netdev - [PATCH net] tun: Fix use-after-free on XDP

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Date:   Fri, 13 Jul 2018 13:24:38 +0900
From:   Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        netdev@...r.kernel.org, Jesper Dangaard Brouer <brouer@...hat.com>
Subject: [PATCH net] tun: Fix use-after-free on XDP_TX

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@....ntt.co.jp>
---
 drivers/net/tun.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index a192a01..f5727ba 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1688,7 +1688,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 		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();
-- 
1.8.3.1