linux-kernel - [PATCH 4.20 005/145] tap: call skb_probe_transport

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Date:   Mon,  7 Jan 2019 13:30:42 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Willem de Bruijn <willemb@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.20 005/145] tap: call skb_probe_transport_header after setting skb->dev

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

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

[ Upstream commit 8c76e77f9069f10505c08e02646c3ee11ad79038 ]

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>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/tap.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -1177,8 +1177,6 @@ static int tap_get_user_xdp(struct tap_q
 			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_q
 	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);