[PATCH 15/98] zloop: refuse zone files without read/write_iter

[Jens Axboe <axboe@kernel.dk>]

From: Josef Bacik <josef@toxicpanda.com>

zloop_do_rw() calls ->read_iter() and ->write_iter() on the zone files
without checking that they exist. A base_dir on hugetlbfs, or zone files
that are links into procfs, create a device just fine and the first IO
jumps to NULL. Check for both when a zone file is opened, like loop does
for its backing file.

Fixes: eb0570c7df23 ("block: new zoned loop block device driver")
Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 drivers/block/zloop.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/block/zloop.c b/drivers/block/zloop.c
index 9145e0f98d56..b4076940ae7f 100644
--- a/drivers/block/zloop.c
+++ b/drivers/block/zloop.c
@@ -1056,6 +1056,16 @@ static struct file *zloop_filp_open_fmt(int oflags, umode_t mode,
 		return ERR_PTR(-ENOMEM);
 	file = filp_open(p, oflags, mode);
 	kfree(p);
+	if (IS_ERR(file))
+		return file;
+
+	/* Zone files are accessed with ->read_iter() and ->write_iter(). */
+	if ((oflags & O_ACCMODE) == O_RDWR &&
+	    (!file->f_op->read_iter || !file->f_op->write_iter)) {
+		fput(file);
+		return ERR_PTR(-EINVAL);
+	}
+
 	return file;
 }
 
-- 
2.56.0