[PATCH v6 4/7] kernel32: Fix CreateToolhelp32Snapshot on old WoW64.

[Yuxuan Shui]

From: Yuxuan Shui

On old WoW64 PEB->LdrData is NULL, so later ReadProcessMemory(&NULL->InLoadOrderModuleList.Flink)
fails. Don't return failure in this case.
---
 dlls/kernel32/toolhelp.c | 69 ++++++++++++++++++++++------------------
 1 file changed, 38 insertions(+), 31 deletions(-)

diff --git a/dlls/kernel32/toolhelp.c b/dlls/kernel32/toolhelp.c
index 5e1ec84d100..282f6828f86 100644
--- a/dlls/kernel32/toolhelp.c
+++ b/dlls/kernel32/toolhelp.c
@@ -92,42 +92,49 @@ static BOOL fetch_module( DWORD process, DWORD flags, LDR_DATA_TABLE_ENTRY **ldr
     if (set_ntstatus( NtQueryInformationProcess( hProcess, ProcessBasicInformation,
                                                  &pbi, sizeof(pbi), NULL )))
     {
-        if (ReadProcessMemory( hProcess, &pbi.PebBaseAddress->LdrData,
-                               &pLdrData, sizeof(pLdrData), NULL ) &&
-            ReadProcessMemory( hProcess,
-                               &pLdrData->InLoadOrderModuleList.Flink,
-                               &curr, sizeof(curr), NULL ))
+        if (!ReadProcessMemory( hProcess, &pbi.PebBaseAddress->LdrData,
+                               &pLdrData, sizeof(pLdrData), NULL ))
+            goto out;
+        if (!pLdrData)
         {
-            head = &pLdrData->InLoadOrderModuleList;
-
-            while (curr != head)
-            {
-                if (!*num)
-                    *ldr_mod = HeapAlloc( GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(LDR_DATA_TABLE_ENTRY) );
-                else
-                    *ldr_mod = HeapReAlloc( GetProcessHeap(), HEAP_ZERO_MEMORY, *ldr_mod,
-                                            (*num + 1) * sizeof(LDR_DATA_TABLE_ENTRY) );
-                if (!*ldr_mod) break;
-                if (!ReadProcessMemory( hProcess,
-                                        CONTAINING_RECORD(curr, LDR_DATA_TABLE_ENTRY,
-                                                          InLoadOrderLinks),
-                                        &(*ldr_mod)[*num],
-                                        sizeof(LDR_DATA_TABLE_ENTRY), NULL))
-                    break;
-                curr = (*ldr_mod)[*num].InLoadOrderLinks.Flink;
-                /* if we cannot fetch the strings, then just ignore this LDR_DATA_TABLE_ENTRY
-                 * and continue loading the other ones in the list
-                 */
-                if (!fetch_string( hProcess, &(*ldr_mod)[*num].BaseDllName )) continue;
-                if (fetch_string( hProcess, &(*ldr_mod)[*num].FullDllName ))
-                    (*num)++;
-                else
-                    HeapFree( GetProcessHeap(), 0, (*ldr_mod)[*num].BaseDllName.Buffer );
-            }
+            /* This happens on "old" wow64. Don't fail, just return an empty modules list. */
             ret = TRUE;
+            goto out;
+        }
+        if (!ReadProcessMemory( hProcess, &pLdrData->InLoadOrderModuleList.Flink,
+                               &curr, sizeof(curr), NULL ))
+            goto out;
+
+        head = &pLdrData->InLoadOrderModuleList;
+
+        while (curr != head)
+        {
+            if (!*num)
+                *ldr_mod = HeapAlloc( GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(LDR_DATA_TABLE_ENTRY) );
+            else
+                *ldr_mod = HeapReAlloc( GetProcessHeap(), HEAP_ZERO_MEMORY, *ldr_mod,
+                                        (*num + 1) * sizeof(LDR_DATA_TABLE_ENTRY) );
+            if (!*ldr_mod) break;
+            if (!ReadProcessMemory( hProcess,
+                                    CONTAINING_RECORD(curr, LDR_DATA_TABLE_ENTRY,
+                                                      InLoadOrderLinks),
+                                    &(*ldr_mod)[*num],
+                                    sizeof(LDR_DATA_TABLE_ENTRY), NULL))
+                break;
+            curr = (*ldr_mod)[*num].InLoadOrderLinks.Flink;
+            /* if we cannot fetch the strings, then just ignore this LDR_DATA_TABLE_ENTRY
+             * and continue loading the other ones in the list
+             */
+            if (!fetch_string( hProcess, &(*ldr_mod)[*num].BaseDllName )) continue;
+            if (fetch_string( hProcess, &(*ldr_mod)[*num].FullDllName ))
+                (*num)++;
+            else
+                HeapFree( GetProcessHeap(), 0, (*ldr_mod)[*num].BaseDllName.Buffer );
         }
+        ret = TRUE;
     }

+out:
     if (process) CloseHandle( hProcess );
     return ret;
 }