From c671041720347c9deb35b1165ee6b6bb88abf07a Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron@aaronballman.com>
Date: Thu, 12 May 2022 13:19:26 -0400
Subject: [PATCH] Check for resource exhaustion when recursively parsing
 declarators

With sufficiently tortured code, it's possible to cause a stack
overflow when parsing declarators. Thus, we now check for resource
exhaustion when recursively parsing declarators so that we can at least
warn the user we're about to crash before we actually crash.

Fixes #51642

Differential Revision: https://reviews.llvm.org/D124915
---
 clang/docs/ReleaseNotes.rst   |  4 +++-
 clang/lib/Parse/ParseDecl.cpp | 15 ++++++++++-----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e7dd0d1d6e91..7c25456adb25 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -222,7 +222,9 @@ Improvements to Clang's diagnostics
   on such language mode, ``-Wpre-c2x-compat`` and ``-Wpre-c++2b-compat``
   diagnostic flags report a compatibility issue.
   Fixes `Issue 55306 <https://github.com/llvm/llvm-project/issues/55306>`_.
-
+- Clang now checks for stack resource exhaustion when recursively parsing
+  declarators in order to give a diagnostic before we run out of stack space.
+  This fixes `Issue 51642 <https://github.com/llvm/llvm-project/issues/51642>`_.
 
 Non-comprehensive list of changes in this release
 -------------------------------------------------
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 89e13cf5c90f..306644fc4b21 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -5765,11 +5765,12 @@ void Parser::ParseTypeQualifierListOpt(
 }
 
 /// ParseDeclarator - Parse and verify a newly-initialized declarator.
-///
 void Parser::ParseDeclarator(Declarator &D) {
   /// This implements the 'declarator' production in the C grammar, then checks
   /// for well-formedness and issues diagnostics.
-  ParseDeclaratorInternal(D, &Parser::ParseDirectDeclarator);
+  Actions.runWithSufficientStackSpace(D.getBeginLoc(), [&] {
+    ParseDeclaratorInternal(D, &Parser::ParseDirectDeclarator);
+  });
 }
 
 static bool isPtrOperatorToken(tok::TokenKind Kind, const LangOptions &Lang,
@@ -5880,7 +5881,9 @@ void Parser::ParseDeclaratorInternal(Declarator &D,
       D.ExtendWithDeclSpec(DS);
 
       // Recurse to parse whatever is left.
-      ParseDeclaratorInternal(D, DirectDeclParser);
+      Actions.runWithSufficientStackSpace(D.getBeginLoc(), [&] {
+        ParseDeclaratorInternal(D, DirectDeclParser);
+      });
 
       // Sema will have to catch (syntactically invalid) pointers into global
       // scope. It has to catch pointers into namespace scope anyway.
@@ -5929,7 +5932,8 @@ void Parser::ParseDeclaratorInternal(Declarator &D,
     D.ExtendWithDeclSpec(DS);
 
     // Recursively parse the declarator.
-    ParseDeclaratorInternal(D, DirectDeclParser);
+    Actions.runWithSufficientStackSpace(
+        D.getBeginLoc(), [&] { ParseDeclaratorInternal(D, DirectDeclParser); });
     if (Kind == tok::star)
       // Remember that we parsed a pointer type, and remember the type-quals.
       D.AddTypeInfo(DeclaratorChunk::getPointer(
@@ -5974,7 +5978,8 @@ void Parser::ParseDeclaratorInternal(Declarator &D,
     }
 
     // Recursively parse the declarator.
-    ParseDeclaratorInternal(D, DirectDeclParser);
+    Actions.runWithSufficientStackSpace(
+        D.getBeginLoc(), [&] { ParseDeclaratorInternal(D, DirectDeclParser); });
 
     if (D.getNumTypeObjects() > 0) {
       // C++ [dcl.ref]p4: There shall be no references to references.