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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Thu, 8 Nov 2012 03:17:41 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r242744 - head/sys/dev/md
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Author: kib
Date: Thu Nov  8 03:17:41 2012
New Revision: 242744
URL: http://svnweb.freebsd.org/changeset/base/242744

Log:
  Zero the newly allocated md(4) swap-backed page to prevent random
  kernel memory leakage to userspace. For the typical use, when a
  filesystem put on the md disk, the change only results in CPU and
  memory bandwidth spent to zero the page, since filsystems make sure
  that user never see unwritten content.  But if md disk is used as raw
  device by userspace, the garbage is exposed.
  
  Reported by:	Paul Schenkeveld <freebsd@psconsult.nl>
  MFC after:	2 weeks

Modified:
  head/sys/dev/md/md.c

Modified: head/sys/dev/md/md.c
==============================================================================
--- head/sys/dev/md/md.c	Thu Nov  8 02:55:30 2012	(r242743)
+++ head/sys/dev/md/md.c	Thu Nov  8 03:17:41 2012	(r242744)
@@ -677,6 +677,15 @@ mdstart_swap(struct md_s *sc, struct bio
 				sched_unpin();
 				vm_page_wakeup(m);
 				break;
+			} else if (rv == VM_PAGER_FAIL) {
+				/*
+				 * Pager does not have the page.  Zero
+				 * the allocated page, and mark it as
+				 * valid. Do not set dirty, the page
+				 * can be recreated if thrown out.
+				 */
+				bzero((void *)sf_buf_kva(sf), PAGE_SIZE);
+				m->valid = VM_PAGE_BITS_ALL;
 			}
 			bcopy((void *)(sf_buf_kva(sf) + offs), p, len);
 			cpu_flush_dcache(p, len);