SourceRange R = CE->getCallee()->getSourceRange(); |
| BR.EmitBasicReport("Potential insecure temporary file in call 'mktemp'", |
| "Security", |
| "Call to function 'mktemp' is insecure as it always " |
| "creates or uses insecure temporary file", |
| CE->getLocStart(), &R, 1); |
| } |
| |
| |
| //===----------------------------------------------------------------------===// |
| // Check: Linear congruent random number generators should not be used |
| // Originally: <rdar://problem/63371000> |
| // CWE-338: Use of cryptographically weak prng |
| //===----------------------------------------------------------------------===// |
| |
| void WalkAST::CheckCall_rand(const CallExpr *CE, const FunctionDecl *FD) { |
| if (II_rand[0] == NULL) { |
| // This check applies to these functions |
| static const char * const identifiers[num_rands] = { |
| "drand48", "erand48", "jrand48", "lrand48", "mrand48", "nrand48", |
| "lcong48", |
| "rand", "rand_r" |
| }; |
| |
| for (size_t i = 0; i < num_rands; i++) |
| II_rand[i] = &BR.getContext().Idents.get(identifiers[i]); |
| } |
| |
| const IdentifierInfo *id = FD->getIdentifier(); |
| size_t identifierid; |
| |
| for (identifierid = 0; identifierid < num_rands; identifierid++) |
| if (id == II_rand[identifierid]) |
| break; |
| |
| if (identifierid >= num_rands) |
| return; |
| |
| const FunctionProtoType *FTP = dyn_cast<FunctionProtoType>(FD->getType()); |
| if (!FTP) |
| return; |
| |
| if (FTP->getNumArgs() == 1) { |
| // Is the argument an 'unsigned short *'? |
| // (Actually any integer type is allowed.) |
| const PointerType *PT = dyn_cast<PointerType>(FTP->getArgType(0)); |
| if (!PT) |
| return; |
| |
| if (! PT->getPointeeType()->isIntegerType()) |
| return; |
| } |
| else if (FTP->getNumArgs() != 0) |
| return; |
| |
| // Issue a warning. |
| std::string buf1; |
| llvm::raw_string_ostream os1(buf1); |
| os1 << "'" << FD->getNameAsString() << "' is a poor random number generator"; |
| |
| std::string buf2; |
| llvm::raw_string_ostream os2(buf2); |
| os2 << "Function '" << FD->getNameAsString() |
| << "' is obsolete because it implements a poor random number generator." |
| << " Use 'arc4random' instead"; |
| |
| SourceRange R = CE->getCallee()->getSourceRange(); |
| |
| BR.EmitBasicReport(os1.str(), "Security", os2.str(), |
| CE->getLocStart(), &R, 1); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Check: 'random' should not be used |
| // Originally: <rdar://problem/63371000> |
| //===----------------------------------------------------------------------===// |
| |
| void WalkAST::CheckCall_random(const CallExpr *CE, const FunctionDecl *FD) { |
| if (FD->getIdentifier() != GetIdentifier(II_random, "random")) |
| return; |
| |
| const FunctionProtoType *FTP = dyn_cast<FunctionProtoType>(FD->getType()); |
| if (!FTP) |
| return; |
| |
| // Verify that the function takes no argument. |
| if (FTP->getNumArgs() != 0) |
| return; |
| |
| // Issue a warning. |
| SourceRange R = CE->getCallee()->getSourceRange(); |
| BR.EmitBasicReport("'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", |
| CE->getLocStart(), &R, 1); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Check: Should check whether privileges are dropped successfully. |
| // Originally: <rdar://problem/6337132> |
| //===----------------------------------------------------------------------===// |
| |
| void WalkAST::CheckUncheckedReturnValue(CallExpr *CE) { |
| 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 = dyn_cast<FunctionProtoType>(FD->getType()); |
| 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)->isIntegerType()) |
| return; |
| |
| // Issue a warning. |
| std::string buf1; |
| llvm::raw_string_ostream os1(buf1); |
| os1 << "Return value is not checked in call to '" << FD->getNameAsString() |
| << "'"; |
| |
| std::string buf2; |
| llvm::raw_string_ostream os2(buf2); |
| os2 << "The return value from the call to '" << FD->getNameAsString() |
| << "' is not checked. If an error occurs in '" |
| << FD->getNameAsString() |
| << "', the following code may execute with unexpected privileges"; |
| |
| SourceRange R = CE->getCallee()->getSourceRange(); |
| |
| BR.EmitBasicReport(os1.str(), "Security", os2.str(), |
| CE->getLocStart(), &R, 1); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Entry point for check. |
| //===----------------------------------------------------------------------===// |
| |
| void clang::CheckSecuritySyntaxOnly(const Decl *D, BugReporter &BR) { |
| WalkAST walker(BR); |
| walker.Visit(D->getBody()); |
| } |