netfilter: conntrack: support a fixed size of 128 distinct labels

The conntrack label extension is currently variable-sized, e.g. if
only 2 labels are used by iptables rules then the labels->bits[] array
will only contain one element.

We track size of each label storage area in the 'words' member.

But in nftables and openvswitch we always have to ask for worst-case
since we don't know what bit will be used at configuration time.

As most arches are 64bit we need to allocate 24 bytes in this case:

struct nf_conn_labels {
    u8            words;   /*     0     1 */
    /* XXX 7 bytes hole, try to pack */
    long unsigned bits[2]; /*     8     24 */

Make bits a fixed size and drop the words member, it simplifies
the code and only increases memory requirements on x86 when
less than 64bit labels are required.

We still only allocate the extension if its needed.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 4 insertions, 12 deletions

diff --git a/include/net/netfilter/nf_conntrack_labels.h b/include/net/netfilter/nf_conntrack_labels.h
index c5f8fc736b3d..0fd4989de836 100644
--- a/include/net/netfilter/nf_conntrack_labels.h
+++ b/include/net/netfilter/nf_conntrack_labels.h
@@ -10,8 +10,7 @@
 #define NF_CT_LABELS_MAX_SIZE ((XT_CONNLABEL_MAXBIT + 1) / BITS_PER_BYTE)
 
 struct nf_conn_labels {
-	u8 words;
-	unsigned long bits[];
+	unsigned long bits[NF_CT_LABELS_MAX_SIZE / sizeof(long)];
 };
 
 static inline struct nf_conn_labels *nf_ct_labels_find(const struct nf_conn *ct)
@@ -26,20 +25,13 @@ static inline struct nf_conn_labels *nf_ct_labels_find(const struct nf_conn *ct)
 static inline struct nf_conn_labels *nf_ct_labels_ext_add(struct nf_conn *ct)
 {
 #ifdef CONFIG_NF_CONNTRACK_LABELS
-	struct nf_conn_labels *cl_ext;
 	struct net *net = nf_ct_net(ct);
-	u8 words;
 
-	words = ACCESS_ONCE(net->ct.label_words);
-	if (words == 0)
+	if (net->ct.labels_used == 0)
 		return NULL;
 
-	cl_ext = nf_ct_ext_add_length(ct, NF_CT_EXT_LABELS,
-				      words * sizeof(long), GFP_ATOMIC);
-	if (cl_ext != NULL)
-		cl_ext->words = words;
-
-	return cl_ext;
+	return nf_ct_ext_add_length(ct, NF_CT_EXT_LABELS,
+				    sizeof(struct nf_conn_labels), GFP_ATOMIC);
 #else
 	return NULL;
 #endif