Merge branch 'sock_queue_err_skb'

Alexander Duyck says:

====================
Address reference counting issues with sock_queue_err_skb

After looking over the code for skb_clone_sk after some comments made by
Eric Dumazet I have come to the conclusion that skb_clone_sk is taking the
correct approach in how to handle the sk_refcnt when creating a buffer that
is eventually meant to be returned to the socket via the sock_queue_err_skb
function.

However upon review of other callers I found what I believe to be a
possible reference count issue in the path for handling "wifi ack" packets.
To address this I have applied the same logic that is currently in place so
that the sk_refcnt will be forced to stay at least 1, or we will not
provide an skb to return in the sk_error_queue.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -3511,6 +3511,19 @@ struct sk_buff *sock_dequeue_err_skb(struct sock *sk)
 }
 EXPORT_SYMBOL(sock_dequeue_err_skb);
 
+/**
+ * skb_clone_sk - create clone of skb, and take reference to socket
+ * @skb: the skb to clone
+ *
+ * This function creates a clone of a buffer that holds a reference on
+ * sk_refcnt.  Buffers created via this function are meant to be
+ * returned using sock_queue_err_skb, or free via kfree_skb.
+ *
+ * When passing buffers allocated with this function to sock_queue_err_skb
+ * it is necessary to wrap the call with sock_hold/sock_put in order to
+ * prevent the socket from being released prior to being enqueued on
+ * the sk_error_queue.
+ */
 struct sk_buff *skb_clone_sk(struct sk_buff *skb)
 {
 	struct sock *sk = skb->sk;
@@ -3615,9 +3628,14 @@ void skb_complete_wifi_ack(struct sk_buff *skb, bool acked)
 	serr->ee.ee_errno = ENOMSG;
 	serr->ee.ee_origin = SO_EE_ORIGIN_TXSTATUS;
 
+	/* take a reference to prevent skb_orphan() from freeing the socket */
+	sock_hold(sk);
+
 	err = sock_queue_err_skb(sk, skb);
 	if (err)
 		kfree_skb(skb);
+
+	sock_put(sk);
 }
 EXPORT_SYMBOL_GPL(skb_complete_wifi_ack);
 

net/mac80211/tx.c

@@ -2072,30 +2072,23 @@ netdev_tx_t ieee80211_subif_start_xmit(struct sk_buff *skb,
 
 	if (unlikely(!multicast && skb->sk &&
 		     skb_shinfo(skb)->tx_flags & SKBTX_WIFI_STATUS)) {
-		struct sk_buff *orig_skb = skb;
+		struct sk_buff *ack_skb = skb_clone_sk(skb);
 
-		skb = skb_clone(skb, GFP_ATOMIC);
-		if (skb) {
+		if (ack_skb) {
 			unsigned long flags;
 			int id;
 
 			spin_lock_irqsave(&local->ack_status_lock, flags);
-			id = idr_alloc(&local->ack_status_frames, orig_skb,
+			id = idr_alloc(&local->ack_status_frames, ack_skb,
 				       1, 0x10000, GFP_ATOMIC);
 			spin_unlock_irqrestore(&local->ack_status_lock, flags);
 
 			if (id >= 0) {
 				info_id = id;
 				info_flags |= IEEE80211_TX_CTL_REQ_TX_STATUS;
-			} else if (skb_shared(skb)) {
-				kfree_skb(orig_skb);
 			} else {
-				kfree_skb(skb);
-				skb = orig_skb;
+				kfree_skb(ack_skb);
 			}
-		} else {
-			/* couldn't clone -- lose tx status ... */
-			skb = orig_skb;
 		}
 	}