[PATCH 5.10 517/717] io_uring: fix 0-iov read buffer select

[Greg Kroah-Hartman]

From: Pavel Begunkov <asml.sile...@gmail.com>

commit dd20166236953c8cd14f4c668bf972af32f0c6be upstream.

Doing vectored buf-select read with 0 iovec passed is meaningless and
utterly broken, forbid it.

Cc: <sta...@vger.kernel.org> # 5.7+
Signed-off-by: Pavel Begunkov <asml.sile...@gmail.com>
Signed-off-by: Jens Axboe <ax...@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 fs/io_uring.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3048,9 +3048,7 @@ static ssize_t io_iov_buffer_select(stru
                iov[0].iov_len = kbuf->len;
                return 0;
        }
-       if (!req->rw.len)
-               return 0;
-       else if (req->rw.len > 1)
+       if (req->rw.len != 1)
                return -EINVAL;
 
 #ifdef CONFIG_COMPAT