[PATCH 3.13.y-ckt 67/96] xen-blkfront: check for null drvdata in blkback_changed (XenbusStateClosing)

From: Kamal Mostafa
Date: Fri Nov 13 2015 - 17:02:10 EST

3.13.11-ckt30 -stable review patch. If anyone has any objections, please let me know.


From: Cathy Avery <cathy.avery@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
drivers/block/xen-blkfront.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index fdee753..0035645e 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1917,7 +1917,8 @@ static void blkback_changed(struct xenbus_device *dev,
/* Missed the backend's Closing state -- fallthrough */
case XenbusStateClosing:
- blkfront_closing(info);
+ if (info)
+ blkfront_closing(info);

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