From: Cathy Avery <cathy.avery@oracle.com>
Date: Fri, 2 Oct 2015 13:35:01 +0000 (-0400)
Subject: xen-blkfront: check for null drvdata in blkback_changed (XenbusStateClosing)
X-Git-Tag: v3.16.35~1119
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=51854900c0d808a3e20beccfc03c447182b186ca;p=thirdparty%2Fkernel%2Fstable.git

xen-blkfront: check for null drvdata in blkback_changed (XenbusStateClosing)

commit a54c8f0f2d7df525ff997e2afe71866a1a013064 upstream.

xen-blkfront will crash if the check to talk_to_blkback()
in blkback_changed()(XenbusStateInitWait) returns an error.
The driver data is freed and info is set to NULL. Later during
the close process via talk_to_blkback's call to xenbus_dev_fatal()
the null pointer is passed to and dereference in blkfront_closing.

Signed-off-by: Cathy Avery <cathy.avery@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 2a29cf69cd732..1b683dbc3f88c 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1905,7 +1905,8 @@ static void blkback_changed(struct xenbus_device *dev,
 			break;
 		/* Missed the backend's Closing state -- fallthrough */
 	case XenbusStateClosing:
-		blkfront_closing(info);
+		if (info)
+			blkfront_closing(info);
 		break;
 	}
 }