[PATCH] xen-blkfront: fix kernel panic with blkfront_remove()

Manjunath Patil
2018-11-09T00:57:40Z

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@vger.kernel.org
Signed-off-by: Manjunath Patil <manjunath.b.patil@oracle.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