netfilter: extensions: introduce extension genid count

Multiple netfilter extensions store pointers to external data
in their extension area struct.

Examples:
1. Timeout policies
2. Connection tracking helpers.

No references are taken for these.

When a helper or timeout policy is removed, the conntrack table gets
traversed and affected extensions are cleared.

Conntrack entries not yet in the hashtable are referenced via a special
list, the unconfirmed list.

On removal of a policy or connection tracking helper, the unconfirmed
list gets traversed an all entries are marked as dying, this prevents
them from getting committed to the table at insertion time: core checks
for dying bit, if set, the conntrack entry gets destroyed at confirm
time.

The disadvantage is that each new conntrack has to be added to the percpu
unconfirmed list, and each insertion needs to remove it from this list.
The list is only ever needed when a policy or helper is removed -- a rare
occurrence.

Add a generation ID count: Instead of adding to the list and then
traversing that list on policy/helper removal, increment a counter
that is stored in the extension area.

For unconfirmed conntracks, the extension has the genid valid at ct
allocation time.

Removal of a helper/policy etc. increments the counter.
At confirmation time, validate that ext->genid == global_id.

If the stored number is not the same, do not allow the conntrack
insertion, just like as if a confirmed-list traversal would have flagged
the entry as dying.

After insertion, the genid is no longer relevant (conntrack entries
are now reachable via the conntrack table iterators and is set to 0.

This allows removal of the percpu unconfirmed list.

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

2 files changed, 25 insertions, 16 deletions

diff --git a/include/net/netfilter/nf_conntrack_extend.h b/include/net/netfilter/nf_conntrack_extend.h
index 96635ad2acc7..0b247248b032 100644
--- a/include/net/netfilter/nf_conntrack_extend.h
+++ b/include/net/netfilter/nf_conntrack_extend.h
@@ -34,21 +34,11 @@ enum nf_ct_ext_id {
 	NF_CT_EXT_NUM,
 };
 
-#define NF_CT_EXT_HELPER_TYPE struct nf_conn_help
-#define NF_CT_EXT_NAT_TYPE struct nf_conn_nat
-#define NF_CT_EXT_SEQADJ_TYPE struct nf_conn_seqadj
-#define NF_CT_EXT_ACCT_TYPE struct nf_conn_acct
-#define NF_CT_EXT_ECACHE_TYPE struct nf_conntrack_ecache
-#define NF_CT_EXT_TSTAMP_TYPE struct nf_conn_tstamp
-#define NF_CT_EXT_TIMEOUT_TYPE struct nf_conn_timeout
-#define NF_CT_EXT_LABELS_TYPE struct nf_conn_labels
-#define NF_CT_EXT_SYNPROXY_TYPE struct nf_conn_synproxy
-#define NF_CT_EXT_ACT_CT_TYPE struct nf_conn_act_ct_ext
-
 /* Extensions: optional stuff which isn't permanently in struct. */
 struct nf_ct_ext {
 	u8 offset[NF_CT_EXT_NUM];
 	u8 len;
+	unsigned int gen_id;
 	char data[] __aligned(8);
 };
 
@@ -62,17 +52,28 @@ static inline bool nf_ct_ext_exist(const struct nf_conn *ct, u8 id)
 	return (ct->ext && __nf_ct_ext_exist(ct->ext, id));
 }
 
-static inline void *__nf_ct_ext_find(const struct nf_conn *ct, u8 id)
+void *__nf_ct_ext_find(const struct nf_ct_ext *ext, u8 id);
+
+static inline void *nf_ct_ext_find(const struct nf_conn *ct, u8 id)
 {
-	if (!nf_ct_ext_exist(ct, id))
+	struct nf_ct_ext *ext = ct->ext;
+
+	if (!ext || !__nf_ct_ext_exist(ext, id))
 		return NULL;
 
+	if (unlikely(ext->gen_id))
+		return __nf_ct_ext_find(ext, id);
+
 	return (void *)ct->ext + ct->ext->offset[id];
 }
-#define nf_ct_ext_find(ext, id)	\
-	((id##_TYPE *)__nf_ct_ext_find((ext), (id)))
 
 /* Add this type, returns pointer to data or NULL. */
 void *nf_ct_ext_add(struct nf_conn *ct, enum nf_ct_ext_id id, gfp_t gfp);
 
+/* ext genid.  if ext->id != ext_genid, extensions cannot be used
+ * anymore unless conntrack has CONFIRMED bit set.
+ */
+extern atomic_t nf_conntrack_ext_genid;
+void nf_ct_ext_bump_genid(void);
+
 #endif /* _NF_CONNTRACK_EXTEND_H */
diff --git a/include/net/netfilter/nf_conntrack_labels.h b/include/net/netfilter/nf_conntrack_labels.h
index 3c23298e68ca..66bab6c60d12 100644
--- a/include/net/netfilter/nf_conntrack_labels.h
+++ b/include/net/netfilter/nf_conntrack_labels.h
@@ -17,10 +17,18 @@ struct nf_conn_labels {
 	unsigned long bits[NF_CT_LABELS_MAX_SIZE / sizeof(long)];
 };
 
+/* Can't use nf_ct_ext_find(), flow dissector cannot use symbols
+ * exported by nf_conntrack module.
+ */
 static inline struct nf_conn_labels *nf_ct_labels_find(const struct nf_conn *ct)
 {
 #ifdef CONFIG_NF_CONNTRACK_LABELS
-	return nf_ct_ext_find(ct, NF_CT_EXT_LABELS);
+	struct nf_ct_ext *ext = ct->ext;
+
+	if (!ext || !__nf_ct_ext_exist(ext, NF_CT_EXT_LABELS))
+		return NULL;
+
+	return (void *)ct->ext + ct->ext->offset[NF_CT_EXT_LABELS];
 #else
 	return NULL;
 #endif