[PATCH v3 2/3] Do error handling if __build_packet_message fails

[Marcelo Ricardo Leitner <mleitner@redhat.com>]

Currently, we don't check if __build_packet_message fails or not and
that leaves it prone to sending incomplete messages to userspace.

This commit fixes it by canceling the new message if there was any issue
while building it and makes sure the skb is freed if it was the only
messsage in it.

Signed-off-by: Marcelo Ricardo Leitner <mleitner@redhat.com>
---
 net/netfilter/nfnetlink_log.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
index b1e3a05794169283ed50d1c0fb4f44d9e7753eeb..05184a3d860885c10c3e977fdc47fb86e3528afa 100644
--- a/net/netfilter/nfnetlink_log.c
+++ b/net/netfilter/nfnetlink_log.c
@@ -568,10 +568,8 @@ __build_packet_message(struct nfnl_log_net *log,
 		struct nlattr *nla;
 		int size = nla_attr_size(data_len);
 
-		if (skb_tailroom(inst->skb) < nla_total_size(data_len)) {
-			printk(KERN_WARNING "nfnetlink_log: no tailroom!\n");
-			return -1;
-		}
+		if (skb_tailroom(inst->skb) < nla_total_size(data_len))
+			goto nla_put_failure;
 
 		nla = (struct nlattr *)skb_put(inst->skb, nla_total_size(data_len));
 		nla->nla_type = NFULA_PAYLOAD;
@@ -586,6 +584,7 @@ __build_packet_message(struct nfnl_log_net *log,
 
 nla_put_failure:
 	PRINTR(KERN_ERR "nfnetlink_log: error creating log nlmsg\n");
+	nlmsg_cancel(skb, nlh);
 	return -1;
 }
 
@@ -708,8 +707,9 @@ nfulnl_log_packet(struct net *net,
 
 	inst->qlen++;
 
-	__build_packet_message(log, inst, skb, data_len, pf,
-				hooknum, in, out, prefix, plen);
+	if (__build_packet_message(log, inst, skb, data_len, pf,
+				hooknum, in, out, prefix, plen))
+		goto build_failure;
 
 	if (inst->qlen >= qthreshold)
 		__nfulnl_flush(inst);
@@ -726,6 +726,15 @@ unlock_and_release:
 	instance_put(inst);
 	return;
 
+build_failure:
+	/* If no other messages in it, we're good to free it. */
+	if (!inst->skb->len) {
+		kfree_skb(inst->skb);
+		inst->skb = NULL;
+	}
+
+	inst->qlen--;
+
 alloc_failure:
 	/* FIXME: statistics */
 	goto unlock_and_release;
-- 
1.9.3