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xen/blkfront: avoid NULL blkfront_info dereference on device removal 

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>
This commit is contained in:
Vasilis Liaskovitis 2018-10-15 15:25:08 +02:00 committed by Jens Axboe
parent 3acbd2de6b
commit f92898e7f3
1 changed files with 3 additions and 0 deletions
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3
drivers/block/xen-blkfront.c
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@ -2493,6 +2493,9 @@ 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);