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

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Date: Mon, 25 Mar 2024 20:57:08 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Jason Gunthorpe <jgg@...pe.ca>,
 "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 3/25/24 16:47, Jason Gunthorpe wrote:
> 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.
> 

I thought about that, but I'd have to change the parameter type of
`static int cm_timewait_handler(struct cm_work *work)`, and that would
imply also modifying the internals of function `cm_work_handler()` (and
then I didn't look much into it). So, the `struct_group_tagged()`
strategy is in general more cleaner and straightforward.

--
Gustavo