[PATCH net] openvswitch: fix panic with multiple vlan headers

[Jiri Benc <jbenc-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

When there are multiple vlan headers present in a received frame, the first
one is put into vlan_tci and protocol is set to ETH_P_8021Q. Anything in the
skb beyond the VLAN TPID may be still non-linear, including the inner TCI
and ethertype. While ovs_flow_extract takes care of IP and IPv6 headers, it
does nothing with ETH_P_8021Q. Later, if OVS_ACTION_ATTR_POP_VLAN is
executed, __pop_vlan_tci pulls the next vlan header into vlan_tci.

This leads to two things:

1. Part of the resulting ethernet header is in the non-linear part of the
   skb. When eth_type_trans is called later as the result of
   OVS_ACTION_ATTR_OUTPUT, kernel BUGs in __skb_pull. Also, __pop_vlan_tci
   is in fact accessing random data when it reads past the TPID.

2. network_header points into the ethernet header instead of behind it.
   mac_len is set to a wrong value (10), too.

Reported-by: Yulong Pei <ypei-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Jiri Benc <jbenc-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 net/openvswitch/actions.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index fe5cda0deb39..5231652a95d9 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -42,6 +42,9 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 
 static int make_writable(struct sk_buff *skb, int write_len)
 {
+	if (!pskb_may_pull(skb, write_len))
+		return -ENOMEM;
+
 	if (!skb_cloned(skb) || skb_clone_writable(skb, write_len))
 		return 0;
 
@@ -70,6 +73,8 @@ static int __pop_vlan_tci(struct sk_buff *skb, __be16 *current_tci)
 
 	vlan_set_encap_proto(skb, vhdr);
 	skb->mac_header += VLAN_HLEN;
+	if (skb_network_offset(skb) < ETH_HLEN)
+		skb_set_network_header(skb, ETH_HLEN);
 	skb_reset_mac_len(skb);
 
 	return 0;
-- 
1.8.3.1