[PATCH 4/4] zloop: check that the zone backing file support ->{read,write}_iter

[Christoph Hellwig <hch@lst.de>]

I/O to backing files requires support for iter based read/write, so check
for that upfront instead of dereferencing a NULL pointer later.

Fixes: eb0570c7df23 ("block: new zoned loop block device driver")
Reported-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zloop.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/block/zloop.c b/drivers/block/zloop.c
index f0aca9d43851..65634a39b0bf 100644
--- a/drivers/block/zloop.c
+++ b/drivers/block/zloop.c
@@ -1132,6 +1132,11 @@ static int zloop_init_zone(struct zloop_device *zlo, struct zloop_options *opts,
 		return PTR_ERR(zone->file);
 	}
 
+	if (!zone->file->f_op->read_iter || !zone->file->f_op->write_iter) {
+		ret = -EINVAL;
+		goto out_fput;
+	}
+
 	if (zlo->block_size) {
 		ret = zloop_get_block_size(zlo, zone);
 		if (ret)
-- 
2.53.0