linux-kernel - Re: [PATCH] loop: Add sanity check for read/write

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Message-ID: <CAFj5m9LVuekp_n6pEfs17n6QB3Q0yu-qRP67NOJb9ZXRNyhP3Q@mail.gmail.com>
Date: Fri, 25 Apr 2025 12:20:21 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Lizhi Xu <lizhi.xu@...driver.com>
Cc: syzbot+6af973a3b8dfd2faefdc@...kaller.appspotmail.com, axboe@...nel.dk, 
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] loop: Add sanity check for read/write_iter

On Fri, Apr 25, 2025 at 11:41 AM Lizhi Xu <lizhi.xu@...driver.com> wrote:
>
> 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@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=6af973a3b8dfd2faefdc
> Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
> ---
>  drivers/block/loop.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 674527d770dc..4f968e3071ed 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -449,10 +449,15 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
>         cmd->iocb.ki_flags = IOCB_DIRECT;
>         cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
>
> -       if (rw == ITER_SOURCE)
> -               ret = file->f_op->write_iter(&cmd->iocb, &iter);
> -       else
> -               ret = file->f_op->read_iter(&cmd->iocb, &iter);
> +       ret = 0;
> +       if (rw == ITER_SOURCE) {
> +               if (likely(file->f_op->write_iter))
> +                       ret = file->f_op->write_iter(&cmd->iocb, &iter);
> +       }
> +       else {
> +               if (likely(file->f_op->read_iter))
> +                       ret = file->f_op->read_iter(&cmd->iocb, &iter);
> +       }

The check can be added in loop_configure()/loop_change_fd()
instead of fast IO path.

Thanks,