get_timer: don't use uninitialized memory

get_timer with reset=1 is called both to initialize a
timer object and to reset an already-initialized object. In an
initial call, the content of the data structure is indeterminate, so
the code should not read from it. This could crash if signed overflows
trap, for example.

As a consequence, on reset, we can't return the previously elapsed
time as was previously done on Windows. Return 0 as was done on Unix.

ChangeLog

@@ -44,6 +44,7 @@ Bugfix
    * Fix crash when calling mbedtls_ssl_cache_free() twice. Found by
      MilenkoMitrovic, #1104
    * Fix mbedtls_timing_alarm(0) on Unix.
+   * Fix use of uninitialized memory in mbedtls_timing_get_timer when reset=1.
 
 Changes
    * Extend cert_write example program by options to set the CRT version

library/timing.c

@@ -234,22 +234,24 @@ volatile int alarmed = 0;
 
 unsigned long get_timer( struct hr_time *val, int reset )
 {
-    unsigned long delta;
-    LARGE_INTEGER offset, hfreq;
     struct _hr_time *t = (struct _hr_time *) val;
 
-    QueryPerformanceCounter(  &offset );
-    QueryPerformanceFrequency( &hfreq );
-
-    delta = (unsigned long)( ( 1000 *
-        ( offset.QuadPart - t->start.QuadPart ) ) /
-           hfreq.QuadPart );
-
     if( reset )
+    {
         QueryPerformanceCounter( &t->start );
-
+        return( 0 );
+    }
+    else
+    {
+        unsigned long delta;
+        LARGE_INTEGER now, hfreq;
+        QueryPerformanceCounter(  &now );
+        QueryPerformanceFrequency( &hfreq );
+        delta = (unsigned long)( ( now.QuadPart - t->start.QuadPart ) * 1000ul
+                                 / hfreq.QuadPart );
         return( delta );
     }
+}
 
 /* It's OK to use a global because alarm() is supposed to be global anyway */
 static DWORD alarmMs;
@@ -280,24 +282,23 @@ void m_sleep( int milliseconds )
 
 unsigned long get_timer( struct hr_time *val, int reset )
 {
-    unsigned long delta;
-    struct timeval offset;
     struct _hr_time *t = (struct _hr_time *) val;
 
-    gettimeofday( &offset, NULL );
-
     if( reset )
     {
-        t->start.tv_sec  = offset.tv_sec;
-        t->start.tv_usec = offset.tv_usec;
+        gettimeofday( &t->start, NULL );
         return( 0 );
     }
-
-    delta = ( offset.tv_sec  - t->start.tv_sec  ) * 1000
-          + ( offset.tv_usec - t->start.tv_usec ) / 1000;
-
+    else
+    {
+        unsigned long delta;
+        struct timeval now;
+        gettimeofday( &now, NULL );
+        delta = ( now.tv_sec  - t->start.tv_sec  ) * 1000ul
+              + ( now.tv_usec - t->start.tv_usec ) / 1000;
         return( delta );
     }
+}
 
 #if defined(INTEGRITY)
 void m_sleep( int milliseconds )