[PATCH -next 2/2] netfilter: nfnetlink_queue: only add CAP_LEN attr when needed

[Florian Westphal <fw@strlen.de>]

CAP_LEN contains the size of the network packet we're queueing to
userspace, i.e. normally it is the same as the NFQA_PAYLOAD attribute len.

Include it only in the unlikely case when NFQA_PAYLOAD is truncated due
to copy_range limitations.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 Tested with examples/nf-queue.c from libnfqueue, it still
 prints 'truncated packet' on 1st packet sent from tracepath.

diff --git a/net/netfilter/nfnetlink_queue_core.c b/net/netfilter/nfnetlink_queue_core.c
index 3c42181..eb2cde8 100644
--- a/net/netfilter/nfnetlink_queue_core.c
+++ b/net/netfilter/nfnetlink_queue_core.c
@@ -472,7 +472,8 @@ nfqnl_build_packet_message(struct nfqnl_instance *queue,
 	if (ct && nfqnl_ct_put(skb, ct, ctinfo) < 0)
 		goto nla_put_failure;
 
-	if (cap_len > 0 && nla_put_be32(skb, NFQA_CAP_LEN, htonl(cap_len)))
+	if (cap_len > data_len &&
+	    nla_put_be32(skb, NFQA_CAP_LEN, htonl(cap_len)))
 		goto nla_put_failure;
 
 	if (nfqnl_put_packet_info(skb, entskb))
-- 
1.7.8.6