1 files changed, 296 insertions, 0 deletions
diff --git a/contrib/llvm-project/clang/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp b/contrib/llvm-project/clang/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp
new file mode 100644
index 000000000000..d84fcc69a492
--- /dev/null
+++ b/contrib/llvm-project/clang/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp
@@ -0,0 +1,296 @@
+//== CStringSyntaxChecker.cpp - CoreFoundation containers API *- C++ -*-==//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// 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 "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/OperationKinds.h"
+#include "clang/AST/StmtVisitor.h"
+#include "clang/Analysis/AnalysisDeclContext.h"
+#include "clang/Basic/TargetInfo.h"
+#include "clang/Basic/TypeTraits.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+class WalkAST: public StmtVisitor<WalkAST> {
+  const CheckerBase *Checker;
+  BugReporter &BR;
+  AnalysisDeclContext* AC;
+
+  /// Check if two expressions refer to the same declaration.
+  bool sameDecl(const Expr *A1, const Expr *A2) {
+    if (const auto *D1 = dyn_cast<DeclRefExpr>(A1->IgnoreParenCasts()))
+      if (const auto *D2 = dyn_cast<DeclRefExpr>(A2->IgnoreParenCasts()))
+        return D1->getDecl() == D2->getDecl();
+    return false;
+  }
+
+  /// Check if the expression E is a sizeof(WithArg).
+  bool isSizeof(const Expr *E, const Expr *WithArg) {
+    if (const auto *UE = dyn_cast<UnaryExprOrTypeTraitExpr>(E))
+      if (UE->getKind() == UETT_SizeOf && !UE->isArgumentType())
+        return sameDecl(UE->getArgumentExpr(), WithArg);
+    return false;
+  }
+
+  /// Check if the expression E is a strlen(WithArg).
+  bool isStrlen(const Expr *E, const Expr *WithArg) {
+    if (const auto *CE = dyn_cast<CallExpr>(E)) {
+      const FunctionDecl *FD = CE->getDirectCallee();
+      if (!FD)
+        return false;
+      return (CheckerContext::isCLibraryFunction(FD, "strlen") &&
+              sameDecl(CE->getArg(0), WithArg));
+    }
+    return false;
+  }
+
+  /// Check if the expression is an integer literal with value 1.
+  bool isOne(const Expr *E) {
+    if (const auto *IL = dyn_cast<IntegerLiteral>(E))
+      return (IL->getValue().isIntN(1));
+    return false;
+  }
+
+  StringRef getPrintableName(const Expr *E) {
+    if (const auto *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);
+
+  /// Identify erroneous patterns in the last argument to strlcpy - the number
+  /// of bytes to copy.
+  /// The bad pattern checked is when the size is known
+  /// to be larger than the destination can handle.
+  ///   char dst[2];
+  ///   size_t cpy = 4;
+  ///   strlcpy(dst, "abcd", sizeof("abcd") - 1);
+  ///   strlcpy(dst, "abcd", 4);
+  ///   strlcpy(dst + 3, "abcd", 2);
+  ///   strlcpy(dst, "abcd", cpy);
+  /// Identify erroneous patterns in the last argument to strlcat - the number
+  /// of bytes to copy.
+  /// The bad pattern checked is when the last argument is basically
+  /// pointing to the destination buffer size or argument larger or
+  /// equal to.
+  ///   char dst[2];
+  ///   strlcat(dst, src2, sizeof(dst));
+  ///   strlcat(dst, src2, 2);
+  ///   strlcat(dst, src2, 10);
+  bool containsBadStrlcpyStrlcatPattern(const CallExpr *CE);
+
+public:
+  WalkAST(const CheckerBase *Checker, BugReporter &BR, AnalysisDeclContext *AC)
+      : Checker(Checker), BR(BR), AC(AC) {}
+
+  // 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) {
+  if (CE->getNumArgs() != 3)
+    return false;
+  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 auto *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;
+}
+
+bool WalkAST::containsBadStrlcpyStrlcatPattern(const CallExpr *CE) {
+  if (CE->getNumArgs() != 3)
+    return false;
+  const Expr *DstArg = CE->getArg(0);
+  const Expr *LenArg = CE->getArg(2);
+
+  const auto *DstArgDRE = dyn_cast<DeclRefExpr>(DstArg->IgnoreParenImpCasts());
+  const auto *LenArgDRE =
+      dyn_cast<DeclRefExpr>(LenArg->IgnoreParenLValueCasts());
+  uint64_t DstOff = 0;
+  if (isSizeof(LenArg, DstArg))
+    return false;
+
+  // - size_t dstlen = sizeof(dst)
+  if (LenArgDRE) {
+    const auto *LenArgVal = dyn_cast<VarDecl>(LenArgDRE->getDecl());
+    // If it's an EnumConstantDecl instead, then we're missing out on something.
+    if (!LenArgVal) {
+      assert(isa<EnumConstantDecl>(LenArgDRE->getDecl()));
+      return false;
+    }
+    if (LenArgVal->getInit())
+      LenArg = LenArgVal->getInit();
+  }
+
+  // - integral value
+  // We try to figure out if the last argument is possibly longer
+  // than the destination can possibly handle if its size can be defined.
+  if (const auto *IL = dyn_cast<IntegerLiteral>(LenArg->IgnoreParenImpCasts())) {
+    uint64_t ILRawVal = IL->getValue().getZExtValue();
+
+    // Case when there is pointer arithmetic on the destination buffer
+    // especially when we offset from the base decreasing the
+    // buffer length accordingly.
+    if (!DstArgDRE) {
+      if (const auto *BE =
+              dyn_cast<BinaryOperator>(DstArg->IgnoreParenImpCasts())) {
+        DstArgDRE = dyn_cast<DeclRefExpr>(BE->getLHS()->IgnoreParenImpCasts());
+        if (BE->getOpcode() == BO_Add) {
+          if ((IL = dyn_cast<IntegerLiteral>(BE->getRHS()->IgnoreParenImpCasts()))) {
+            DstOff = IL->getValue().getZExtValue();
+          }
+        }
+      }
+    }
+    if (DstArgDRE) {
+      if (const auto *Buffer =
+              dyn_cast<ConstantArrayType>(DstArgDRE->getType())) {
+        ASTContext &C = BR.getContext();
+        uint64_t BufferLen = C.getTypeSize(Buffer) / 8;
+        auto RemainingBufferLen = BufferLen - DstOff;
+        if (RemainingBufferLen < ILRawVal)
+          return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+void WalkAST::VisitCallExpr(CallExpr *CE) {
+  const FunctionDecl *FD = CE->getDirectCallee();
+  if (!FD)
+    return;
+
+  if (CheckerContext::isCLibraryFunction(FD, "strncat")) {
+    if (containsBadStrncatPattern(CE)) {
+      const Expr *DstArg = CE->getArg(0);
+      const Expr *LenArg = CE->getArg(2);
+      PathDiagnosticLocation Loc =
+        PathDiagnosticLocation::createBegin(LenArg, BR.getSourceManager(), AC);
+
+      StringRef DstName = getPrintableName(DstArg);
+
+      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(FD, Checker, "Anti-pattern in the argument",
+                         "C String API", os.str(), Loc,
+                         LenArg->getSourceRange());
+    }
+  } else if (CheckerContext::isCLibraryFunction(FD, "strlcpy") ||
+             CheckerContext::isCLibraryFunction(FD, "strlcat")) {
+    if (containsBadStrlcpyStrlcatPattern(CE)) {
+      const Expr *DstArg = CE->getArg(0);
+      const Expr *LenArg = CE->getArg(2);
+      PathDiagnosticLocation Loc =
+        PathDiagnosticLocation::createBegin(LenArg, BR.getSourceManager(), AC);
+
+      StringRef DstName = getPrintableName(DstArg);
+
+      SmallString<256> S;
+      llvm::raw_svector_ostream os(S);
+      os << "The third argument allows to potentially copy more bytes than it should. ";
+      os << "Replace with the value ";
+      if (!DstName.empty())
+          os << "sizeof(" << DstName << ")";
+      else
+          os << "sizeof(<destination buffer>)";
+      os << " or lower";
+
+      BR.EmitBasicReport(FD, Checker, "Anti-pattern in the argument",
+              "C String API", os.str(), Loc,
+              LenArg->getSourceRange());
+    }
+  }
+
+  // Recurse and check children.
+  VisitChildren(CE);
+}
+
+void WalkAST::VisitChildren(Stmt *S) {
+  for (Stmt *Child : S->children())
+    if (Child)
+      Visit(Child);
+}
+
+namespace {
+class CStringSyntaxChecker: public Checker<check::ASTCodeBody> {
+public:
+
+  void checkASTCodeBody(const Decl *D, AnalysisManager& Mgr,
+      BugReporter &BR) const {
+    WalkAST walker(this, BR, Mgr.getAnalysisDeclContext(D));
+    walker.Visit(D->getBody());
+  }
+};
+}
+
+void ento::registerCStringSyntaxChecker(CheckerManager &mgr) {
+  mgr.registerChecker<CStringSyntaxChecker>();
+}
+
+bool ento::shouldRegisterCStringSyntaxChecker(const LangOptions &LO) {
+  return true;
+}