[PATCH mt76 2/2] wifi: mt76: adjust BSS conf pointer handling

[Fedor Pchelkin <pchelkin@ispras.ru>]

Passing a BSS conf pointer to mt76_connac2_mac_tx_rate_val() currently has
two inconsistencies.

When called from mt76_connac2_mac_write_txwi(), BSS conf is got by
dereferencing a vif pointer.  A NULL vif isn't accounted for though the
function itself supposes it to be NULL and tries to handle this case in
previous checks.  This looks like a cosmetic change since the drivers
calling the function (namely, mt7915 and mt7921) set WANT_MONITOR_VIF flag
so judging by info->control.vif initialization inside ieee80211_tx_*()
routines it can't actually come as NULL here.

The same holds for the BSS conf pointer handling inside
mt76_connac2_mac_tx_rate_val().  It is dereferenced before being checked
for NULL.  The function supposes to handle the case so reorder the check
and dereference of the pointer.  Again, this looks like a syntax issue
only.

Found by Linux Verification Center (linuxtesting.org) with SVACE static
analysis tool.

Co-developed-by: Matvey Kovalev <matvey.kovalev@ispras.ru>
Signed-off-by: Matvey Kovalev <matvey.kovalev@ispras.ru>
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
---
 .../wireless/mediatek/mt76/mt76_connac_mac.c  | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt76_connac_mac.c b/drivers/net/wireless/mediatek/mt76/mt76_connac_mac.c
index 7af6a578562f..3304b5971be0 100644
--- a/drivers/net/wireless/mediatek/mt76/mt76_connac_mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt76_connac_mac.c
@@ -297,16 +297,18 @@ u16 mt76_connac2_mac_tx_rate_val(struct mt76_phy *mphy,
 				 struct ieee80211_bss_conf *conf,
 				 bool beacon, bool mcast)
 {
-	struct mt76_vif_link *mvif = mt76_vif_conf_link(mphy->dev, conf->vif, conf);
-	struct cfg80211_chan_def *chandef = mvif->ctx ?
-					    &mvif->ctx->def : &mphy->chandef;
-	u8 nss = 0, mode = 0, band = chandef->chan->band;
-	int rateidx = 0, mcast_rate;
-	int offset = 0;
+	u8 nss = 0, mode = 0, band = NL80211_BAND_2GHZ;
+	int rateidx = 0, offset = 0, mcast_rate;
+	struct cfg80211_chan_def *chandef;
+	struct mt76_vif_link *mvif;
 
 	if (!conf)
 		goto legacy;
 
+	mvif = mt76_vif_conf_link(mphy->dev, conf->vif, conf);
+	chandef = mvif->ctx ? &mvif->ctx->def : &mphy->chandef;
+	band = chandef->chan->band;
+
 	if (is_mt7921(mphy->dev)) {
 		rateidx = ffs(conf->basic_rates) - 1;
 		goto legacy;
@@ -584,8 +586,9 @@ void mt76_connac2_mac_write_txwi(struct mt76_dev *dev, __le32 *txwi,
 		struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 		bool multicast = ieee80211_is_data(hdr->frame_control) &&
 				 is_multicast_ether_addr(hdr->addr1);
-		u16 rate = mt76_connac2_mac_tx_rate_val(mphy, &vif->bss_conf, beacon,
-							multicast);
+		u16 rate = mt76_connac2_mac_tx_rate_val(mphy,
+							vif ? &vif->bss_conf : NULL,
+							beacon, multicast);
 		u32 val = MT_TXD6_FIXED_BW;
 
 		/* hardware won't add HTC for mgmt/ctrl frame */
-- 
2.51.0