[PATCH 4.14 118/222] xen/blkfront: avoid NULL blkfront_info dereference on device removal

Greg Kroah-Hartman
2018-11-11T22:59:50Z

From: Vasilis Liaskovitis <vliaskovitis@suse.com>

commit f92898e7f32e3533bfd95be174044bc349d416ca upstream.

If a block device is hot-added when we are out of grants,
gnttab_grant_foreign_access fails with -ENOSPC (log message "28
granting access to ring page") in this code path:

talk_to_blkback ->
setup_blkring ->
xenbus_grant_ring ->
gnttab_grant_foreign_access

and the failing path in talk_to_blkback sets the driver_data to NULL:

destroy_blkring:
blkif_free(info, 0);

mutex_lock(&blkfront_mutex);
free_info(info);
mutex_unlock(&blkfront_mutex);

dev_set_drvdata(&dev->dev, NULL);

This results in a NULL pointer BUG when blkfront_remove and blkif_free
try to access the failing device's NULL struct blkfront_info.

Cc: stable@vger.kernel.org # 4.5 and later
Signed-off-by: Vasilis Liaskovitis <vliaskovitis@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/xen-blkfront.c | 3 +++
1 file changed, 3 insertions(+)

--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -2471,6 +2471,9 @@ static int blkfront_remove(struct xenbus

dev_dbg(&xbdev->dev, "%s removed", xbdev->nodename);

+ if (!info)
+ return 0;
+
blkif_free(info, 0);

mutex_lock(&info->mutex);