fuse: allow O_PATH fd for FUSE_DEV_IOC_BACKING_OPEN

Only f_path is used from backing files registered with
FUSE_DEV_IOC_BACKING_OPEN, so it makes sense to allow O_PATH descriptors.

O_PATH files have an empty f_op, so don't check read_iter/write_iter.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
index 9666d13884ce59175a844f85082c442cadbdf354..62aee8289d11053e9ad66155c20b9ff9c5c92f96 100644 (file)
--- a/fs/fuse/passthrough.c
+++ b/fs/fuse/passthrough.c
@@ -228,16 +228,13 @@ int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
        if (map->flags || map->padding)
                goto out;
 
-       file = fget(map->fd);
+       file = fget_raw(map->fd);
        res = -EBADF;
        if (!file)
                goto out;
 
-       res = -EOPNOTSUPP;
-       if (!file->f_op->read_iter || !file->f_op->write_iter)
-               goto out_fput;
-
        backing_sb = file_inode(file)->i_sb;
+       pr_info("%s: %x:%pD %i\n", __func__, backing_sb->s_dev, file, backing_sb->s_stack_depth);
        res = -ELOOP;
        if (backing_sb->s_stack_depth >= fc->max_stack_depth)
                goto out_fput;