linux-kernel - Re: [PATCH][next] wifi: ath11k: Avoid -Wflex-array-member-not-at-end warnings

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Message-ID: <0070b332-b617-4454-ac7b-85b1d78fef68@embeddedor.com>
Date: Sat, 10 Aug 2024 09:41:29 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Jeff Johnson <quic_jjohnson@...cinc.com>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, Kalle Valo
 <kvalo@...nel.org>, Jeff Johnson <jjohnson@...nel.org>
Cc: linux-wireless@...r.kernel.org, ath11k@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] wifi: ath11k: Avoid -Wflex-array-member-not-at-end
 warnings



On 09/08/24 20:21, Jeff Johnson wrote:
> On 8/9/2024 9:20 AM, Gustavo A. R. Silva wrote:
>> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
>> getting ready to enable it, globally.
>>
>> Move the conflicting declaration to the end of the structure. Notice
>> that `struct ieee80211_chanctx_conf` is a flexible structure --a
>> structure that contains a flexible-array member.
>>
>> Also, remove a couple of unused structures.
>>
>> Fix the following warnings:
>> drivers/net/wireless/ath/ath11k/core.h:409:39: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>> drivers/net/wireless/ath/ath11k/dp.h:1309:24: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>> drivers/net/wireless/ath/ath11k/dp.h:1368:24: 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/net/wireless/ath/ath11k/core.h |  4 +++-
>>   drivers/net/wireless/ath/ath11k/dp.h   | 23 -----------------------
>>   2 files changed, 3 insertions(+), 24 deletions(-)
>>
>> diff --git a/drivers/net/wireless/ath/ath11k/core.h b/drivers/net/wireless/ath/ath11k/core.h
>> index df24f0e409af..e283415dccf3 100644
>> --- a/drivers/net/wireless/ath/ath11k/core.h
>> +++ b/drivers/net/wireless/ath/ath11k/core.h
>> @@ -406,11 +406,13 @@ struct ath11k_vif {
>>   	bool wpaie_present;
>>   	bool bcca_zero_sent;
>>   	bool do_not_send_tmpl;
>> -	struct ieee80211_chanctx_conf chanctx;
>>   	struct ath11k_arp_ns_offload arp_ns_offload;
>>   	struct ath11k_rekey_data rekey_data;
>>   
>>   	struct ath11k_reg_tpc_power_info reg_tpc_info;
>> +
>> +	/* Must be last - ends in a flexible-array member. */
>> +	struct ieee80211_chanctx_conf chanctx;
> 
> there is something illogical about this since the vif is allocated using
> sizeof() and hence there will never be memory allocated for the flexible
> array, and it is assigned using either struct assignment or memcpy using the
> struct size which (fortunately) would not transfer the flexible array contents:
> 		arvif->chanctx = *ctx;
> 
> 		memcpy(&arvif->chanctx, ctx, sizeof(*ctx));

Yes; this is why I didn't include a 'Fixes' tag.

In any case, middle-flex-arrays are deprecated and should either be
removed/refactored[1][2] or placed at the very bottom in any nested
structures. :)

> 
> since ath11k doesn't actually use the drv_priv[] I guess this change is OK, it
> is just strange to me.
> 
> also makes me wonder why ath11k keeps a copy of the chanctx instead of just
> getting it from the underlying ieee80211_link_data. but that is outside the
> scope of this discussion.
> 
>>   };
>>   
>>   struct ath11k_vif_iter {
>> diff --git a/drivers/net/wireless/ath/ath11k/dp.h b/drivers/net/wireless/ath/ath11k/dp.h
>> index 2f6dd69d3be2..65d2bc0687c8 100644
>> --- a/drivers/net/wireless/ath/ath11k/dp.h
>> +++ b/drivers/net/wireless/ath/ath11k/dp.h
>> @@ -1305,18 +1305,6 @@ struct htt_ppdu_stats_user_rate {
>>   #define HTT_TX_INFO_PEERID(_flags) \
>>   			FIELD_GET(HTT_PPDU_STATS_TX_INFO_FLAGS_PEERID_M, _flags)
>>   
>> -struct htt_tx_ppdu_stats_info {
>> -	struct htt_tlv tlv_hdr;
>> -	u32 tx_success_bytes;
>> -	u32 tx_retry_bytes;
>> -	u32 tx_failed_bytes;
>> -	u32 flags; /* %HTT_PPDU_STATS_TX_INFO_FLAGS_ */
>> -	u16 tx_success_msdus;
>> -	u16 tx_retry_msdus;
>> -	u16 tx_failed_msdus;
>> -	u16 tx_duration; /* united in us */
>> -} __packed;
>> -
>>   enum  htt_ppdu_stats_usr_compln_status {
>>   	HTT_PPDU_STATS_USER_STATUS_OK,
>>   	HTT_PPDU_STATS_USER_STATUS_FILTERED,
>> @@ -1364,17 +1352,6 @@ struct htt_ppdu_stats_usr_cmpltn_ack_ba_status {
>>   	u32 success_bytes;
>>   } __packed;
>>   
>> -struct htt_ppdu_stats_usr_cmn_array {
>> -	struct htt_tlv tlv_hdr;
>> -	u32 num_ppdu_stats;
>> -	/* tx_ppdu_stats_info is filled by multiple struct htt_tx_ppdu_stats_info
>> -	 * elements.
>> -	 * tx_ppdu_stats_info is variable length, with length =
>> -	 *     number_of_ppdu_stats * sizeof (struct htt_tx_ppdu_stats_info)
>> -	 */
>> -	struct htt_tx_ppdu_stats_info tx_ppdu_info[];
>> -} __packed;
>> -
>>   struct htt_ppdu_user_stats {
>>   	u16 peer_id;
>>   	u32 tlv_flags;
> 
> the second part if definitely ok.
> 
> Acked-by: Jeff Johnson <quic_jjohnson@...cinc.com>

Thanks
--
Gustavo

[1] https://lore.kernel.org/linux-hardening/ZrOQa2gew5yadyt3@cute/
[2] https://lore.kernel.org/linux-hardening/ZrJqtUpCI+uCeb4D@cute/