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

[Dylan Yudaken <dylany@fb.com>]

On Mon, 2022-05-09 at 12:06 +0000, Dylan Yudaken wrote:
> 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);
> 

The following seems to fix it for me. I can submit it separately if you
like.

diff --git a/fs/io_uring.c b/fs/io_uring.c
index b6d491c9a25f..22699cb359e9 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5630,7 +5630,6 @@ static int io_recv(struct io_kiocb *req, unsigned
int issue_flags)
 {
 	struct io_sr_msg *sr = &req->sr_msg;
 	struct msghdr msg;
-	void __user *buf = sr->buf;
 	struct socket *sock;
 	struct iovec iov;
 	unsigned flags;
@@ -5654,7 +5653,7 @@ static int io_recv(struct io_kiocb *req, unsigned
int issue_flags)
 		sr->buf = buf;
 	}
 
-	ret = import_single_range(READ, buf, sr->len, &iov,
&msg.msg_iter);
+	ret = import_single_range(READ, sr->buf, sr->len, &iov,
&msg.msg_iter);
 	if (unlikely(ret))
 		goto out_free;