Re: [PATCH 5/5] io_uring: add support for user mapped provided buffer ring

Ammar Faizi
2023-03-16T18:07:58Z

I tried to verify the for-next build report. And I think this doesn't
look right.

On Tue, Mar 14, 2023 at 11:16:42AM -0600, Jens Axboe wrote:
> @@ -214,15 +215,27 @@ static int __io_remove_buffers(struct io_ring_ctx *ctx,
> if (!nbufs)
> return 0;
>
> - if (bl->is_mapped && bl->buf_nr_pages) {
> - int j;
> -
> + if (bl->is_mapped) {
> i = bl->buf_ring->tail - bl->head;
^^^^^^^^^^^^^^^^^^

Dereference bl->buf_ring. It implies bl->buf_ring is not NULL.

> - for (j = 0; j < bl->buf_nr_pages; j++)
> - unpin_user_page(bl->buf_pages[j]);
> - kvfree(bl->buf_pages);
> - bl->buf_pages = NULL;
> - bl->buf_nr_pages = 0;
> + if (bl->is_mmap) {
> + if (bl->buf_ring) {
^^^^^^^^^^^^^^^^^

A NULL check against bl->buf_ring here. If it was possible to be NULL,
wouldn't the above dereference BUG()?

--
Ammar Faizi