Commit f5c84eff authored by Lizhi Xu's avatar Lizhi Xu Committed by Jens Axboe
Browse files

loop: Add sanity check for read/write_iter 



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

It is releavant in that vfs_iter_read/write have the check, and removal
of their used caused szybot to be able to hit this issue.

Fixes: f2fed441 ("loop: stop using vfs_iter__{read,write} for buffered I/O")
Reported-by: default avatar <syzbot+6af973a3b8dfd2faefdc@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=6af973a3b8dfd2faefdc


Signed-off-by: default avatarLizhi Xu <lizhi.xu@windriver.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250428143626.3318717-1-lizhi.xu@windriver.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 6d732e8d

drivers/block/loop.c

+23 −0
Original line number Diff line number Diff line
@@ -505,6 +505,17 @@ static void loop_assign_backing_file(struct loop_device *lo, struct file *file) 
	lo->lo_min_dio_size = loop_query_min_dio_size(lo);

}



static int loop_check_backing_file(struct file *file)

{

	if (!file->f_op->read_iter)

		return -EINVAL;



	if ((file->f_mode & FMODE_WRITE) && !file->f_op->write_iter)

		return -EINVAL;



	return 0;

}



/*

 * loop_change_fd switched the backing store of a loopback device to

 * a new file. This is useful for operating system installers to free up
@@ -526,6 +537,10 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, 
	if (!file)

		return -EBADF;



	error = loop_check_backing_file(file);

	if (error)

		return error;



	/* suppress uevents while reconfiguring the device */

	dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 1);
@@ -963,6 +978,14 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode, 


	if (!file)

		return -EBADF;



	if ((mode & BLK_OPEN_WRITE) && !file->f_op->write_iter)

		return -EINVAL;



	error = loop_check_backing_file(file);

	if (error)

		return error;



	is_loop = is_loop_device(file);



	/* This is safe, since we have a reference from open(). */