Re: [PATCH v2][next] w1: Avoid -Wflex-array-member-not-at-end warnings

Kees Cook
2025-04-07T20:26:31Z

On Mon, Apr 07, 2025 at 01:36:26PM -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
>
> Use the `DEFINE_RAW_FLEX()` helper for on-stack definitions of
> a flexible structure where the size of the flexible-array member
> is known at compile-time, and refactor the rest of the code,
> accordingly.
>
> So, with these changes, fix the following warnings:
>
> drivers/w1/w1_netlink.c:198:31: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/w1/w1_netlink.c:219:31: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
> Changes in v2:
> - Fix memcpy() instance - use new pointer `pkg_msg`, instead of `packet`. (Kees)

Thanks! You didn't want to use object assignments? Those are type
checked. :)

Reviewed-by: Kees Cook <kees@kernel.org>

-Kees

>
> v1:
> - Link: https://lore.kernel.org/linux-hardening/Z-WD2NP_1A0ratnI@kspp/
>
> drivers/w1/w1_netlink.c | 42 ++++++++++++++++++++---------------------
> 1 file changed, 20 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/w1/w1_netlink.c b/drivers/w1/w1_netlink.c
> index 691978cddab7..724a008cf342 100644
> --- a/drivers/w1/w1_netlink.c
> +++ b/drivers/w1/w1_netlink.c
> @@ -194,16 +194,16 @@ static void w1_netlink_queue_status(struct w1_cb_block *block,
> static void w1_netlink_send_error(struct cn_msg *cn, struct w1_netlink_msg *msg,
> int portid, int error)
> {
> - struct {
> - struct cn_msg cn;
> - struct w1_netlink_msg msg;
> - } packet;
> - memcpy(&packet.cn, cn, sizeof(packet.cn));
> - memcpy(&packet.msg, msg, sizeof(packet.msg));
> - packet.cn.len = sizeof(packet.msg);
> - packet.msg.len = 0;
> - packet.msg.status = (u8)-error;
> - cn_netlink_send(&packet.cn, portid, 0, GFP_KERNEL);
> + DEFINE_RAW_FLEX(struct cn_msg, packet, data,
> + sizeof(struct w1_netlink_msg));
> + struct w1_netlink_msg *pkt_msg = (struct w1_netlink_msg *)packet->data;
> +
> + memcpy(packet, cn, sizeof(*packet));
> + memcpy(pkt_msg, msg, sizeof(*pkt_msg));
> + packet->len = sizeof(*pkt_msg);
> + pkt_msg->len = 0;
> + pkt_msg->status = (u8)-error;
> + cn_netlink_send(packet, portid, 0, GFP_KERNEL);
> }
>
> /**
> @@ -215,22 +215,20 @@ static void w1_netlink_send_error(struct cn_msg *cn, struct w1_netlink_msg *msg,
> */
> void w1_netlink_send(struct w1_master *dev, struct w1_netlink_msg *msg)
> {
> - struct {
> - struct cn_msg cn;
> - struct w1_netlink_msg msg;
> - } packet;
> - memset(&packet, 0, sizeof(packet));
> + DEFINE_RAW_FLEX(struct cn_msg, packet, data,
> + sizeof(struct w1_netlink_msg));
> + struct w1_netlink_msg *pkg_msg = (struct w1_netlink_msg *)packet->data;
>
> - packet.cn.id.idx = CN_W1_IDX;
> - packet.cn.id.val = CN_W1_VAL;
> + packet->id.idx = CN_W1_IDX;
> + packet->id.val = CN_W1_VAL;
>
> - packet.cn.seq = dev->seq++;
> - packet.cn.len = sizeof(*msg);
> + packet->seq = dev->seq++;
> + packet->len = sizeof(*msg);
>
> - memcpy(&packet.msg, msg, sizeof(*msg));
> - packet.msg.len = 0;
> + memcpy(pkg_msg, msg, sizeof(*msg));
> + pkg_msg->len = 0;
>
> - cn_netlink_send(&packet.cn, 0, 0, GFP_KERNEL);
> + cn_netlink_send(packet, 0, 0, GFP_KERNEL);
> }
>
> static void w1_send_slave(struct w1_master *dev, u64 rn)
> --
> 2.43.0
>

--
Kees Cook