linux-kernel - [PATCH] xen-blkfront: fix kernel panic with blkfront

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Date:   Thu,  8 Nov 2018 16:58:28 -0800
From:   Manjunath Patil <manjunath.b.patil@...cle.com>
To:     boris.ostrovsky@...cle.com, jgross@...e.com,
        konrad.wilk@...cle.com, roger.pau@...rix.com
Cc:     axboe@...nel.dk, xen-devel@...ts.xenproject.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH] xen-blkfront: fix kernel panic with blkfront_remove()

If a hot-attaching device fails inside domU[ex:negotiate_mq() returns
with ENOMEM] we clear the blkfront_info struct in talk_to_blkback()

When we try to detach the device, blkfront_remove() tries to access
blkfront_info leading to kernel panic.

Typical call stack involving panic -
 #10 page_fault at ffffffff816f25df
     [exception RIP: blkif_free+46]
 #11 blkfront_remove at ffffffffa004de47 [xen_blkfront]
 #12 xenbus_dev_remove at ffffffff813faa4c
 #13 __device_release_driver at ffffffff814769aa
 #14 device_release_driver at ffffffff81476a63
 #15 bus_remove_device at ffffffff814762eb
 #16 device_del at ffffffff81472684
 #17 device_unregister at ffffffff814727e2
 #18 xenbus_dev_changed at ffffffff813fa89f
 #19 frontend_changed at ffffffff813fca19
 #20 xenwatch_thread at ffffffff813f88f9
 #21 kthread at ffffffff810a486b
 #22 ret_from_fork at ffffffff816ed2a8

Cc: stable@...r.kernel.org
Signed-off-by: Manjunath Patil <manjunath.b.patil@...cle.com>
---
 drivers/block/xen-blkfront.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index dc8fe25..144cda8 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -2496,6 +2496,9 @@ static int blkfront_remove(struct xenbus_device *xbdev)
 
 	dev_dbg(&xbdev->dev, "%s removed", xbdev->nodename);
 
+	if(!info)
+		return 0;
+
 	blkif_free(info, 0);
 
 	mutex_lock(&info->mutex);
-- 
1.7.1