On Mon, 2025-03-03 at 14:18 +0100, Markus Elfring wrote:
> From: Markus Elfring <elfring@xxxxxxxxxxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxxxxxxxxxx>
> ---
> 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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