[analyzer] Add checks for common anti-patterns in strncat.
(Since this is syntax only, might be a good candidate for turning into a
compiler warning.)
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149407 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp b/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp
new file mode 100644
index 0000000..4f7643e
--- /dev/null
+++ b/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp
@@ -0,0 +1,190 @@
+//== CStringSyntaxChecker.cpp - CoreFoundation containers API *- C++ -*-==//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// An AST checker that looks for common pitfalls when using C string APIs.
+// - Identifies erroneous patterns in the last argument to strncat - the number
+// of bytes to copy.
+//
+//===----------------------------------------------------------------------===//
+#include "ClangSACheckers.h"
+#include "clang/Analysis/AnalysisContext.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/OperationKinds.h"
+#include "clang/AST/StmtVisitor.h"
+#include "clang/Basic/TargetInfo.h"
+#include "clang/Basic/TypeTraits.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+class WalkAST: public StmtVisitor<WalkAST> {
+ BugReporter &BR;
+ AnalysisDeclContext* AC;
+ ASTContext &ASTC;
+
+ /// Check if two expressions refer to the same declaration.
+ inline bool sameDecl(const Expr *A1, const Expr *A2) {
+ if (const DeclRefExpr *D1 = dyn_cast<DeclRefExpr>(A1->IgnoreParenCasts()))
+ if (const DeclRefExpr *D2 = dyn_cast<DeclRefExpr>(A2->IgnoreParenCasts()))
+ return D1->getDecl() == D2->getDecl();
+ return false;
+ }
+
+ /// Check if the expression E is a sizeof(WithArg).
+ inline bool isSizeof(const Expr *E, const Expr *WithArg) {
+ if (const UnaryExprOrTypeTraitExpr *UE =
+ dyn_cast<UnaryExprOrTypeTraitExpr>(E))
+ if (UE->getKind() == UETT_SizeOf)
+ return sameDecl(UE->getArgumentExpr(), WithArg);
+ return false;
+ }
+
+ /// Check if the expression E is a strlen(WithArg).
+ inline bool isStrlen(const Expr *E, const Expr *WithArg) {
+ if (const CallExpr *CE = dyn_cast<CallExpr>(E)) {
+ const FunctionDecl *FD = CE->getDirectCallee();
+ if (!FD)
+ return false;
+ return (CheckerContext::isCLibraryFunction(FD, "strlen", ASTC)
+ && sameDecl(CE->getArg(0), WithArg));
+ }
+ return false;
+ }
+
+ /// Check if the expression is an integer literal with value 1.
+ inline bool isOne(const Expr *E) {
+ if (const IntegerLiteral *IL = dyn_cast<IntegerLiteral>(E))
+ return (IL->getValue().isIntN(1));
+ return false;
+ }
+
+ inline StringRef getPrintableName(const Expr *E) {
+ if (const DeclRefExpr *D = dyn_cast<DeclRefExpr>(E->IgnoreParenCasts()))
+ return D->getDecl()->getName();
+ return StringRef();
+ }
+
+ /// Identify erroneous patterns in the last argument to strncat - the number
+ /// of bytes to copy.
+ bool containsBadStrncatPattern(const CallExpr *CE);
+
+public:
+ WalkAST(BugReporter &br, AnalysisDeclContext* ac) :
+ BR(br), AC(ac), ASTC(AC->getASTContext()) {
+ }
+
+ // Statement visitor methods.
+ void VisitChildren(Stmt *S);
+ void VisitStmt(Stmt *S) {
+ VisitChildren(S);
+ }
+ void VisitCallExpr(CallExpr *CE);
+};
+} // end anonymous namespace
+
+// The correct size argument should look like following:
+// strncat(dst, src, sizeof(dst) - strlen(dest) - 1);
+// We look for the following anti-patterns:
+// - strncat(dst, src, sizeof(dst) - strlen(dst));
+// - strncat(dst, src, sizeof(dst) - 1);
+// - strncat(dst, src, sizeof(dst));
+bool WalkAST::containsBadStrncatPattern(const CallExpr *CE) {
+ const Expr *DstArg = CE->getArg(0);
+ const Expr *SrcArg = CE->getArg(1);
+ const Expr *LenArg = CE->getArg(2);
+
+ // Identify wrong size expressions, which are commonly used instead.
+ if (const BinaryOperator *BE =
+ dyn_cast<BinaryOperator>(LenArg->IgnoreParenCasts())) {
+ // - sizeof(dst) - strlen(dst)
+ if (BE->getOpcode() == BO_Sub) {
+ const Expr *L = BE->getLHS();
+ const Expr *R = BE->getRHS();
+ if (isSizeof(L, DstArg) && isStrlen(R, DstArg))
+ return true;
+
+ // - sizeof(dst) - 1
+ if (isSizeof(L, DstArg) && isOne(R->IgnoreParenCasts()))
+ return true;
+ }
+ }
+ // - sizeof(dst)
+ if (isSizeof(LenArg, DstArg))
+ return true;
+
+ // - sizeof(src)
+ if (isSizeof(LenArg, SrcArg))
+ return true;
+ return false;
+}
+
+void WalkAST::VisitCallExpr(CallExpr *CE) {
+ const FunctionDecl *FD = CE->getDirectCallee();
+ if (!FD)
+ return;
+
+ if (CheckerContext::isCLibraryFunction(FD, "strncat", ASTC)) {
+ if (containsBadStrncatPattern(CE)) {
+ const Expr *DstArg = CE->getArg(0);
+ const Expr *LenArg = CE->getArg(2);
+ SourceRange R = LenArg->getSourceRange();
+ PathDiagnosticLocation Loc =
+ PathDiagnosticLocation::createBegin(LenArg, BR.getSourceManager(), AC);
+
+ StringRef DstName = getPrintableName(DstArg);
+
+ llvm::SmallString<256> S;
+ llvm::raw_svector_ostream os(S);
+ os << "Potential buffer overflow. ";
+ if (!DstName.empty()) {
+ os << "Replace with 'sizeof(" << DstName << ") "
+ "- strlen(" << DstName <<") - 1'";
+ os << " or u";
+ } else
+ os << "U";
+ os << "se a safer 'strlcat' API";
+
+ BR.EmitBasicReport("Anti-pattern in the argument", "C String API",
+ os.str(), Loc, &R, 1);
+ }
+ }
+
+ // Recurse and check children.
+ VisitChildren(CE);
+}
+
+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);
+}
+
+namespace {
+class CStringSyntaxChecker: public Checker<check::ASTCodeBody> {
+public:
+
+ void checkASTCodeBody(const Decl *D, AnalysisManager& Mgr,
+ BugReporter &BR) const {
+ WalkAST walker(BR, Mgr.getAnalysisDeclContext(D));
+ walker.Visit(D->getBody());
+ }
+};
+}
+
+void ento::registerCStringSyntaxChecker(CheckerManager &mgr) {
+ mgr.registerChecker<CStringSyntaxChecker>();
+}
+