[ofw] Division by zero in etc/user/gtod.c

[Schmitt, Hubert]

Hello everybody,
 
There is a potential bug (division by zero) in the gettimeofday()
function which should be fixed with suggested patch below.
The point is to move the 'QueryCounter = 1' behind calling
QueryPerformanceFrequency().
Otherwise another thread (within current process) could pre-empt the
current one right after 'QueryCounter = 1',
and thus would work with an uninitialized (i.e. zero) Frequency
variable.
 
Thanks,
Hubert.
 
 
Index: gtod.c
===================================================================
--- gtod.c (revision 3414)
+++ gtod.c (working copy)
@@ -62,6 +62,9 @@
 int gettimeofday(struct timeval *ptv, void *ignored)
 {
  static int QueryCounter = 2;
+ static LARGE_INTEGER Frequency = {10000000,0}; /* prevent division by
0 */
+ static LARGE_INTEGER Offset; /* counter offset for right time*/
+ static LARGE_INTEGER LastCounter;
  FILETIME CurrentTime;
  UNREFERENCED_PARAMETER(ignored);     
 
@@ -69,9 +72,6 @@
 
  if(QueryCounter)
  {
-  static LARGE_INTEGER Frequency;
-  static LARGE_INTEGER Offset; /* counter offset for right time*/
-  static LARGE_INTEGER LastCounter;
   LARGE_INTEGER Time;
   LARGE_INTEGER Counter;
  
@@ -80,13 +80,15 @@
  
   if(QueryCounter == 2)
   {
-   QueryCounter = 1;
-   if(!QueryPerformanceFrequency(&Frequency))
+   if(QueryPerformanceFrequency(&Frequency))
    {
+    QueryCounter = 1; // But now the Frequency is valid!
+   }
+   else
+   {
     QueryCounter = 0;
     Frequency.QuadPart = 10000000; /* prevent division by 0 */
    }
- 
    /* get time as a large integer */
    Counter.HighPart &= 0x7FL; /* Clear high bits to prevent overflow */
    Offset.LowPart = CurrentTime.dwLowDateTime;



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