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Date: Thu, 7 Mar 2024 09:17:11 +0100
From: Jan Karcher <jaka@...ux.ibm.com>
To: Wen Gu <guwen@...ux.alibaba.com>,
"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>,
"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,
Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH][next] net/smc: Avoid -Wflex-array-member-not-at-end
warnings
On 04/03/2024 10:00, Wen Gu wrote:
>
>
> On 2024/3/2 02:40, 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.
>>
>> There are currently a couple of objects in `struct
>> smc_clc_msg_proposal_area`
>> that contain a couple of flexible structures:
>>
Thank you Gustavo for the proposal.
I had to do some reading to better understand what's happening and how
your patch solves this.
>> struct smc_clc_msg_proposal_area {
>> ...
>> struct smc_clc_v2_extension pclc_v2_ext;
>> ...
>> struct smc_clc_smcd_v2_extension pclc_smcd_v2_ext;
>> ...
>> };
>>
>> So, in order to avoid ending up with a couple of flexible-array members
>> in the middle of a struct, we use the `struct_group_tagged()` helper to
>> separate the flexible array from the rest of the members in the flexible
>> structure:
>>
>> struct smc_clc_smcd_v2_extension {
>> struct_group_tagged(smc_clc_smcd_v2_extension_hdr, hdr,
>> u8 system_eid[SMC_MAX_EID_LEN];
>> u8 reserved[16];
>> );
>> struct smc_clc_smcd_gid_chid gidchid[];
>> };
>>
>> With the change described above, we now declare objects of the type of
>> the tagged struct without embedding flexible arrays in the middle of
>> another struct:
>>
>> struct smc_clc_msg_proposal_area {
>> ...
>> struct smc_clc_v2_extension_hdr pclc_v2_ext;
>> ...
>> struct smc_clc_smcd_v2_extension_hdr pclc_smcd_v2_ext;
>> ...
>> };
>>
>> We also use `container_of()` when we need to retrieve a pointer to the
>> flexible structures.
>>
>> So, with these changes, fix the following warnings:
>>
>> In file included from net/smc/af_smc.c:42:
>> net/smc/smc_clc.h:186:49: warning: structure containing a flexible
>> array member is not at the end of another structure
>> [-Wflex-array-member-not-at-end]
>> 186 | struct smc_clc_v2_extension pclc_v2_ext;
>> | ^~~~~~~~~~~
>> net/smc/smc_clc.h:188:49: warning: structure containing a flexible
>> array member is not at the end of another structure
>> [-Wflex-array-member-not-at-end]
>> 188 | struct smc_clc_smcd_v2_extension
>> pclc_smcd_v2_ext;
>> | ^~~~~~~~~~~~~~~~
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>> ---
>> net/smc/smc_clc.c | 5 +++--
>> net/smc/smc_clc.h | 24 ++++++++++++++----------
>> 2 files changed, 17 insertions(+), 12 deletions(-)
>>
>> diff --git a/net/smc/smc_clc.c b/net/smc/smc_clc.c
>> index e55026c7529c..3094cfa1c458 100644
>> --- a/net/smc/smc_clc.c
>> +++ b/net/smc/smc_clc.c
>> @@ -853,8 +853,9 @@ int smc_clc_send_proposal(struct smc_sock *smc,
>> struct smc_init_info *ini)
>> pclc_smcd = &pclc->pclc_smcd;
>> pclc_prfx = &pclc->pclc_prfx;
>> ipv6_prfx = pclc->pclc_prfx_ipv6;
>> - v2_ext = &pclc->pclc_v2_ext;
>> - smcd_v2_ext = &pclc->pclc_smcd_v2_ext;
>> + v2_ext = container_of(&pclc->pclc_v2_ext, struct
>> smc_clc_v2_extension, _hdr);
>> + smcd_v2_ext = container_of(&pclc->pclc_smcd_v2_ext,
>> + struct smc_clc_smcd_v2_extension, hdr);
>> gidchids = pclc->pclc_gidchids;
>> trl = &pclc->pclc_trl;
>> diff --git a/net/smc/smc_clc.h b/net/smc/smc_clc.h
>> index 7cc7070b9772..5b91a1947078 100644
>> --- a/net/smc/smc_clc.h
>> +++ b/net/smc/smc_clc.h
>> @@ -134,12 +134,14 @@ struct smc_clc_smcd_gid_chid {
>> */
>> struct smc_clc_v2_extension {
>> - struct smc_clnt_opts_area_hdr hdr;
>> - u8 roce[16]; /* RoCEv2 GID */
>> - u8 max_conns;
>> - u8 max_links;
>> - __be16 feature_mask;
>> - u8 reserved[12];
>> + struct_group_tagged(smc_clc_v2_extension_hdr, _hdr,
>> + struct smc_clnt_opts_area_hdr hdr;
>> + u8 roce[16]; /* RoCEv2 GID */
>> + u8 max_conns;
>> + u8 max_links;
>> + __be16 feature_mask;
>> + u8 reserved[12];
>> + );
>> u8 user_eids[][SMC_MAX_EID_LEN];
>> };
>> @@ -159,8 +161,10 @@ struct smc_clc_msg_smcd { /* SMC-D GID
>> information */
>> };
>> struct smc_clc_smcd_v2_extension {
>> - u8 system_eid[SMC_MAX_EID_LEN];
>> - u8 reserved[16];
>> + struct_group_tagged(smc_clc_smcd_v2_extension_hdr, hdr,
>> + u8 system_eid[SMC_MAX_EID_LEN];
>> + u8 reserved[16];
>> + );
>> struct smc_clc_smcd_gid_chid gidchid[];
>> };
>> @@ -183,9 +187,9 @@ struct smc_clc_msg_proposal_area {
>> struct smc_clc_msg_smcd pclc_smcd;
>> struct smc_clc_msg_proposal_prefix pclc_prfx;
>> struct smc_clc_ipv6_prefix
>> pclc_prfx_ipv6[SMC_CLC_MAX_V6_PREFIX];
>> - struct smc_clc_v2_extension pclc_v2_ext;
>> + struct smc_clc_v2_extension_hdr pclc_v2_ext;
>> u8 user_eids[SMC_CLC_MAX_UEID][SMC_MAX_EID_LEN];
>> - struct smc_clc_smcd_v2_extension pclc_smcd_v2_ext;
>> + struct smc_clc_smcd_v2_extension_hdr pclc_smcd_v2_ext;
>> struct smc_clc_smcd_gid_chid
>> pclc_gidchids[SMCD_CLC_MAX_V2_GID_ENTRIES];
>> struct smc_clc_msg_trail pclc_trl;
>
> Thank you! Gustavo. This patch can fix this warning well, just the name
> '*_hdr' might not be very accurate, but I don't have a good idea ATM.
I agree. Should we chose this option we should come up for a better name.
>
> Besides, I am wondering if this can be fixed by moving
> user_eids of smc_clc_msg_proposal_area into smc_clc_v2_extension,
> and
> pclc_gidchids of smc_clc_msg_proposal_area into smc_clc_smcd_v2_extension.
>
> so that we can avoid to use the flexible-array in smc_clc_v2_extension
> and smc_clc_smcd_v2_extension.
I like the idea and put some thought into it. The only thing that is not
perfectly clean IMO is the following:
By the current definition it is easily visible that we are dealing with
a variable sized array. If we move them into the structs one could think
they are always at their MAX size which they are not.
E.g.: An incoming proposal can have 0 UEIDs indicated by the eid_cnt.
That said nothing a comment can't fix.
From what i have seen the offset and length calculations regarding the
"real" size of those structs is fine with your proposal.
Can you verify that your changes also resolve the warnings?
[...]
> };
>
>
> Thanks!
> Wen Gu
Thanks you
- Jan
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