[clang-tidy] Add check 'bugprone-cast-to-struct'

clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp

@@ -18,6 +18,7 @@
 #include "BranchCloneCheck.h"
 #include "CapturingThisInMemberVariableCheck.h"
 #include "CastingThroughVoidCheck.h"
+#include "CastToStructCheck.h"
 #include "ChainedComparisonCheck.h"
 #include "ComparePointerToMemberVirtualFunctionCheck.h"
 #include "CopyConstructorInitCheck.h"
@@ -125,6 +126,7 @@ class BugproneModule : public ClangTidyModule {
         "bugprone-capturing-this-in-member-variable");
     CheckFactories.registerCheck<CastingThroughVoidCheck>(
         "bugprone-casting-through-void");
+    CheckFactories.registerCheck<CastToStructCheck>("bugprone-cast-to-struct");
     CheckFactories.registerCheck<ChainedComparisonCheck>(
         "bugprone-chained-comparison");
     CheckFactories.registerCheck<ComparePointerToMemberVirtualFunctionCheck>(

clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt

@@ -14,6 +14,7 @@ add_clang_library(clangTidyBugproneModule STATIC
   BugproneTidyModule.cpp
   CapturingThisInMemberVariableCheck.cpp
   CastingThroughVoidCheck.cpp
+  CastToStructCheck.cpp
   ChainedComparisonCheck.cpp
   ComparePointerToMemberVirtualFunctionCheck.cpp
   CopyConstructorInitCheck.cpp

clang-tools-extra/clang-tidy/bugprone/CastToStructCheck.cpp

@@ -0,0 +1,82 @@
+//===--- CastToStructCheck.cpp - clang-tidy -------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "CastToStructCheck.h"
+#include "../utils/Matchers.h"
+#include "../utils/OptionsUtils.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+CastToStructCheck::CastToStructCheck(StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      IgnoredCasts(
+          utils::options::parseStringList(Options.get("IgnoredCasts", ""))) {}
+
+void CastToStructCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "IgnoredCasts",
+                utils::options::serializeStringList(IgnoredCasts));
+}
+
+void CastToStructCheck::registerMatchers(MatchFinder *Finder) {
+  auto FromPointee =
+      qualType(hasUnqualifiedDesugaredType(type().bind("FromType")),
+               unless(voidType()),
+               unless(hasDeclaration(recordDecl(isUnion()))))
+          .bind("FromPointee");
+  auto ToPointee =
+      qualType(hasUnqualifiedDesugaredType(
+                   recordType(unless(hasDeclaration(recordDecl(isUnion()))))
+                       .bind("ToType")))
+          .bind("ToPointee");
+  auto FromPtrType = qualType(pointsTo(FromPointee)).bind("FromPtr");
+  auto ToPtrType = qualType(pointsTo(ToPointee)).bind("ToPtr");
+  Finder->addMatcher(cStyleCastExpr(hasSourceExpression(hasType(FromPtrType)),
+                                    hasType(ToPtrType))
+                         .bind("CastExpr"),
+                     this);
+}
+
+void CastToStructCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *const FoundCastExpr =
+      Result.Nodes.getNodeAs<CStyleCastExpr>("CastExpr");
+  const auto *const FromPtr = Result.Nodes.getNodeAs<QualType>("FromPtr");
+  const auto *const ToPtr = Result.Nodes.getNodeAs<QualType>("ToPtr");
+  const auto *const FromPointee =
+      Result.Nodes.getNodeAs<QualType>("FromPointee");
+  const auto *const ToPointee = Result.Nodes.getNodeAs<QualType>("ToPointee");
+  const auto *const FromType = Result.Nodes.getNodeAs<Type>("FromType");
+  const auto *const ToType = Result.Nodes.getNodeAs<RecordType>("ToType");
+
+  if (FromType == ToType)
+    return;
+
+  const std::string FromName = FromPointee->getAsString();
+  const std::string ToName = ToPointee->getAsString();
+  llvm::Regex FromR;
+  llvm::Regex ToR;
+  for (auto [Idx, Str] : llvm::enumerate(IgnoredCasts)) {
+    if (Idx % 2 == 0) {
+      FromR = llvm::Regex(Str);
+    } else {
+      ToR = llvm::Regex(Str);
+      if (FromR.match(FromName) && ToR.match(ToName))
+        return;
+    }
+  }
+
+  diag(FoundCastExpr->getExprLoc(),
+       "casting a %0 pointer to a "
+       "%1 pointer and accessing a field can lead to memory "
+       "access errors or data corruption")
+      << *FromPtr << *ToPtr;
+}
+
+} // namespace clang::tidy::bugprone

clang-tools-extra/clang-tidy/bugprone/CastToStructCheck.h

@@ -0,0 +1,37 @@
+//===--- CastToStructCheck.h - clang-tidy -----------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_CASTTOSTRUCTCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_CASTTOSTRUCTCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::bugprone {
+
+/// Finds casts from pointers to struct or scalar type to pointers to struct
+/// type.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/bugprone/cast-to-struct.html
+class CastToStructCheck : public ClangTidyCheck {
+public:
+  CastToStructCheck(StringRef Name, ClangTidyContext *Context);
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.C99;
+  }
+
+private:
+  std::vector<llvm::StringRef> IgnoredCasts;
+};
+
+} // namespace clang::tidy::bugprone
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_CASTTOSTRUCTCHECK_H

clang-tools-extra/docs/ReleaseNotes.rst

@@ -112,6 +112,11 @@ Improvements to clang-tidy
 New checks
 ^^^^^^^^^^
 
+- New :doc:`bugprone-cast-to-struct
+  <clang-tidy/checks/bugprone/cast-to-struct>` check.
+
+  Finds casts from pointers to struct or scalar type to pointers to struct type.
+
 - New :doc:`bugprone-invalid-enum-default-initialization
   <clang-tidy/checks/bugprone/invalid-enum-default-initialization>` check.
 

clang-tools-extra/docs/clang-tidy/checks/bugprone/cast-to-struct.rst

@@ -0,0 +1,60 @@
+.. title:: clang-tidy - bugprone-cast-to-struct
+
+bugprone-cast-to-struct
+=======================
+
+Finds casts from pointers to struct or scalar type to pointers to struct type.
+
+Casts between pointers to different structs can be unsafe because it is possible
+to access uninitialized or undefined data after the cast. Cast from a
+scalar-type pointer (which points often to an array or memory block) to a
+``struct`` type pointer can be unsafe for similar reasons. This check warns at
+pointer casts from any non-struct type to a struct type. No warning is produced
+at cast from type ``void *`` (this is the usual way of allocating memory with
+``malloc``-like functions). In addition, ``union`` types are excluded from the
+check. It is possible to specify additional types to ignore. The check does not
+take into account type compatibility or data layout, only the names of the
+types.
+
+.. code-block:: c
+
+   void test1(char *p) {
+     struct S1 *s;
+     s = (struct S1 *)p; // warn: 'char *' is converted to 'struct S1 *'
+   }
+
+   void test2(struct S1 *p) {
+     struct S2 *s;
+     s = (struct S2 *)p; // warn: 'struct S1 *' is converted to 'struct S2 *'
+   }
+
+   void test3(void) {
+     struct S1 *s;
+     s = (struct S1 *)calloc(1, sizeof(struct S1)); // no warning
+   }
+
+Limitations
+-----------
+
+The check does run only on `C` code.
+
+C-style casts are discouraged in `C++` and should be converted to more type-safe
+casts. The ``reinterpreted_cast`` is used for the most unsafe cases and
+indicates by itself a potentially dangerous operation. Additionally, inheritance
+and dynamic types would make such a check less useful.
+
+Options
+-------
+
+.. option:: IgnoredCasts
+
+   Can contain a semicolon-separated list of type names that specify cast
+   types to ignore. The list should contain pairs of type names in a way that
+   the first type is the "from" type, the second is the "to" type in a cast
+   expression. The types in a pair and the pairs itself are separated by
+   ``;`` characters. For example ``char;Type1;char;Type2`` specifies that the
+   check does not produce warning for casts from ``char *`` to ``Type1 *`` and
+   casts from ``char *`` to ``Type2 *``. The list entries can be regular
+   expressions. The type name in the cast expression is matched without
+   resolution of type aliases like ``typedef``. Default value is empty list.
+   (Casts from ``void *`` are ignored always regardless of this list.)

clang-tools-extra/docs/clang-tidy/checks/list.rst

@@ -85,6 +85,7 @@ Clang-Tidy Checks
    :doc:`bugprone-bool-pointer-implicit-conversion <bugprone/bool-pointer-implicit-conversion>`, "Yes"
    :doc:`bugprone-branch-clone <bugprone/branch-clone>`,
    :doc:`bugprone-capturing-this-in-member-variable <bugprone/capturing-this-in-member-variable>`,
+   :doc:`bugprone-cast-to-struct <bugprone/cast-to-struct>`,
    :doc:`bugprone-casting-through-void <bugprone/casting-through-void>`,
    :doc:`bugprone-chained-comparison <bugprone/chained-comparison>`,
    :doc:`bugprone-compare-pointer-to-member-virtual-function <bugprone/compare-pointer-to-member-virtual-function>`,

clang-tools-extra/test/clang-tidy/checkers/bugprone/cast-to-struct-ignore.c

@@ -0,0 +1,33 @@
+// RUN: %check_clang_tidy %s bugprone-cast-to-struct %t -- \
+// RUN:   -config="{CheckOptions: {bugprone-cast-to-struct.IgnoredCasts: 'char;S1;int;Other*'}}"
+
+struct S1 {
+  int a;
+};
+
+struct S2 {
+  char a;
+};
+
+struct OtherS {
+  int a;
+  int b;
+};
+
+void test1(char *p1, int *p2) {
+  struct S1 *s1;
+  s1 = (struct S1 *)p1;
+  struct S2 *s2;
+  s2 = (struct S2 *)p1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:8: warning: casting a 'char *' pointer to a 'struct S2 *'
+  s2 = (struct S2 *)p2;
+  // CHECK-MESSAGES: :[[@LINE-1]]:8: warning: casting a 'int *' pointer to a 'struct S2 *'
+  struct OtherS *s3;
+  s3 = (struct OtherS *)p2;
+  s3 = (struct OtherS *)p1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:8: warning: casting a 'char *' pointer to a 'struct OtherS *'
+}
+
+struct S2 *test_void_is_always_ignored(void *p) {
+  return (struct S2 *)p;
+}

clang-tools-extra/test/clang-tidy/checkers/bugprone/cast-to-struct.c

@@ -0,0 +1,66 @@
+// RUN: %check_clang_tidy %s bugprone-cast-to-struct %t
+
+struct S1 {
+  int a;
+};
+
+struct S2 {
+  char a;
+};
+
+union U1 {
+  int a;
+  char b;
+};
+
+union U2 {
+  struct S1 a;
+  char b;
+};
+
+typedef struct S1 TyS1;
+typedef struct S1 *TyPS1;
+
+typedef union U1 *TyPU1;
+
+typedef int int_t;
+typedef int * int_ptr_t;
+
+struct S1 *test_simple(char *p) {
+  return (struct S1 *)p;
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: casting a 'char *' pointer to a 'struct S1 *' pointer and accessing a field can lead to memory access errors or data corruption [bugprone-cast-to-struct]
+  struct S1 *s;
+  int i;
+  s = (struct S1 *)&i;
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: casting a 'int *' pointer to a 'struct S1 *' pointer and accessing a field can lead to memory access errors or data corruption [bugprone-cast-to-struct]
+}
+
+struct S1 *test_cast_from_void(void *p) {
+  return (struct S1 *)p;
+}
+
+struct S1 *test_cast_from_struct(struct S2 *p) {
+  return (struct S1 *)p;
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: casting a 'struct S2 *' pointer to a 'struct S1 *' pointer and accessing a field can lead to memory access errors or data corruption [bugprone-cast-to-struct]
+}
+
+TyPS1 test_cast_from_similar(struct S1 *p) {
+  return (TyPS1)p;
+}
+
+void test_typedef(char *p1, int_t *p2, int_ptr_t p3) {
+  TyS1 *a = (TyS1 *)p1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: casting a 'char *' pointer to a 'TyS1 *' (aka 'struct S1 *') pointer and accessing a field can lead to memory access errors or data corruption [bugprone-cast-to-struct]
+  TyPS1 b = (TyPS1)p1;
+  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: casting a 'char *' pointer to a 'TyPS1' (aka 'struct S1 *') pointer and accessing a field can lead to memory access errors or data corruption [bugprone-cast-to-struct]
+  struct S1 *c = (struct S1 *)p2;
+  // CHECK-MESSAGES: :[[@LINE-1]]:18: warning: casting a 'int_t *' (aka 'int *') pointer to a 'struct S1 *' pointer and accessing a field can lead to memory access errors or data corruption [bugprone-cast-to-struct]
+  struct S1 *d = (struct S1 *)p3;
+  // CHECK-MESSAGES: :[[@LINE-1]]:18: warning: casting a 'int_ptr_t' (aka 'int *') pointer to a 'struct S1 *' pointer and accessing a field can lead to memory access errors or data corruption [bugprone-cast-to-struct]
+}
+
+void test_union(char *p1, union U1 *p2, TyPU1 p3) {
+  union U1 *a = (union U1 *)p1;
+  struct S1 *b = (struct S1 *)p2;
+  struct S1 *c = (struct S1 *)p3;
+}