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From: Alan Cox <alc@FreeBSD.org>
Date: Wed, 7 Dec 2011 07:03:14 +0000 (UTC)
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Subject: svn commit: r228317 - head/sys/kern
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Author: alc
Date: Wed Dec  7 07:03:14 2011
New Revision: 228317
URL: http://svn.freebsd.org/changeset/base/228317

Log:
  Eliminate the possibility of 32-bit arithmetic overflow in the calculation
  of vm_kmem_size that may occur if the system administrator has specified a
  vm.vm_kmem_size tunable value that exceeds the hard cap.
  
  PR:		162741
  Submitted by:	Adam McDougall
  Reviewed by:	bde@
  MFC after:	3 weeks

Modified:
  head/sys/kern/kern_malloc.c

Modified: head/sys/kern/kern_malloc.c
==============================================================================
--- head/sys/kern/kern_malloc.c	Wed Dec  7 00:22:34 2011	(r228316)
+++ head/sys/kern/kern_malloc.c	Wed Dec  7 07:03:14 2011	(r228317)
@@ -740,11 +740,11 @@ kmeminit(void *dummy)
 	/*
 	 * Limit kmem virtual size to twice the physical memory.
 	 * This allows for kmem map sparseness, but limits the size
-	 * to something sane. Be careful to not overflow the 32bit
-	 * ints while doing the check.
+	 * to something sane.  Be careful to not overflow the 32bit
+	 * ints while doing the check or the adjustment.
 	 */
-	if (((vm_kmem_size / 2) / PAGE_SIZE) > cnt.v_page_count)
-		vm_kmem_size = 2 * cnt.v_page_count * PAGE_SIZE;
+	if (vm_kmem_size / 2 / PAGE_SIZE > mem_size)
+		vm_kmem_size = 2 * mem_size * PAGE_SIZE;
 
 #ifdef DEBUG_MEMGUARD
 	tmp = memguard_fudge(vm_kmem_size, vm_kmem_size_max);