linux-kernel - [PATCH 4.8 03/35] net/sched: act_vlan: Push skb->data to mac_header prior calling skb_vlan

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Date:   Sun, 13 Nov 2016 12:27:17 +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,
        Shmulik Ladkani <shmulik.ladkani@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Pravin Shelar <pshelar@....org>,
        Jiri Pirko <jiri@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.8 03/35] net/sched: act_vlan: Push skb->data to mac_header prior calling skb_vlan_*() functions

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

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

From: Shmulik Ladkani <shmulik.ladkani@...il.com>


[ Upstream commit f39acc84aad10710e89835c60d3b6694c43a8dd9 ]

Generic skb_vlan_push/skb_vlan_pop functions don't properly handle the
case where the input skb data pointer does not point at the mac header:

- They're doing push/pop, but fail to properly unwind data back to its
  original location.
  For example, in the skb_vlan_push case, any subsequent
  'skb_push(skb, skb->mac_len)' calls make the skb->data point 4 bytes
  BEFORE start of frame, leading to bogus frames that may be transmitted.

- They update rcsum per the added/removed 4 bytes tag.
  Alas if data is originally after the vlan/eth headers, then these
  bytes were already pulled out of the csum.

OTOH calling skb_vlan_push/skb_vlan_pop with skb->data at mac_header
present no issues.

act_vlan is the only caller to skb_vlan_*() that has skb->data pointing
at network header (upon ingress).
Other calles (ovs, bpf) already adjust skb->data at mac_header.

This patch fixes act_vlan to point to the mac_header prior calling
skb_vlan_*() functions, as other callers do.

Signed-off-by: Shmulik Ladkani <shmulik.ladkani@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: Pravin Shelar <pshelar@....org>
Cc: Jiri Pirko <jiri@...lanox.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/sched/act_vlan.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/net/sched/act_vlan.c
+++ b/net/sched/act_vlan.c
@@ -36,6 +36,12 @@ static int tcf_vlan(struct sk_buff *skb,
 	bstats_update(&v->tcf_bstats, skb);
 	action = v->tcf_action;
 
+	/* Ensure 'data' points at mac_header prior calling vlan manipulating
+	 * functions.
+	 */
+	if (skb_at_tc_ingress(skb))
+		skb_push_rcsum(skb, skb->mac_len);
+
 	switch (v->tcfv_action) {
 	case TCA_VLAN_ACT_POP:
 		err = skb_vlan_pop(skb);
@@ -57,6 +63,9 @@ drop:
 	action = TC_ACT_SHOT;
 	v->tcf_qstats.drops++;
 unlock:
+	if (skb_at_tc_ingress(skb))
+		skb_pull_rcsum(skb, skb->mac_len);
+
 	spin_unlock(&v->tcf_lock);
 	return action;
 }