net, ipv4, ipv6: Correct assignment of skb->network_header to skb->tail

This corrects an regression introduced by "net: Use 16bits for *_headers
fields of struct skbuff" when NET_SKBUFF_DATA_USES_OFFSET is not set. In
that case skb->tail will be a pointer however skb->network_header is now
an offset.

This patch corrects the problem by adding a wrapper to return skb tail as
an offset regardless of the value of NET_SKBUFF_DATA_USES_OFFSET. It seems
that skb->tail that this offset may be more than 64k and some care has been
taken to treat such cases as an error.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 1 deletions

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 37deedd48bcc..688517c7ff17 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -676,6 +676,8 @@ static void netpoll_neigh_reply(struct sk_buff *skb, struct netpoll_info *npinfo
 
 		spin_lock_irqsave(&npinfo->rx_lock, flags);
 		list_for_each_entry_safe(np, tmp, &npinfo->rx_np, rx) {
+			unsigned long tail_offset;
+
 			if (!ipv6_addr_equal(daddr, &np->local_ip.in6))
 				continue;
 
@@ -700,7 +702,12 @@ static void netpoll_neigh_reply(struct sk_buff *skb, struct netpoll_info *npinfo
 			hdr->saddr = *saddr;
 			hdr->daddr = *daddr;
 
-			send_skb->transport_header = send_skb->tail;
+			tail_offset = skb_tail_offset(skb);
+			if (tail_offset > 0xffff) {
+				kfree_skb(send_skb);
+				continue;
+			}
+			skb_set_network_header(send_skb, tail_offset);
 			skb_put(send_skb, size);
 
 			icmp6h = (struct icmp6hdr *)skb_transport_header(skb);