From: Kris Shannon <kris@shannon.id.au>
Date: Mon, 2 Mar 2009 08:47:37 +0000 (+1100)
Subject: Fix kernel NULL pointer dereference in xen-blkfront
X-Git-Tag: v2.6.29-rc8~68^2~3
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=a1a15ac5f9aeee521c048a88fc1aec848e623de7;p=profile%2Fcommon%2Fkernel-common.git

Fix kernel NULL pointer dereference in xen-blkfront

When booting Xen Dom0 on a pre-release 3.2.1 hypervisor the system Oopses on a
"Unable to handle kernel NULL pointer dereference" in xenwatch.

From the backtrace it looks like backend_changed is calling bdget_disk
with a NULL pointer.  Checking for NULL and returning ENODEV instead
allows the kernel to boot.
---

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index b6c8ce2..8f90508 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -977,6 +977,8 @@ static void backend_changed(struct xenbus_device *dev,
 		break;
 
 	case XenbusStateClosing:
+		if (info->gd == NULL)
+			xenbus_dev_fatal(dev, -ENODEV, "gd is NULL");
 		bd = bdget_disk(info->gd, 0);
 		if (bd == NULL)
 			xenbus_dev_fatal(dev, -ENODEV, "bdget failed");