net: fix socket refcounting in skb_complete_wifi_ack()

[ Upstream commit dd4f10722aeb10f4f582948839f066bebe44e5fb ]

TX skbs do not necessarily hold a reference on skb->sk->sk_refcnt
By the time TX completion happens, sk_refcnt might be already 0.

sock_hold()/sock_put() would then corrupt critical state, like
sk_wmem_alloc.

Fixes: bf7fa551e0ce ("mac80211: Resolve sk_refcnt/sk_wmem_alloc issue in wifi ack path")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 8 insertions, 7 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 1e3e0087245b..b806677f9fd3 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3871,7 +3871,7 @@ void skb_complete_wifi_ack(struct sk_buff *skb, bool acked)
 {
         struct sock *sk = skb->sk;
         struct sock_exterr_skb *serr;
-        int err;
+        int err = 1;
 
         skb->wifi_acked_valid = 1;
         skb->wifi_acked = acked;
@@ -3881,14 +3881,15 @@ 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);
+        /* Take a reference to prevent skb_orphan() from freeing the socket,
+         * but only if the socket refcount is not zero.
+         */
+        if (likely(atomic_inc_not_zero(&sk->sk_refcnt))) {
+                err = sock_queue_err_skb(sk, skb);
+                sock_put(sk);
+        }
         if (err)
                 kfree_skb(skb);
-
-        sock_put(sk);
 }
 EXPORT_SYMBOL_GPL(skb_complete_wifi_ack);