Re: [PATCH net-next v4] vxlan: fix ND proxy when skb doesn't have transport header offset

[David Miller]

From: Vincent Bernat 
Date: Sun,  2 Apr 2017 11:00:06 +0200

> When an incoming frame is tagged or when GRO is disabled, the skb
> handled to vxlan_xmit() doesn't contain a valid transport header
> offset. This makes ND proxying fail.
> 
> We combine two changes: replace use of skb_transport_offset() and ensure
> the necessary amount of skb is linear just before using it:
> 
>  - In vxlan_xmit(), when determining if we have an ICMPv6 neighbor
>discovery packet, just check if it is an ICMPv6 packet and rely on
>neigh_reduce() to do more checks if this is the case. The use of
>pskb_may_pull() is replaced by skb_header_pointer() for just the IPv6
>header.
> 
>  - In neigh_reduce(), add pskb_may_pull() for IPv6 header and neighbor
>discovery message since this was removed from vxlan_xmit(). Replace
>skb_transport_header() with ipv6_hdr() + 1.
> 
>  - In vxlan_na_create(), replace first skb_transport_offset() with
>ipv6_hdr() + 1 and second with skb_network_offset() + sizeof(struct
>ipv6hdr). Additionally, ensure we pskb_may_pull() the whole skb as we
>need it to iterate over the options.
> 
> Signed-off-by: Vincent Bernat 

Applied, thanks.

[PATCH net-next v4] vxlan: fix ND proxy when skb doesn't have transport header offset

[Vincent Bernat]

When an incoming frame is tagged or when GRO is disabled, the skb
handled to vxlan_xmit() doesn't contain a valid transport header
offset. This makes ND proxying fail.

We combine two changes: replace use of skb_transport_offset() and ensure
the necessary amount of skb is linear just before using it:

 - In vxlan_xmit(), when determining if we have an ICMPv6 neighbor
   discovery packet, just check if it is an ICMPv6 packet and rely on
   neigh_reduce() to do more checks if this is the case. The use of
   pskb_may_pull() is replaced by skb_header_pointer() for just the IPv6
   header.

 - In neigh_reduce(), add pskb_may_pull() for IPv6 header and neighbor
   discovery message since this was removed from vxlan_xmit(). Replace
   skb_transport_header() with ipv6_hdr() + 1.

 - In vxlan_na_create(), replace first skb_transport_offset() with
   ipv6_hdr() + 1 and second with skb_network_offset() + sizeof(struct
   ipv6hdr). Additionally, ensure we pskb_may_pull() the whole skb as we
   need it to iterate over the options.

Signed-off-by: Vincent Bernat 
---
 drivers/net/vxlan.c | 29 +++--
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 1e54fb5c883a..89cb8267 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -1515,7 +1515,7 @@ static struct sk_buff *vxlan_na_create(struct sk_buff 
*request,
int ns_olen;
int i, len;
 
-   if (dev == NULL)
+   if (dev == NULL || !pskb_may_pull(request, request->len))
return NULL;
 
len = LL_RESERVED_SPACE(dev) + sizeof(struct ipv6hdr) +
@@ -1530,10 +1530,11 @@ static struct sk_buff *vxlan_na_create(struct sk_buff 
*request,
skb_push(reply, sizeof(struct ethhdr));
skb_reset_mac_header(reply);
 
-   ns = (struct nd_msg *)skb_transport_header(request);
+   ns = (struct nd_msg *)(ipv6_hdr(request) + 1);
 
daddr = eth_hdr(request)->h_source;
-   ns_olen = request->len - skb_transport_offset(request) - sizeof(*ns);
+   ns_olen = request->len - skb_network_offset(request) -
+   sizeof(struct ipv6hdr) - sizeof(*ns);
for (i = 0; i < ns_olen-1; i += (ns->opt[i+1]<<3)) {
if (ns->opt[i] == ND_OPT_SOURCE_LL_ADDR) {
daddr = ns->opt + i + sizeof(struct nd_opt_hdr);
@@ -1604,10 +1605,13 @@ static int neigh_reduce(struct net_device *dev, struct 
sk_buff *skb, __be32 vni)
if (!in6_dev)
goto out;
 
+   if (!pskb_may_pull(skb, sizeof(struct ipv6hdr) + sizeof(struct nd_msg)))
+   goto out;
+
iphdr = ipv6_hdr(skb);
daddr = >daddr;
 
-   msg = (struct nd_msg *)skb_transport_header(skb);
+   msg = (struct nd_msg *)(iphdr + 1);
if (msg->icmph.icmp6_code != 0 ||
msg->icmph.icmp6_type != NDISC_NEIGHBOUR_SOLICITATION)
goto out;
@@ -2242,16 +2246,13 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, 
struct net_device *dev)
if (ntohs(eth->h_proto) == ETH_P_ARP)
return arp_reduce(dev, skb, vni);
 #if IS_ENABLED(CONFIG_IPV6)
-   else if (ntohs(eth->h_proto) == ETH_P_IPV6 &&
-pskb_may_pull(skb, sizeof(struct ipv6hdr)
-  + sizeof(struct nd_msg)) &&
-ipv6_hdr(skb)->nexthdr == IPPROTO_ICMPV6) {
-   struct nd_msg *msg;
-
-   msg = (struct nd_msg 
*)skb_transport_header(skb);
-   if (msg->icmph.icmp6_code == 0 &&
-   msg->icmph.icmp6_type == 
NDISC_NEIGHBOUR_SOLICITATION)
-   return neigh_reduce(dev, skb, vni);
+   else if (ntohs(eth->h_proto) == ETH_P_IPV6) {
+   struct ipv6hdr *hdr, _hdr;
+   if ((hdr = skb_header_pointer(skb,
+ skb_network_offset(skb),
+ sizeof(_hdr), &_hdr)) &&
+   hdr->nexthdr == IPPROTO_ICMPV6)
+   return neigh_reduce(dev, skb, vni);
}
 #endif
}
-- 
2.11.0