On Tue, May 03, 2016 at 08:12:50PM +0200, Pablo Neira Ayuso wrote:

On Thu, Apr 28, 2016 at 07:13:44PM +0200, Florian Westphal wrote:

quoted

The iteration process is lockless, so we test if the conntrack object is
eligible for printing (e.g. is AF_INET) after obtaining the reference
count.

Once we put all conntracks into same hash table we might see more
entries that need to be skipped.

So add a helper and first perform the test in a lockless fashion
for fast skip.

Once we obtain the reference count, just repeat the check.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 .../netfilter/nf_conntrack_l3proto_ipv4_compat.c   | 24 +++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c
index f0dfe92..483cf79 100644
--- a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c
+++ b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4_compat.c

@@ -114,6 +114,19 @@ static inline void ct_show_secctx(struct seq_file *s, const struct nf_conn *ct)
 }
 #endif
 
+static bool ct_seq_should_skip(const struct nf_conn *ct,
+			       const struct nf_conntrack_tuple_hash *hash)
+{
+	/* we only want to print DIR_ORIGINAL */
+	if (NF_CT_DIRECTION(hash))
+		return true;
+
+	if (nf_ct_l3num(ct) != AF_INET)
+		return true;
+
+	return false;
+}
+
 static int ct_seq_show(struct seq_file *s, void *v)
 {
 	struct nf_conntrack_tuple_hash *hash = v;

@@ -123,14 +136,15 @@ static int ct_seq_show(struct seq_file *s, void *v)
 	int ret = 0;
 
 	NF_CT_ASSERT(ct);
-	if (unlikely(!atomic_inc_not_zero(&ct->ct_general.use)))
+	if (ct_seq_should_skip(ct, hash))
 		return 0;
 
+	if (unlikely(!atomic_inc_not_zero(&ct->ct_general.use)))
+		return 0;
 
-	/* we only want to print DIR_ORIGINAL */
-	if (NF_CT_DIRECTION(hash))
-		goto release;
-	if (nf_ct_l3num(ct) != AF_INET)
+	/* check if we raced w. object reuse */
+	if (!nf_ct_is_confirmed(ct) ||

This refactoring includes this new check, is this intentional?

It seems this check was previously missing, I can just amend the
commit log with a couple of lines to document that this patch also
includes this missing check. No problem.