linux-kernel - [PATCH 3.12 06/91] packet: do skb_probe_transport

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Message-Id: <be67618b17b931289b34c376926b8de338152fb3.1452015822.git.jslaby@suse.cz>
Date:	Tue,  5 Jan 2016 18:45:50 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Daniel Borkmann <daniel@...earbox.net>,
	"David S . Miller" <davem@...emloft.net>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 06/91] packet: do skb_probe_transport_header when we actually have data

From: Daniel Borkmann <daniel@...earbox.net>

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

===============

[ Upstream commit efdfa2f7848f64517008136fb41f53c4a1faf93a ]

In tpacket_fill_skb() commit c1aad275b029 ("packet: set transport
header before doing xmit") and later on 40893fd0fd4e ("net: switch
to use skb_probe_transport_header()") was probing for a transport
header on the skb from a ring buffer slot, but at a time, where
the skb has _not even_ been filled with data yet. So that call into
the flow dissector is pretty useless. Lets do it after we've set
up the skb frags.

Fixes: c1aad275b029 ("packet: set transport header before doing xmit")
Reported-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Jason Wang <jasowang@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 net/packet/af_packet.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 7f63613148b9..645010b9abc0 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1991,7 +1991,6 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
 
 	skb_reserve(skb, hlen);
 	skb_reset_network_header(skb);
-	skb_probe_transport_header(skb, 0);
 
 	if (po->tp_tx_has_off) {
 		int off_min, off_max, off;
@@ -2076,6 +2075,8 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
 		len = ((to_write > len_max) ? len_max : to_write);
 	}
 
+	skb_probe_transport_header(skb, 0);
+
 	return tp_len;
 }
 
-- 
2.6.4

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