Re: [PATCH RESEND] iwlwifi: Adjust input parameter validation in iwl_sta_calc_ht_flags()

["Berg, Benjamin" <benjamin.berg@intel.com>]

On Mon, 2025-03-03 at 14:18 +0100, Markus Elfring wrote:
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Wed, 19 Apr 2023 19:19:34 +0200
> 
> The address of a data structure member was determined before
> a corresponding null pointer check in the implementation of
> the function “iwl_sta_calc_ht_flags”.
> 
> Thus avoid the risk for undefined behaviour by moving the assignment
> for the variable “sta_ht_inf” behind the null pointer check.

I am a bit confused, I don't see any risk of undefined behaviour here.

The change is obviously fine, and I guess one can argue that it is less
confusing as the compiler will generate a warning if one uses the
variable before assignment.

However, the code is both well defined and correct. If sta is NULL then
sta_ht_inf is never used, so the fact that it is effectively a NULL
pointer [offsetof(struct ieee80211_sta, deflink.ht_cap)] does not
matter.

Benjamin

> This issue was detected by using the Coccinelle software.
> 
> Fixes: 046d2e7c50e3 ("mac80211: prepare sta handling for MLO
> support")
> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> ---
>  drivers/net/wireless/intel/iwlwifi/dvm/sta.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/dvm/sta.c
> b/drivers/net/wireless/intel/iwlwifi/dvm/sta.c
> index cef43cf80620..74814ce0155e 100644
> --- a/drivers/net/wireless/intel/iwlwifi/dvm/sta.c
> +++ b/drivers/net/wireless/intel/iwlwifi/dvm/sta.c
> @@ -147,7 +147,7 @@ static void iwl_sta_calc_ht_flags(struct iwl_priv
> *priv,
>  				  struct iwl_rxon_context *ctx,
>  				  __le32 *flags, __le32 *mask)
>  {
> -	struct ieee80211_sta_ht_cap *sta_ht_inf = &sta-
> >deflink.ht_cap;
> +	struct ieee80211_sta_ht_cap *sta_ht_inf;
> 
>  	*mask = STA_FLG_RTS_MIMO_PROT_MSK |
>  		STA_FLG_MIMO_DIS_MSK |
> @@ -156,7 +156,11 @@ static void iwl_sta_calc_ht_flags(struct
> iwl_priv *priv,
>  		STA_FLG_AGG_MPDU_DENSITY_MSK;
>  	*flags = 0;
> 
> -	if (!sta || !sta_ht_inf->ht_supported)
> +	if (!sta)
> +		return;
> +
> +	sta_ht_inf = &sta->deflink.ht_cap;
> +	if (!sta_ht_inf->ht_supported)
>  		return;
> 
>  	IWL_DEBUG_INFO(priv, "STA %pM SM PS mode: %s\n",
> --
> 2.40.0
> 

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