[clang] Fix null-deref thanks to an attribute on a global declarator chunk (PR #83611)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Erich Keane (erichkeane)

<details>
<summary>Changes</summary>

This was reported (sort of) in a PR: #<!-- -->77703. The problem is that a declarator 'owns' an attributes allocation via an `AttributePool`. However, this example tries to copy a DeclaratorChunk from one Declarator to another, so when the temporary Declarator goes out of scope, it deletes the attribute it has tried to pass on via the chunk.

This patch ensures that we copy the 'ownership' of the attribute correctly, and adds an assert to catch any other casess where this happens.

---
Full diff: https://github.com/llvm/llvm-project/pull/83611.diff


6 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+4-1) 
- (modified) clang/include/clang/Sema/DeclSpec.h (+16) 
- (modified) clang/include/clang/Sema/ParsedAttr.h (+5) 
- (modified) clang/lib/Parse/ParseDecl.cpp (+1-1) 
- (modified) clang/lib/Sema/ParsedAttr.cpp (+6) 
- (added) clang/test/Parser/cxx-declarator-attribute-crash.cpp (+8) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 1286263700963c..3476342ef6f6e4 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -306,7 +306,10 @@ Bug Fixes to C++ Support
   instead of only on class, alias, and variable templates, as last updated by
   CWG2032.
   Fixes (`#83461 <https://github.com/llvm/llvm-project/issues/83461>`_)
-
+- Fixed an issue where an attribute on a declarator would cause the attribute to
+  be destructed prematurely. This fixes a pair of Chromium that were brought to
+  our attention by an attempt to fix in
+  `#77703 <https://github.com/llvm/llvm-project/pull/77703>`_.
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/Sema/DeclSpec.h b/clang/include/clang/Sema/DeclSpec.h
index 316e8071169a3a..a176159707486c 100644
--- a/clang/include/clang/Sema/DeclSpec.h
+++ b/clang/include/clang/Sema/DeclSpec.h
@@ -2359,11 +2359,27 @@ class Declarator {
       SetRangeEnd(EndLoc);
   }
 
+  /// AddTypeInfo - Add a chunk to this declarator. Also extend the range to
+  /// EndLoc, which should be the last token of the chunk. This overload is for
+  /// copying a 'chunk' from another declarator, so it takes the pool that the
+  /// other Declarator owns so that it can 'take' the attributes from it.
+  void AddTypeInfo(const DeclaratorChunk &TI, AttributePool &OtherPool,
+                   SourceLocation EndLoc) {
+    DeclTypeInfo.push_back(TI);
+    getAttributePool().takeFrom(DeclTypeInfo.back().getAttrs(), OtherPool);
+
+    if (!EndLoc.isInvalid())
+      SetRangeEnd(EndLoc);
+  }
+
   /// AddTypeInfo - Add a chunk to this declarator. Also extend the range to
   /// EndLoc, which should be the last token of the chunk.
   void AddTypeInfo(const DeclaratorChunk &TI, SourceLocation EndLoc) {
     DeclTypeInfo.push_back(TI);
 
+    assert(TI.AttrList.empty() &&
+           "Cannot add a declarator chunk with attributes with this overload");
+
     if (!EndLoc.isInvalid())
       SetRangeEnd(EndLoc);
   }
diff --git a/clang/include/clang/Sema/ParsedAttr.h b/clang/include/clang/Sema/ParsedAttr.h
index 8c3ba39031aad8..53cc76da34df27 100644
--- a/clang/include/clang/Sema/ParsedAttr.h
+++ b/clang/include/clang/Sema/ParsedAttr.h
@@ -680,6 +680,7 @@ class AttributeFactory {
   ~AttributeFactory();
 };
 
+class ParsedAttributesView;
 class AttributePool {
   friend class AttributeFactory;
   friend class ParsedAttributes;
@@ -734,6 +735,9 @@ class AttributePool {
     pool.Attrs.clear();
   }
 
+  /// Take a list of attributes from another pool and add them to this pool.
+  void takeFrom(ParsedAttributesView &List, AttributePool &Pool);
+
   ParsedAttr *create(IdentifierInfo *attrName, SourceRange attrRange,
                      IdentifierInfo *scopeName, SourceLocation scopeLoc,
                      ArgsUnion *args, unsigned numArgs, ParsedAttr::Form form,
@@ -816,6 +820,7 @@ class AttributePool {
 };
 
 class ParsedAttributesView {
+  friend class AttributePool;
   using VecTy = llvm::SmallVector<ParsedAttr *>;
   using SizeType = decltype(std::declval<VecTy>().size());
 
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index edfab11c37cf0f..ccbfea6a66fba7 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -7928,7 +7928,7 @@ void Parser::ParseMisplacedBracketDeclarator(Declarator &D) {
   // Adding back the bracket info to the end of the Declarator.
   for (unsigned i = 0, e = TempDeclarator.getNumTypeObjects(); i < e; ++i) {
     const DeclaratorChunk &Chunk = TempDeclarator.getTypeObject(i);
-    D.AddTypeInfo(Chunk, SourceLocation());
+    D.AddTypeInfo(Chunk, TempDeclarator.getAttributePool(), SourceLocation());
   }
 
   // The missing identifier would have been diagnosed in ParseDirectDeclarator.
diff --git a/clang/lib/Sema/ParsedAttr.cpp b/clang/lib/Sema/ParsedAttr.cpp
index 06c213267c7ef5..978d4e7bf4d392 100644
--- a/clang/lib/Sema/ParsedAttr.cpp
+++ b/clang/lib/Sema/ParsedAttr.cpp
@@ -100,6 +100,12 @@ void AttributePool::takePool(AttributePool &pool) {
   pool.Attrs.clear();
 }
 
+void AttributePool::takeFrom(ParsedAttributesView &List, AttributePool &Pool) {
+    assert(&Pool != this && "AttributePool can't take attributes from itself");
+    llvm::for_each(List.AttrList, [&Pool](ParsedAttr *A) { Pool.remove(A); });
+    Attrs.insert(Attrs.end(), List.AttrList.begin(), List.AttrList.end());
+}
+
 namespace {
 
 #include "clang/Sema/AttrParsedAttrImpl.inc"
diff --git a/clang/test/Parser/cxx-declarator-attribute-crash.cpp b/clang/test/Parser/cxx-declarator-attribute-crash.cpp
new file mode 100644
index 00000000000000..3b989a659db569
--- /dev/null
+++ b/clang/test/Parser/cxx-declarator-attribute-crash.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+// expected-error at +5{{brackets are not allowed here}}
+// expected-error at +4{{a type specifier is required for all declarations}}
+// expected-warning at +3{{unknown attribute 'h' ignored}}
+// expected-error at +2{{definition of variable with array type}}
+// expected-error at +1{{expected ';'}}
+[][[h]]l

``````````

</details>


https://github.com/llvm/llvm-project/pull/83611