[PATCH V2] loop: Add sanity check for read/write_iter

[Lizhi Xu]

Some file systems do not support read_iter or write_iter, such as selinuxfs
in this issue.
So before calling them, first confirm that the interface is supported and
then call it.

Reported-by: syzbot+6af973a3b8dfd2faefdc@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=6af973a3b8dfd2faefdc
Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
---
V1 -> V2: move check to loop_configure and loop_change_fd

 drivers/block/loop.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 674527d770dc..d2651e3b5142 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -603,6 +603,12 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 	if (!file)
 		return -EBADF;
 
+	if (unlikely(!file->f_op->read_iter))
+		return -EINVAL;
+
+	if (file->f_mode & FMODE_WRITE && unlikely(!file->f_op->write_iter))
+		return -EINVAL;
+
 	/* suppress uevents while reconfiguring the device */
 	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 1);
 
@@ -1039,6 +1045,14 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode,
 
 	if (!file)
 		return -EBADF;
+
+	if (unlikely(!file->f_op->read_iter))
+		return -EINVAL;
+
+	if (((file->f_mode & FMODE_WRITE) || (mode & BLK_OPEN_WRITE)) &&
+	    unlikely(!file->f_op->write_iter))
+		return -EINVAL;
+
 	is_loop = is_loop_device(file);
 
 	/* This is safe, since we have a reference from open(). */
-- 
2.43.0