[PATCH] wifi: mac80211: use two-phase skb reclamation in ieee80211_do_stop()

[Dmitry Antipov <dmantipov@xxxxxxxxx>]

Since '__dev_queue_xmit()' should be called with interrupts enabled,
the following backtrace:

ieee80211_do_stop()
 ...
 spin_lock_irqsave(&local->queue_stop_reason_lock, flags)
 ...
 ieee80211_free_txskb()
  ieee80211_report_used_skb()
   ieee80211_report_ack_skb()
    cfg80211_mgmt_tx_status_ext()
     nl80211_frame_tx_status()
      genlmsg_multicast_netns()
       genlmsg_multicast_netns_filtered()
        nlmsg_multicast_filtered()
	 netlink_broadcast_filtered()
	  do_one_broadcast()
	   netlink_broadcast_deliver()
	    __netlink_sendskb()
	     netlink_deliver_tap()
	      __netlink_deliver_tap_skb()
	       dev_queue_xmit()
	        __dev_queue_xmit() ; with IRQS disabled
 ...
 spin_unlock_irqrestore(&local->queue_stop_reason_lock, flags)

issues the warning (as reported by syzbot reproducer):

WARNING: CPU: 2 PID: 5128 at kernel/softirq.c:362 __local_bh_enable_ip+0xc3/0x120

Fix this by implementing a two-phase skb reclamation in
'ieee80211_do_stop()', where actual work is performed
outside of a section with interrupts disabled.

Fixes: 5061b0c2b906 ("mac80211: cooperate more with network namespaces")
Reported-by: syzbot+1a3986bbd3169c307819@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=1a3986bbd3169c307819
Signed-off-by: Dmitry Antipov <dmantipov@xxxxxxxxx>
---
 net/mac80211/iface.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index b4ad66af3af3..f735e41560a3 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -462,6 +462,7 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata, bool going_do
 {
 	struct ieee80211_local *local = sdata->local;
 	unsigned long flags;
+	struct sk_buff_head freeq;
 	struct sk_buff *skb, *tmp;
 	u32 hw_reconf_flags = 0;
 	int i, flushed;
@@ -637,18 +638,32 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata, bool going_do
 		skb_queue_purge(&sdata->status_queue);
 	}
 
+	/*
+	 * Since ieee80211_free_txskb() may issue __dev_queue_xmit()
+	 * which should be called with interrupts enabled, reclamation
+	 * is done in two phases:
+	 */
+	__skb_queue_head_init(&freeq);
+
+	/* unlink from local queues... */
 	spin_lock_irqsave(&local->queue_stop_reason_lock, flags);
 	for (i = 0; i < IEEE80211_MAX_QUEUES; i++) {
 		skb_queue_walk_safe(&local->pending[i], skb, tmp) {
 			struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 			if (info->control.vif == &sdata->vif) {
 				__skb_unlink(skb, &local->pending[i]);
-				ieee80211_free_txskb(&local->hw, skb);
+				__skb_queue_tail(&freeq, skb);
 			}
 		}
 	}
 	spin_unlock_irqrestore(&local->queue_stop_reason_lock, flags);
 
+	/* ... and perform actual reclamation with interrupts enabled. */
+	skb_queue_walk_safe(&freeq, skb, tmp) {
+		__skb_unlink(skb, &freeq);
+		ieee80211_free_txskb(&local->hw, skb);
+	}
+
 	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
 		ieee80211_txq_remove_vlan(local, sdata);
 
-- 
2.46.0