mac80211: fix warning in 6 GHz IE addition in mesh mode

The commit 24a2042c ("mac80211: add HE 6 GHz Band Capability
element") failed to check device capability before adding HE 6 GHz
capability element. Below warning is reported in 11ac device in mesh.
Fix that by checking device capability at HE 6 GHz cap IE addition
in mesh beacon and association request.

WARNING: CPU: 1 PID: 1897 at net/mac80211/util.c:2878
ieee80211_ie_build_he_6ghz_cap+0x149/0x150 [mac80211]
[ 3138.720358] Call Trace:
[ 3138.720361]  ieee80211_mesh_build_beacon+0x462/0x530 [mac80211]
[ 3138.720363]  ieee80211_start_mesh+0xa8/0xf0 [mac80211]
[ 3138.720365]  __cfg80211_join_mesh+0x122/0x3e0 [cfg80211]
[ 3138.720368]  nl80211_join_mesh+0x3d3/0x510 [cfg80211]

Fixes: 24a2042c ("mac80211: add HE 6 GHz Band Capability element")
Reported-by: Markus Theil <markus.theil@tu-ilmenau.de>
Signed-off-by: Rajkumar Manoharan <rmanohar@codeaurora.org>
Link: https://lore.kernel.org/r/1593656424-18240-1-git-send-email-rmanohar@codeaurora.orgSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mesh.c

@@ -617,6 +617,19 @@ int mesh_add_he_oper_ie(struct ieee80211_sub_if_data *sdata,
 int mesh_add_he_6ghz_cap_ie(struct ieee80211_sub_if_data *sdata,
 			    struct sk_buff *skb)
 {
+	struct ieee80211_supported_band *sband;
+	const struct ieee80211_sband_iftype_data *iftd;
+
+	sband = ieee80211_get_sband(sdata);
+	if (!sband)
+		return -EINVAL;
+
+	iftd = ieee80211_get_sband_iftype_data(sband,
+					       NL80211_IFTYPE_MESH_POINT);
+	/* The device doesn't support HE in mesh mode or at all */
+	if (!iftd)
+		return 0;
+
 	ieee80211_ie_build_he_6ghz_cap(sdata, skb);
 	return 0;
 }

net/mac80211/util.c

@@ -2878,6 +2878,10 @@ void ieee80211_ie_build_he_6ghz_cap(struct ieee80211_sub_if_data *sdata,
 	if (WARN_ON(!iftd))
 		return;
 
+	/* Check for device HE 6 GHz capability before adding element */
+	if (!iftd->he_6ghz_capa.capa)
+		return;
+
 	cap = le16_to_cpu(iftd->he_6ghz_capa.capa);
 	cap &= ~IEEE80211_HE_6GHZ_CAP_SM_PS;