From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Fri, 26 Jan 2018 01:36:31 +0200
Subject: tap: fix use-after-free
Patch-mainline: v4.16-rc1
Git-commit: 88fae87327a2261cf8db078f6ce4e5a3e55b30b1
References: bsc#1076830

Lockless access to __ptr_ring_full is only legal if ring is
never resized, otherwise it might cause use-after free errors.
Simply drop the lockless test, we'll drop the packet
a bit later when produce fails.

Fixes: 362899b8 ("macvtap: switch to use skb array")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

---
 drivers/net/tap.c |    3 ---
 1 file changed, 3 deletions(-)

--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -330,9 +330,6 @@ rx_handler_result_t tap_handle_frame(str
 	if (!q)
 		return RX_HANDLER_PASS;
 
-	if (__ptr_ring_full(&q->ring))
-		goto drop;
-
 	skb_push(skb, ETH_HLEN);
 
 	/* Apply the forward feature mask so that we perform segmentation