mac80211: fix a crash in ieee80211_beacon_get_tim on change_interface

Some drivers (e.g. ath9k) do not always disable beacons when they're
supposed to. When an interface is changed using the change_interface op,
the mode specific sdata part is in an undefined state and trying to
get a beacon at this point can produce weird crashes.

To fix this, add a check for ieee80211_sdata_running before using
anything from the sdata.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 5950e3abead9..b64b42bc774b 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -2230,6 +2230,9 @@ struct sk_buff *ieee80211_beacon_get_tim(struct ieee80211_hw *hw,
 
         sdata = vif_to_sdata(vif);
 
+        if (!ieee80211_sdata_running(sdata))
+                goto out;
+
         if (tim_offset)
                 *tim_offset = 0;
         if (tim_length)