Re: [PATCH 03/16] io_uring: make io_buffer_select() return the user address directly

[Dylan Yudaken <dylany@fb.com>]

On Sun, 2022-05-01 at 14:56 -0600, Jens Axboe wrote:
> There's no point in having callers provide a kbuf, we're just
> returning
> the address anyway.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  fs/io_uring.c | 42 ++++++++++++++++++------------------------
>  1 file changed, 18 insertions(+), 24 deletions(-)
> 

...

> @@ -6013,10 +6006,11 @@ static int io_recv(struct io_kiocb *req,
> unsigned int issue_flags)
>                 return -ENOTSOCK;
>  
>         if (req->flags & REQ_F_BUFFER_SELECT) {
> -               kbuf = io_buffer_select(req, &sr->len, sr->bgid,
> issue_flags);
> -               if (IS_ERR(kbuf))
> -                       return PTR_ERR(kbuf);
> -               buf = u64_to_user_ptr(kbuf->addr);
> +               void __user *buf;

this now shadows the outer buf, and so does not work at all as the buf
value is lost.
A bit surprised this did not show up in any tests.

> +
> +               buf = io_buffer_select(req, &sr->len, sr->bgid,
> issue_flags);
> +               if (IS_ERR(buf))
> +                       return PTR_ERR(buf);
>         }
>  
>         ret = import_single_range(READ, buf, sr->len, &iov,
> &msg.msg_iter);