infinite loop in win32 randomness gatherer

[Ian Goldberg]

I'm using libgcrypt 1.2.1 under win32 (mingw cross-compile).

Under some circumstances, I found that libgcrypt would go into an
infinite (well, to the limits of my patience) loop.  A whole lot of
fprintfs later, I tracked down the problem.

slow_gatherer_windows95 walks the heap table and adds everything in it
to the randomness pool.  What seems to be happening is that the act of
adding things to the pool, is changing the table, and you end up with an
infinite loop if that change is to add an item _after_ the place you
currently are in the scan.

Here's a patch that just cuts your losses by adding a maximum of 500
heap entries.  It seems to work Much Better Now (tm).  ;-)

Thanks,

   - Ian

--- rndw32.c.orig	2003-12-11 10:46:12.000000000 -0500
+++ rndw32.c	2005-01-18 09:45:26.000000000 -0500
@@ -238,6 +238,8 @@
 
     /* Walk through the local heap */
     {	HEAPLIST32 hl32;
+	DWORD dwHeapsAdded = 0;
+	const DWORD maxHeapsToAdd = 500;
 	hl32.dwSize = sizeof (HEAPLIST32);
 	if (pHeap32ListFirst (hSnapshot, &hl32)) {
 	    if ( debug_me )
@@ -254,12 +256,16 @@
 		if (pHeap32First (&he32, hl32.th32ProcessID, hl32.th32HeapID)){
 		    do {
 			(*add) ( &he32, sizeof (he32), requester );
+			if (++dwHeapsAdded == maxHeapsToAdd) {
+			    goto doneheap;
+			}
 		    } while (pHeap32Next (&he32));
 		}
 	    } while (pHeap32ListNext (hSnapshot, &hl32));
 	}
     }
 
+doneheap:
 
     /* Walk through all processes */
     {	PROCESSENTRY32 pe32;