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Date:      Sun, 18 Dec 2016 14:31:11 +0000 (UTC)
From:      Dimitry Andric <dim@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-9@freebsd.org
Subject:   svn commit: r310228 - in stable: 10/sys/dev/xen/blkfront 11/sys/dev/xen/blkfront 9/sys/dev/xen/blkfront
Message-ID:  <201612181431.uBIEVBgn007828@repo.freebsd.org>
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Author: dim
Date: Sun Dec 18 14:31:11 2016
New Revision: 310228
URL: https://svnweb.freebsd.org/changeset/base/310228

Log:
  MFC r310013 (by cperciva):
  
  Check that blkfront devices have a non-zero number of sectors and a
  non-zero sector size.  Such a device would be a virtual disk of zero
  bytes; clearly not useful, and not something we should try to attach.
  
  As a fortuitous side effect, checking that these values are non-zero
  here results in them not *becoming* zero later on the function.  This
  odd behaviour began with r309124 (clang 3.9.0) but is challenging to
  debug; making any changes to this function whatsoever seems to affect
  the llvm optimizer behaviour enough to make the unexpected zeroing of
  the sector_size variable cease.
  
  PR:		215209
  Security:	The potential for variables to unexpectedly become zero
  		has worrying consequences for security in general, but
  		not so much in this particular context.
  
  MFC r310086:
  
  In xbd_connect(), use correct scanf conversion specifiers for the
  feature_barrier and feature_flush variables.  Otherwise, adjacent
  variables on the stack, such as sector_size, may be overwritten, with
  disastrous results.
  
  Note that I did not see a good reason to revert the addition of zero
  checks introduced in r310013.  Better safe than sorry.
  
  PR:		215209
  Tested by:	royger

Modified:
  stable/9/sys/dev/xen/blkfront/blkfront.c
Directory Properties:
  stable/9/   (props changed)
  stable/9/sys/   (props changed)

Changes in other areas also in this revision:
Modified:
  stable/10/sys/dev/xen/blkfront/blkfront.c
  stable/11/sys/dev/xen/blkfront/blkfront.c
Directory Properties:
  stable/10/   (props changed)
  stable/11/   (props changed)

Modified: stable/9/sys/dev/xen/blkfront/blkfront.c
==============================================================================
--- stable/9/sys/dev/xen/blkfront/blkfront.c	Sun Dec 18 14:10:24 2016	(r310227)
+++ stable/9/sys/dev/xen/blkfront/blkfront.c	Sun Dec 18 14:31:11 2016	(r310228)
@@ -933,8 +933,16 @@ blkfront_connect(struct xb_softc *sc)
 		    xenbus_get_otherend_path(dev));
 		return;
 	}
+	if ((sectors == 0) || (sector_size == 0)) {
+		xenbus_dev_fatal(dev, 0,
+		    "invalid parameters from %s:"
+		    " sectors = %lu, sector_size = %lu",
+		    xenbus_get_otherend_path(dev),
+		    sectors, sector_size);
+		return;
+	}
 	err = xs_gather(XST_NIL, xenbus_get_otherend_path(dev),
-			"feature-barrier", "%lu", &feature_barrier,
+			"feature-barrier", "%d", &feature_barrier,
 			NULL);
 	if (!err || feature_barrier)
 		sc->xb_flags |= XB_BARRIER;

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