Re: [PATCH v2] io_uring: Replace 0-length array with flexible array

From: Gustavo A. R. Silva
Date: Fri Jan 06 2023 - 10:53:32 EST


On Thu, Jan 05, 2023 at 11:05:11AM -0800, Kees Cook wrote:
> Zero-length arrays are deprecated[1]. Replace struct io_uring_buf_ring's
> "bufs" with a flexible array member. (How is the size of this array
> verified?) Detected with GCC 13, using -fstrict-flex-arrays=3:
>
> In function 'io_ring_buffer_select',
> inlined from 'io_buffer_select' at io_uring/kbuf.c:183:10:
> io_uring/kbuf.c:141:23: warning: array subscript 255 is outside the bounds of an interior zero-length array 'struct io_uring_buf[0]' [-Wzero-length-bounds]
> 141 | buf = &br->bufs[head];
> | ^~~~~~~~~~~~~~~
> In file included from include/linux/io_uring.h:7,
> from io_uring/kbuf.c:10:
> include/uapi/linux/io_uring.h: In function 'io_buffer_select':
> include/uapi/linux/io_uring.h:628:41: note: while referencing 'bufs'
> 628 | struct io_uring_buf bufs[0];
> | ^~~~
>
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
>
> Fixes: c7fb19428d67 ("io_uring: add support for ring mapped supplied buffers")
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Pavel Begunkov <asml.silence@xxxxxxxxx>
> Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: io-uring@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>

Thanks!
--
Gustavo

> ---
> v2: use helper since these flex arrays are in a union.
> v1: https://lore.kernel.org/lkml/20230105033743.never.628-kees@xxxxxxxxxx
> ---
> include/uapi/linux/io_uring.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 2780bce62faf..434f62e0fb72 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -625,7 +625,7 @@ struct io_uring_buf_ring {
> __u16 resv3;
> __u16 tail;
> };
> - struct io_uring_buf bufs[0];
> + __DECLARE_FLEX_ARRAY(struct io_uring_buf, bufs);
> };
> };
>
> --
> 2.34.1
>