https://github.com/gnuaspell/aspell/commit/0718b375425aad8e54e1150313b862e4c6fd324a
https://nvd.nist.gov/vuln/detail/CVE-2019-25051

From 0718b375425aad8e54e1150313b862e4c6fd324a Mon Sep 17 00:00:00 2001
From: Kevin Atkinson <kevina@gnu.org>
Date: Sat, 21 Dec 2019 20:32:47 +0000
Subject: [PATCH] objstack: assert that the alloc size will fit within a chunk
 to prevent a buffer overflow

Bug found using OSS-Fuze.
---
 common/objstack.hpp | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/common/objstack.hpp b/common/objstack.hpp
index 3997bf7..bd97ccd 100644
--- a/common/objstack.hpp
+++ b/common/objstack.hpp
@@ -5,6 +5,7 @@
 #include "parm_string.hpp"
 #include <stdlib.h>
 #include <assert.h>
+#include <stddef.h>
 
 namespace acommon {
 
@@ -26,6 +27,12 @@ class ObjStack
   byte * temp_end;
   void setup_chunk();
   void new_chunk();
+  bool will_overflow(size_t sz) const {
+    return offsetof(Node,data) + sz > chunk_size;
+  }
+  void check_size(size_t sz) {
+    assert(!will_overflow(sz));
+  }
 
   ObjStack(const ObjStack &);
   void operator=(const ObjStack &);
@@ -56,7 +63,7 @@ class ObjStack
   void * alloc_bottom(size_t size)  {
     byte * tmp = bottom;
     bottom += size;
-    if (bottom > top) {new_chunk(); tmp = bottom; bottom += size;}
+    if (bottom > top) {check_size(size); new_chunk(); tmp = bottom; bottom += size;}
     return tmp;
   }
   // This alloc_bottom will insure that the object is aligned based on the
@@ -66,7 +73,7 @@ class ObjStack
     align_bottom(align);
     byte * tmp = bottom;
     bottom += size;
-    if (bottom > top) {new_chunk(); goto loop;}
+    if (bottom > top) {check_size(size); new_chunk(); goto loop;}
     return tmp;
   }
   char * dup_bottom(ParmString str) {
@@ -79,7 +86,7 @@ class ObjStack
   // always be aligned as such.
   void * alloc_top(size_t size) {
     top -= size;
-    if (top < bottom) {new_chunk(); top -= size;}
+    if (top < bottom) {check_size(size); new_chunk(); top -= size;}
     return top;
   }
   // This alloc_top will insure that the object is aligned based on
@@ -88,7 +95,7 @@ class ObjStack
   {loop:
     top -= size;
     align_top(align);
-    if (top < bottom) {new_chunk(); goto loop;}
+    if (top < bottom) {check_size(size); new_chunk(); goto loop;}
     return top;
   }
   char * dup_top(ParmString str) {
@@ -117,6 +124,7 @@ class ObjStack
   void * alloc_temp(size_t size) {
     temp_end = bottom + size;
     if (temp_end > top) {
+      check_size(size);
       new_chunk();
       temp_end = bottom + size;
     }
@@ -131,6 +139,7 @@ class ObjStack
     } else {
       size_t s = temp_end - bottom;
       byte * p = bottom;
+      check_size(size);
       new_chunk();
       memcpy(bottom, p, s);
       temp_end = bottom + size;
@@ -150,6 +159,7 @@ class ObjStack
     } else {
       size_t s = temp_end - bottom;
       byte * p = bottom;
+      check_size(size);
       new_chunk();
       memcpy(bottom, p, s);
       temp_end = bottom + size;