linux-hardening - Re: [PATCH][next] RDMA/cm: Avoid -Wflex-array-member-not-at-end warning

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Date: Mon, 25 Mar 2024 19:47:06 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Leon Romanovsky <leon@...nel.org>, linux-rdma@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] RDMA/cm: Avoid -Wflex-array-member-not-at-end
 warning

On Mon, Mar 25, 2024 at 02:24:07PM -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
> ready to enable it globally.
> 
> Use the `struct_group_tagged()` helper to separate the flexible array
> from the rest of the members in flexible `struct cm_work`, and avoid
> embedding the flexible-array member in `struct cm_timewait_info`.
> 
> Also, use `container_of()` to retrieve a pointer to the flexible
> structure.
> 
> So, with these changes, fix the following warning:
> drivers/infiniband/core/cm.c:196:24: 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@...nel.org>
> ---
>  drivers/infiniband/core/cm.c | 21 ++++++++++++---------
>  1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
> index bf0df6ee4f78..80c87085499c 100644
> --- a/drivers/infiniband/core/cm.c
> +++ b/drivers/infiniband/core/cm.c
> @@ -182,18 +182,21 @@ struct cm_av {
>  };
>  
>  struct cm_work {
> -	struct delayed_work work;
> -	struct list_head list;
> -	struct cm_port *port;
> -	struct ib_mad_recv_wc *mad_recv_wc;	/* Received MADs */
> -	__be32 local_id;			/* Established / timewait */
> -	__be32 remote_id;
> -	struct ib_cm_event cm_event;
> +	/* New members must be added within the struct_group() macro below. */
> +	struct_group_tagged(cm_work_hdr, hdr,
> +		struct delayed_work work;
> +		struct list_head list;
> +		struct cm_port *port;
> +		struct ib_mad_recv_wc *mad_recv_wc;	/* Received MADs */
> +		__be32 local_id;			/* Established / timewait */
> +		__be32 remote_id;
> +		struct ib_cm_event cm_event;
> +	);
>  	struct sa_path_rec path[];
>  };

I didn't look, but does it make more sense to break out the path side
into its own type and avoid the struct_group_tagged? I seem to
remember only one thing used it.

Jason