wifi: wfx: fix possible NULL pointer dereference in wfx_set_mfp_ap()

Since 'ieee80211_beacon_get()' can return NULL, 'wfx_set_mfp_ap()'
should check the return value before examining skb data. So convert
the latter to return an appropriate error code and propagate it to
return from 'wfx_start_ap()' as well. Compile tested only.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Tested-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Acked-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231204171130.141394-1-dmantipov@yandex.ru

drivers/net/wireless/silabs/wfx/sta.c

@@ -336,29 +336,38 @@ static int wfx_upload_ap_templates(struct wfx_vif *wvif)
 	return 0;
 }
 
-static void wfx_set_mfp_ap(struct wfx_vif *wvif)
+static int wfx_set_mfp_ap(struct wfx_vif *wvif)
 {
 	struct ieee80211_vif *vif = wvif_to_vif(wvif);
 	struct sk_buff *skb = ieee80211_beacon_get(wvif->wdev->hw, vif, 0);
 	const int ieoffset = offsetof(struct ieee80211_mgmt, u.beacon.variable);
-	const u16 *ptr = (u16 *)cfg80211_find_ie(WLAN_EID_RSN, skb->data + ieoffset,
-						 skb->len - ieoffset);
 	const int pairwise_cipher_suite_count_offset = 8 / sizeof(u16);
 	const int pairwise_cipher_suite_size = 4 / sizeof(u16);
 	const int akm_suite_size = 4 / sizeof(u16);
+	const u16 *ptr;
 
-	if (ptr) {
-		ptr += pairwise_cipher_suite_count_offset;
-		if (WARN_ON(ptr > (u16 *)skb_tail_pointer(skb)))
-			return;
-		ptr += 1 + pairwise_cipher_suite_size * *ptr;
-		if (WARN_ON(ptr > (u16 *)skb_tail_pointer(skb)))
-			return;
-		ptr += 1 + akm_suite_size * *ptr;
-		if (WARN_ON(ptr > (u16 *)skb_tail_pointer(skb)))
-			return;
-		wfx_hif_set_mfp(wvif, *ptr & BIT(7), *ptr & BIT(6));
-	}
+	if (unlikely(!skb))
+		return -ENOMEM;
+
+	ptr = (u16 *)cfg80211_find_ie(WLAN_EID_RSN, skb->data + ieoffset,
+				      skb->len - ieoffset);
+	if (unlikely(!ptr))
+		return -EINVAL;
+
+	ptr += pairwise_cipher_suite_count_offset;
+	if (WARN_ON(ptr > (u16 *)skb_tail_pointer(skb)))
+		return -EINVAL;
+
+	ptr += 1 + pairwise_cipher_suite_size * *ptr;
+	if (WARN_ON(ptr > (u16 *)skb_tail_pointer(skb)))
+		return -EINVAL;
+
+	ptr += 1 + akm_suite_size * *ptr;
+	if (WARN_ON(ptr > (u16 *)skb_tail_pointer(skb)))
+		return -EINVAL;
+
+	wfx_hif_set_mfp(wvif, *ptr & BIT(7), *ptr & BIT(6));
+	return 0;
 }
 
 int wfx_start_ap(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
@@ -376,8 +385,7 @@ int wfx_start_ap(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 	ret = wfx_hif_start(wvif, &vif->bss_conf, wvif->channel);
 	if (ret > 0)
 		return -EIO;
-	wfx_set_mfp_ap(wvif);
-	return ret;
+	return wfx_set_mfp_ap(wvif);
 }
 
 void wfx_stop_ap(struct ieee80211_hw *hw, struct ieee80211_vif *vif,