null_blk: fix validation of block size

JIRA: https://issues.redhat.com/browse/RHEL-51322
CVE: CVE-2024-41077

commit c462ecd
Author: Andreas Hindborg <a.hindborg@samsung.com>
Date:   Mon Jun 3 21:26:45 2024 +0200

    null_blk: fix validation of block size

    Block size should be between 512 and PAGE_SIZE and be a power of 2. The current
    check does not validate this, so update the check.

    Without this patch, null_blk would Oops due to a null pointer deref when
    loaded with bs=1536 [1].

    Link: https://lore.kernel.org/all/87wmn8mocd.fsf@metaspace.dk/

    Signed-off-by: Andreas Hindborg <a.hindborg@samsung.com>
    Reviewed-by: Ming Lei <ming.lei@redhat.com>
    Link: https://lore.kernel.org/r/20240603192645.977968-1-nmi@metaspace.dk
    [axboe: remove unnecessary braces and != 0 check]
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

drivers/block/null_blk/main.c

@@ -2049,8 +2049,8 @@ static int null_validate_conf(struct nullb_device *dev)
 		return -EINVAL;
 	}
 
-	dev->blocksize = round_down(dev->blocksize, 512);
-	dev->blocksize = clamp_t(unsigned int, dev->blocksize, 512, 4096);
+	if (blk_validate_block_size(dev->blocksize))
+		return -EINVAL;
 
 	if (dev->queue_mode == NULL_Q_MQ && dev->use_per_node_hctx) {
 		if (dev->submit_queues != nr_online_nodes)