wifi: mac80211: avoid double free in auth/assoc timeout

In case of authentication/association timeout (as detected in
ieee80211_iface_work->ieee80211_sta_work), ieee80211_destroy_auth_data
is called.
At the beginning of it, the pointer to ifmgd::auth_data memory is
copied to a local variable.
If iface_work is queued again during the execution of the current one,
and then the driver is flushing the wiphy_works (for its needs),
ieee80211_destroy_auth_data will run again and free auth_data.
Then when the execution of the original worker continues, the previously
copied pointer will be freed, causing a kernel bug:
 kernel BUG at mm/slub.c:553! (double free)

Same for association timeout (just with ieee80211_destroy_assoc_data and
ifmgd::assoc_data)

Fix this by NULLifying auth/assoc data right after we copied
the pointer to it. That way, even in the scenario above, the code will
not handle the same timeout twice.

Signed-off-by: Miri Korenblit <[email protected]>
Reviewed-by: Johannes Berg <[email protected]>
Link: https://patch.msgid.link/20250102161730.0c3f7f781096.I2b458fb53291b06717077a815755288a81274756@changeid
Signed-off-by: Johannes Berg <[email protected]>

Author: Miriam-Rachel

net/mac80211/mlme.c

@@ -4402,6 +4402,8 @@ static void ieee80211_destroy_auth_data(struct ieee80211_sub_if_data *sdata,
 
 	lockdep_assert_wiphy(sdata->local->hw.wiphy);
 
+	sdata->u.mgd.auth_data = NULL;
+
 	if (!assoc) {
 		/*
 		 * we are not authenticated yet, the only timer that could be
@@ -4423,7 +4425,6 @@ static void ieee80211_destroy_auth_data(struct ieee80211_sub_if_data *sdata,
 
 	cfg80211_put_bss(sdata->local->hw.wiphy, auth_data->bss);
 	kfree(auth_data);
-	sdata->u.mgd.auth_data = NULL;
 }
 
 enum assoc_status {
@@ -4440,6 +4441,8 @@ static void ieee80211_destroy_assoc_data(struct ieee80211_sub_if_data *sdata,
 
 	lockdep_assert_wiphy(sdata->local->hw.wiphy);
 
+	sdata->u.mgd.assoc_data = NULL;
+
 	if (status != ASSOC_SUCCESS) {
 		/*
 		 * we are not associated yet, the only timer that could be
@@ -4478,7 +4481,6 @@ static void ieee80211_destroy_assoc_data(struct ieee80211_sub_if_data *sdata,
 	}
 
 	kfree(assoc_data);
-	sdata->u.mgd.assoc_data = NULL;
 }
 
 static void ieee80211_auth_challenge(struct ieee80211_sub_if_data *sdata,