linux-hardening - Re: [PATCH v2] scsi: fc: Avoid -Wflex-array-member-not-at-end warnings

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Message-ID: <020f8c5c-c9e4-4ad0-8052-a0b182ded92c@suse.de>
Date: Wed, 27 Aug 2025 08:29:13 +0200
From: Hannes Reinecke <hare@...e.de>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Justin Tee <justin.tee@...adcom.com>, James Smart
 <james.smart@...adcom.com>, Dick Kennedy <dick.kennedy@...adcom.com>,
 "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] scsi: fc: Avoid -Wflex-array-member-not-at-end
 warnings

On 8/27/25 08:10, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end has been introduced in GCC-14, and we
> are getting ready to enable it, globally.
> 
> So, in order to avoid ending up with a flexible-array member in the
> middle of multiple other structs, we use the `__struct_group()`
> helper to create a new tagged `struct fc_df_desc_fpin_reg_hdr`.
> This structure groups together all the members of the flexible
> `struct fc_df_desc_fpin_reg` except the flexible array.
> 
> As a result, the array is effectively separated from the rest of the
> members without modifying the memory layout of the flexible structure.
> We then change the type of the middle struct members currently causing
> trouble from `struct fc_df_desc_fpin_reg` to `struct
> fc_df_desc_fpin_reg_hdr`.
> 
> We also want to ensure that in case new members need to be added to the
> flexible structure, they are always included within the newly created
> tagged struct. For this, we use `_Static_assert()`. This ensures that
> the memory layout for both the flexible structure and the new tagged
> struct is the same after any changes.
> 
> This approach avoids having to implement `struct fc_df_desc_fpin_reg_hdr`
> as a completely separate structure, thus preventing having to maintain
> two independent but basically identical structures, closing the door
> to potential bugs in the future.
> 
> The above is also done for flexible structures `struct fc_els_rdf` and
> `struct fc_els_rdf_resp`
> 
> So, with these changes, fix the following warnings:
> drivers/scsi/lpfc/lpfc_hw4.h:4936:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/scsi/lpfc/lpfc_hw4.h:4942:41: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/scsi/lpfc/lpfc_hw4.h:4947:41: 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>
> ---
> Changes in v2:
>   - Implement the same changes for `struct fc_els_rdf_resp`
>   - Fix size calculation in lpfc_issue_els_rdf(). (Justin Tee)
> 
> v1:
>   - Link: https://lore.kernel.org/linux-hardening/aJtMETERd-geyP1q@kspp/
> 
>   include/uapi/scsi/fc/fc_els.h | 58 +++++++++++++++++++++++------------
>   drivers/scsi/lpfc/lpfc_els.c  |  2 +-
>   drivers/scsi/lpfc/lpfc_hw4.h  |  6 ++--
>   3 files changed, 43 insertions(+), 23 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@...e.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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