Re: [PATCH v3] wifi: mwifiex: Refactor 1-element array into flexible array in struct mwifiex_ie_types_chan_list_param_set

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 2/7/24 04:30, Kees Cook wrote:
> struct mwifiex_ie_types_chan_list_param_set::chan_scan_param is treated
> as a flexible array, so convert it into one so that it doesn't trip
> the array bounds sanitizer[1]. Only a few places were using sizeof()
> on the whole struct, so adjust those to follow the calculation pattern
> to avoid including the trailing single element.
> 
> Examining binary output differences doesn't appear to show any literal
> size values changing, though it is obfuscated a bit by the compiler
> adjusting register usage and stack spill slots, etc.
> 
> Link: https://github.com/KSPP/linux/issues/51 [1]
> Cc: Brian Norris <briannorris@chromium.org>
> Cc: Kalle Valo <kvalo@kernel.org>
> Cc: Dmitry Antipov <dmantipov@yandex.ru>
> Cc: Johannes Berg <johannes.berg@intel.com>
> Cc: zuoqilin <zuoqilin@yulong.com>
> Cc: Ruan Jinjie <ruanjinjie@huawei.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
> Cc: linux-wireless@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

TLV and one-element arrays are always tricky to transform (into flex arrays),
but (unless I'm missing something that the maintainers might point out) this
looks good to me.

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
--
Gustavo

> ---
> v3: catch two more cases of changed sizeof (gustavo)
> v2: https://lore.kernel.org/linux-hardening/20240206183857.it.362-kees@kernel.org/
> v1: https://lore.kernel.org/linux-hardening/20240206163501.work.158-kees@kernel.org/
> ---
>   drivers/net/wireless/marvell/mwifiex/11n.c  | 12 +++++-------
>   drivers/net/wireless/marvell/mwifiex/fw.h   |  2 +-
>   drivers/net/wireless/marvell/mwifiex/scan.c | 14 ++++++--------
>   3 files changed, 12 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/wireless/marvell/mwifiex/11n.c b/drivers/net/wireless/marvell/mwifiex/11n.c
> index 90e401100898..c0c635e74bc5 100644
> --- a/drivers/net/wireless/marvell/mwifiex/11n.c
> +++ b/drivers/net/wireless/marvell/mwifiex/11n.c
> @@ -392,12 +392,10 @@ mwifiex_cmd_append_11n_tlv(struct mwifiex_private *priv,
>   
>   		chan_list =
>   			(struct mwifiex_ie_types_chan_list_param_set *) *buffer;
> -		memset(chan_list, 0,
> -		       sizeof(struct mwifiex_ie_types_chan_list_param_set));
> +		memset(chan_list, 0, struct_size(chan_list, chan_scan_param, 1));
>   		chan_list->header.type = cpu_to_le16(TLV_TYPE_CHANLIST);
> -		chan_list->header.len = cpu_to_le16(
> -			sizeof(struct mwifiex_ie_types_chan_list_param_set) -
> -			sizeof(struct mwifiex_ie_types_header));
> +		chan_list->header.len =
> +			cpu_to_le16(sizeof(struct mwifiex_chan_scan_param_set));
>   		chan_list->chan_scan_param[0].chan_number =
>   			bss_desc->bcn_ht_oper->primary_chan;
>   		chan_list->chan_scan_param[0].radio_type =
> @@ -411,8 +409,8 @@ mwifiex_cmd_append_11n_tlv(struct mwifiex_private *priv,
>   					  (bss_desc->bcn_ht_oper->ht_param &
>   					  IEEE80211_HT_PARAM_CHA_SEC_OFFSET));
>   
> -		*buffer += sizeof(struct mwifiex_ie_types_chan_list_param_set);
> -		ret_len += sizeof(struct mwifiex_ie_types_chan_list_param_set);
> +		*buffer += struct_size(chan_list, chan_scan_param, 1);
> +		ret_len += struct_size(chan_list, chan_scan_param, 1);
>   	}
>   
>   	if (bss_desc->bcn_bss_co_2040) {
> diff --git a/drivers/net/wireless/marvell/mwifiex/fw.h b/drivers/net/wireless/marvell/mwifiex/fw.h
> index 62f3c9a52a1d..3adc447b715f 100644
> --- a/drivers/net/wireless/marvell/mwifiex/fw.h
> +++ b/drivers/net/wireless/marvell/mwifiex/fw.h
> @@ -770,7 +770,7 @@ struct mwifiex_chan_scan_param_set {
>   
>   struct mwifiex_ie_types_chan_list_param_set {
>   	struct mwifiex_ie_types_header header;
> -	struct mwifiex_chan_scan_param_set chan_scan_param[1];
> +	struct mwifiex_chan_scan_param_set chan_scan_param[];
>   } __packed;
>   
>   struct mwifiex_ie_types_rxba_sync {
> diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
> index a2ddac363b10..0326b121747c 100644
> --- a/drivers/net/wireless/marvell/mwifiex/scan.c
> +++ b/drivers/net/wireless/marvell/mwifiex/scan.c
> @@ -664,15 +664,14 @@ mwifiex_scan_channel_list(struct mwifiex_private *priv,
>   
>   			/* Copy the current channel TLV to the command being
>   			   prepared */
> -			memcpy(chan_tlv_out->chan_scan_param + tlv_idx,
> +			memcpy(&chan_tlv_out->chan_scan_param[tlv_idx],
>   			       tmp_chan_list,
> -			       sizeof(chan_tlv_out->chan_scan_param));
> +			       sizeof(*chan_tlv_out->chan_scan_param));
>   
>   			/* Increment the TLV header length by the size
>   			   appended */
>   			le16_unaligned_add_cpu(&chan_tlv_out->header.len,
> -					       sizeof(
> -						chan_tlv_out->chan_scan_param));
> +					       sizeof(*chan_tlv_out->chan_scan_param));
>   
>   			/*
>   			 * The tlv buffer length is set to the number of bytes
> @@ -2369,12 +2368,11 @@ int mwifiex_cmd_802_11_bg_scan_config(struct mwifiex_private *priv,
>   		     chan_idx < MWIFIEX_BG_SCAN_CHAN_MAX &&
>   		     bgscan_cfg_in->chan_list[chan_idx].chan_number;
>   		     chan_idx++) {
> -			temp_chan = chan_list_tlv->chan_scan_param + chan_idx;
> +			temp_chan = &chan_list_tlv->chan_scan_param[chan_idx];
>   
>   			/* Increment the TLV header length by size appended */
>   			le16_unaligned_add_cpu(&chan_list_tlv->header.len,
> -					       sizeof(
> -					       chan_list_tlv->chan_scan_param));
> +					       sizeof(*chan_list_tlv->chan_scan_param));
>   
>   			temp_chan->chan_number =
>   				bgscan_cfg_in->chan_list[chan_idx].chan_number;
> @@ -2413,7 +2411,7 @@ int mwifiex_cmd_802_11_bg_scan_config(struct mwifiex_private *priv,
>   							   chan_scan_param);
>   		le16_unaligned_add_cpu(&chan_list_tlv->header.len,
>   				       chan_num *
> -			     sizeof(chan_list_tlv->chan_scan_param[0]));
> +			     sizeof(*chan_list_tlv->chan_scan_param));
>   	}
>   
>   	tlv_pos += (sizeof(chan_list_tlv->header)