mac80211: Fix possible sband related NULL pointer de-reference


[ Upstream commit 21a8e9dd52b64f0170bad208293ef8c30c3c1403 ]

Existing API 'ieee80211_get_sdata_band' returns default 2 GHz band even
if the channel context configuration is NULL. This crashes for chipsets
which support 5 Ghz alone when it tries to access members of 'sband'.
Channel context configuration can be NULL in multivif case and when
channel switch is in progress (or) when it fails. Fix this by replacing
the API 'ieee80211_get_sdata_band' with  'ieee80211_get_sband' which
returns a NULL pointer for sband when the channel configuration is NULL.

An example scenario is as below:

In multivif mode (AP + STA) with drivers like ath10k, when we do a
channel switch in the AP vif (which has a number of clients connected)
and a STA vif which is connected to some other AP, when the channel
switch in AP vif fails, while the STA vifs tries to connect to the
other AP, there is a window where the channel context is NULL/invalid
and this results in a crash  while the clients connected to the AP vif
tries to reconnect and this race is very similar to the one investigated
by Michal in https://patchwork.kernel.org/patch/3788161/ and this does
happens with hardware that supports 5Ghz alone after long hours of
testing with continuous channel switch on the AP vif

ieee80211 phy0: channel context reservation cannot be finalized because
some interfaces aren't switching
wlan0: failed to finalize CSA, disconnecting
wlan0-1: deauthenticating from 8c:fd:f0:01:54:9c by local choice
	(Reason: 3=DEAUTH_LEAVING)

	WARNING: CPU: 1 PID: 19032 at net/mac80211/ieee80211_i.h:1013 sta_info_alloc+0x374/0x3fc [mac80211]
	[<bf77272c>] (sta_info_alloc [mac80211])
	[<bf78776c>] (ieee80211_add_station [mac80211]))
	[<bf73cc50>] (nl80211_new_station [cfg80211])

	Unable to handle kernel NULL pointer dereference at virtual
	address 00000014
	pgd = d5f4c000
	Internal error: Oops: 17 [#1] PREEMPT SMP ARM
	PC is at sta_info_alloc+0x380/0x3fc [mac80211]
	LR is at sta_info_alloc+0x37c/0x3fc [mac80211]
	[<bf772738>] (sta_info_alloc [mac80211])
	[<bf78776c>] (ieee80211_add_station [mac80211])
	[<bf73cc50>] (nl80211_new_station [cfg80211]))

Cc: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 03dbc6b..7fd544d 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -991,21 +991,6 @@
 	lockdep_assert_held(&sdata->wdev.mtx);
 }
 
-static inline enum nl80211_band
-ieee80211_get_sdata_band(struct ieee80211_sub_if_data *sdata)
-{
-	enum nl80211_band band = NL80211_BAND_2GHZ;
-	struct ieee80211_chanctx_conf *chanctx_conf;
-
-	rcu_read_lock();
-	chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf);
-	if (!WARN_ON(!chanctx_conf))
-		band = chanctx_conf->def.chan->band;
-	rcu_read_unlock();
-
-	return band;
-}
-
 static inline int
 ieee80211_chandef_get_shift(struct cfg80211_chan_def *chandef)
 {
@@ -1410,6 +1395,27 @@
 	return container_of(wdev, struct ieee80211_sub_if_data, wdev);
 }
 
+static inline struct ieee80211_supported_band *
+ieee80211_get_sband(struct ieee80211_sub_if_data *sdata)
+{
+	struct ieee80211_local *local = sdata->local;
+	struct ieee80211_chanctx_conf *chanctx_conf;
+	enum nl80211_band band;
+
+	rcu_read_lock();
+	chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf);
+
+	if (WARN_ON(!chanctx_conf)) {
+		rcu_read_unlock();
+		return NULL;
+	}
+
+	band = chanctx_conf->def.chan->band;
+	rcu_read_unlock();
+
+	return local->hw.wiphy->bands[band];
+}
+
 /* this struct represents 802.11n's RA/TID combination */
 struct ieee80211_ra_tid {
 	u8 ra[ETH_ALEN];