From: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Date: Fri, 13 Jul 2018 13:24:38 +0900
Subject: tun: Fix use-after-free on XDP_TX
Patch-mainline: v4.18-rc6
Git-commit: 6e8cfd6d9d8049e2fd5b2de8a328519dc58ea1e6
References: bsc#1109837

On XDP_TX we need to free up the frame only when tun_xdp_tx() returns a
negative value. A positive value indicates that the packet is
successfully enqueued to the ptr_ring, so freeing the page causes
use-after-free.

Fixes: 735fc4054b3a ("xdp: change ndo_xdp_xmit API to support bulking")
Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/tun.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1685,7 +1685,7 @@ static struct sk_buff *tun_build_skb(str
 		case XDP_TX:
 			get_page(alloc_frag->page);
 			alloc_frag->offset += buflen;
-			if (tun_xdp_tx(tun->dev, &xdp))
+			if (tun_xdp_tx(tun->dev, &xdp) < 0)
 				goto err_redirect;
 			rcu_read_unlock();
 			local_bh_enable();