net/sched: act_vlan: Push skb->data to mac_header prior calling skb_vlan_*() functions

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@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Pravin Shelar <pshelar@ovn.org>
Cc: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/act_vlan.c b/net/sched/act_vlan.c
index a95c00b119da2c79a9a47fbf6bf341cf0582fda1..b57fcbcefea1d2ae4750c8f6dc2156f5d554f8f1 100644 (file)
--- a/net/sched/act_vlan.c
+++ b/net/sched/act_vlan.c
@@ -37,6 +37,12 @@ static int tcf_vlan(struct sk_buff *skb, const struct tc_action *a,
        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);
@@ -83,6 +89,9 @@ 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;
 }