netdev - [PATCH net] tap: call skb_probe_transport

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Message-Id: <20181230222105.36031-1-willemdebruijn.kernel@gmail.com>
Date:   Sun, 30 Dec 2018 17:21:05 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, idosch@...sch.org, borntraeger@...ibm.com,
        Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net] tap: call skb_probe_transport_header after setting skb->dev

From: Willem de Bruijn <willemb@...gle.com>

The BPF flow dissector expects either skb->sk or skb->dev set on
all skbs. Delay flow dissection until after skb->dev is set.

This requires calling from within an rcu read-side critical section.
That is fine, see also the call from tun_xdp_one.

Fixes: d0e13a1488ad ("flow_dissector: lookup netns by skb->sk if skb->dev is NULL")
Reported-by: Christian Borntraeger <borntraeger@...ibm.com>
Signed-off-by: Willem de Bruijn <willemb@...gle.com>
---
 drivers/net/tap.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 443b2694130c..c0b52e48f0e6 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -1177,8 +1177,6 @@ static int tap_get_user_xdp(struct tap_queue *q, struct xdp_buff *xdp)
 			goto err_kfree;
 	}
 
-	skb_probe_transport_header(skb, ETH_HLEN);
-
 	/* Move network header to the right position for VLAN tagged packets */
 	if ((skb->protocol == htons(ETH_P_8021Q) ||
 	     skb->protocol == htons(ETH_P_8021AD)) &&
@@ -1189,6 +1187,7 @@ static int tap_get_user_xdp(struct tap_queue *q, struct xdp_buff *xdp)
 	tap = rcu_dereference(q->tap);
 	if (tap) {
 		skb->dev = tap->dev;
+		skb_probe_transport_header(skb, ETH_HLEN);
 		dev_queue_xmit(skb);
 	} else {
 		kfree_skb(skb);
-- 
2.20.1.415.g653613c723-goog