linux-kernel - Re: [PATCH AUTOSEL 6.11 48/76] fuse: allow O_PATH fd for FUSE_DEV_IOC_BACKING

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Message-ID: <CAJfpegtNF6CkSsE7yWq8-4W7HP3aOjE4xnAzJp0uiU-S7Wb8pg@mail.gmail.com>
Date: Mon, 7 Oct 2024 12:15:45 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Sasha Levin <sashal@...nel.org>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
	Miklos Szeredi <mszeredi@...hat.com>, Amir Goldstein <amir73il@...il.com>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 6.11 48/76] fuse: allow O_PATH fd for FUSE_DEV_IOC_BACKING_OPEN

On Fri, 4 Oct 2024 at 20:19, Sasha Levin <sashal@...nel.org> wrote:
>
> From: Miklos Szeredi <mszeredi@...hat.com>
>
> [ Upstream commit efad7153bf93db8565128f7567aab1d23e221098 ]
>
> 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@...il.com>
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  fs/fuse/passthrough.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
> index 9666d13884ce5..62aee8289d110 100644
> --- 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);

That's a stray debug line that wasn't in there when I posted the patch
for review[1], but somehow made it into the pull...

Since this isn't a bug fix, it would be easiest to just drop the patch
from the stable queues.

But I'm okay with just dropping this stray line from the backport, or
waiting for an upstream fix which does that.

Thanks,
Miklos

[1] https://lore.kernel.org/all/20240913104703.1673180-1-mszeredi@redhat.com/