netdev - Re: [PATCH][next] net/smc: Use static_assert() to check struct sizes

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Message-ID: <90da4cb0-a422-405d-b5f9-99eba490071f@linux.ibm.com>
Date: Mon, 12 Aug 2024 08:29:26 +0200
From: Jan Karcher <jaka@...ux.ibm.com>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        "D. Wythe" <alibuda@...ux.alibaba.com>,
        Tony Lu <tonylu@...ux.alibaba.com>, Wen Gu <guwen@...ux.alibaba.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc: linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] net/smc: Use static_assert() to check struct sizes



On 09/08/2024 00:07, Gustavo A. R. Silva wrote:
> Commit 9748dbc9f265 ("net/smc: Avoid -Wflex-array-member-not-at-end
> warnings") introduced tagged `struct smc_clc_v2_extension_fixed` and
> `struct smc_clc_smcd_v2_extension_fixed`. We want to ensure that when
> new members need to be added to the flexible structures, they are
> always included within these tagged structs.
> 
> So, we use `static_assert()` to ensure that the memory layout for
> both the flexible structure and the tagged struct is the same after
> any changes.

Read up what the macro does. I like it.
Compile tested on s390.

Reviewed-by: Jan Karcher <jaka@...ux.ibm.com>

> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>   net/smc/smc_clc.h | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/net/smc/smc_clc.h b/net/smc/smc_clc.h
> index 467effb50cd6..5625fda2960b 100644
> --- a/net/smc/smc_clc.h
> +++ b/net/smc/smc_clc.h
> @@ -145,6 +145,8 @@ struct smc_clc_v2_extension {
>   	);
>   	u8 user_eids[][SMC_MAX_EID_LEN];
>   };
> +static_assert(offsetof(struct smc_clc_v2_extension, user_eids) == sizeof(struct smc_clc_v2_extension_fixed),
> +	      "struct member likely outside of struct_group_tagged()");
>   
>   struct smc_clc_msg_proposal_prefix {	/* prefix part of clc proposal message*/
>   	__be32 outgoing_subnet;	/* subnet mask */
> @@ -169,6 +171,8 @@ struct smc_clc_smcd_v2_extension {
>   	);
>   	struct smc_clc_smcd_gid_chid gidchid[];
>   };
> +static_assert(offsetof(struct smc_clc_smcd_v2_extension, gidchid) == sizeof(struct smc_clc_smcd_v2_extension_fixed),
> +	      "struct member likely outside of struct_group_tagged()");
>   
>   struct smc_clc_msg_proposal {	/* clc proposal message sent by Linux */
>   	struct smc_clc_msg_hdr hdr;