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From: Anthony Liguori <anthony@codemonkey.ws>
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Date: Sun, 29 Mar 2009 01:31:52 +0000
Subject: [Qemu-devel] [6943] check for bs->drv in bdrv_flush (Christoph
	Hellwig)
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Revision: 6943
          http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=6943
Author:   aliguori
Date:     2009-03-29 01:31:51 +0000 (Sun, 29 Mar 2009)
Log Message:
-----------
check for bs->drv in bdrv_flush (Christoph Hellwig)

All the bdrv_ helpers should check for bs->drv being zero as that means
there is no backend image open.  bdrv_flush fails to perform that check
and can thus cause NULL pointer dereferences.

Found using qemu-io.


Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

Modified Paths:
--------------
    trunk/block.c

Modified: trunk/block.c
===================================================================
--- trunk/block.c	2009-03-29 01:31:48 UTC (rev 6942)
+++ trunk/block.c	2009-03-29 01:31:51 UTC (rev 6943)
@@ -1002,6 +1002,8 @@
 
 void bdrv_flush(BlockDriverState *bs)
 {
+    if (!bs->drv)
+        return;
     if (bs->drv->bdrv_flush)
         bs->drv->bdrv_flush(bs);
     if (bs->backing_hd)