[PATCH -next] 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 length.

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>
---
 net/netfilter/nfnetlink_queue_core.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

 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 cff4449..49c149b 100644
--- a/net/netfilter/nfnetlink_queue_core.c
+++ b/net/netfilter/nfnetlink_queue_core.c
@@ -40,6 +40,7 @@
 #endif
 
 #define NFQNL_QMAX_DEFAULT 1024
+#define NFQNL_MAX_COPY_RANGE (0xffff - NLA_HDRLEN)
 
 struct nfqnl_instance {
 	struct hlist_node hlist;		/* global list of queues */
@@ -122,7 +123,7 @@ instance_create(struct nfnl_queue_net *q, u_int16_t queue_num,
 	inst->queue_num = queue_num;
 	inst->peer_portid = portid;
 	inst->queue_maxlen = NFQNL_QMAX_DEFAULT;
-	inst->copy_range = 0xffff;
+	inst->copy_range = NFQNL_MAX_COPY_RANGE;
 	inst->copy_mode = NFQNL_COPY_NONE;
 	spin_lock_init(&inst->lock);
 	INIT_LIST_HEAD(&inst->queue_list);
@@ -333,10 +334,9 @@ nfqnl_build_packet_message(struct nfqnl_instance *queue,
 			return NULL;
 
 		data_len = ACCESS_ONCE(queue->copy_range);
-		if (data_len == 0 || data_len > entskb->len)
+		if (data_len > entskb->len)
 			data_len = entskb->len;
 
-
 		if (!entskb->head_frag ||
 		    skb_headlen(entskb) < L1_CACHE_BYTES ||
 		    skb_shinfo(entskb)->nr_frags >= MAX_SKB_FRAGS)
@@ -465,7 +465,8 @@ 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))
@@ -732,8 +733,8 @@ nfqnl_set_mode(struct nfqnl_instance *queue,
 		 * length that we support is 65531 bytes. We send truncated
 		 * packets if the specified length is larger than that.
 		 */
-		if (range > 0xffff - NLA_HDRLEN)
-			queue->copy_range = 0xffff - NLA_HDRLEN;
+		if (range == 0 || range > NFQNL_MAX_COPY_RANGE)
+			queue->copy_range = NFQNL_MAX_COPY_RANGE;
 		else
 			queue->copy_range = range;
 		break;
-- 
1.8.1.5