block: disable entropy contributions for nonrot devices
Clear QUEUE_FLAG_ADD_RANDOM in all block drivers that set
QUEUE_FLAG_NONROT.
Historically, all block devices have automatically made entropy
contributions. But as previously stated in commit e2e1a148 ("block: add
sysfs knob for turning off disk entropy contributions"):
- On SSD disks, the completion times aren't as random as they
are for rotational drives. So it's questionable whether they
should contribute to the random pool in the first place.
- Calling add_disk_randomness() has a lot of overhead.
There are more reliable sources for randomness than non-rotational block
devices. From a security perspective it is better to err on the side of
caution than to allow entropy contributions from unreliable "random"
sources.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index a3b042c..b0d94b6 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -507,6 +507,7 @@
nullb->q->queuedata = nullb;
queue_flag_set_unlocked(QUEUE_FLAG_NONROT, nullb->q);
+ queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, nullb->q);
disk = nullb->disk = alloc_disk_node(1, home_node);
if (!disk)