netfilter: conntrack: move code to linux/nf_conntrack_common.h.

Move some `struct nf_conntrack` code from linux/skbuff.h to
linux/nf_conntrack_common.h. Together with a couple of helpers for
getting and setting skb->_nfct, it allows us to remove
CONFIG_NF_CONNTRACK checks from net/netfilter/nf_conntrack.h.

Signed-off-by: Jeremy Sowden <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/linux/netfilter/nf_conntrack_common.h

···
 #ifndef _NF_CONNTRACK_COMMON_H
 #define _NF_CONNTRACK_COMMON_H
 
+#include <linux/atomic.h>
 #include <uapi/linux/netfilter/nf_conntrack_common.h>
 
 struct ip_conntrack_stat {
···
 	unsigned int expect_delete;
 	unsigned int search_restart;
 };
+
+#define NFCT_INFOMASK	7UL
+#define NFCT_PTRMASK	~(NFCT_INFOMASK)
+
+struct nf_conntrack {
+	atomic_t use;
+};
+
+void nf_conntrack_destroy(struct nf_conntrack *nfct);
+static inline void nf_conntrack_put(struct nf_conntrack *nfct)
+{
+	if (nfct && atomic_dec_and_test(&nfct->use))
+		nf_conntrack_destroy(nfct);
+}
+static inline void nf_conntrack_get(struct nf_conntrack *nfct)
+{
+	if (nfct)
+		atomic_inc(&nfct->use);
+}
 
 #endif /* _NF_CONNTRACK_COMMON_H */

include/linux/skbuff.h

···
 #include <linux/in6.h>
 #include <linux/if_packet.h>
 #include <net/flow.h>
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+#include <linux/netfilter/nf_conntrack_common.h>
+#endif
 
 /* The interface for checksum offload between the stack and networking drivers
  * is as follows...
···
 struct bpf_prog;
 union bpf_attr;
 struct skb_ext;
-
-#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
-struct nf_conntrack {
-	atomic_t use;
-};
-#endif
 
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 struct nf_bridge_info {
···
 #define SKB_DST_NOREF	1UL
 #define SKB_DST_PTRMASK	~(SKB_DST_NOREF)
 
-#define SKB_NFCT_PTRMASK	~(7UL)
 /**
  * skb_dst - returns skb dst_entry
  * @skb: buffer
···
 static inline struct nf_conntrack *skb_nfct(const struct sk_buff *skb)
 {
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
-	return (void *)(skb->_nfct & SKB_NFCT_PTRMASK);
+	return (void *)(skb->_nfct & NFCT_PTRMASK);
 #else
 	return NULL;
 #endif
 }
 
-#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
-void nf_conntrack_destroy(struct nf_conntrack *nfct);
-static inline void nf_conntrack_put(struct nf_conntrack *nfct)
+static inline unsigned long skb_get_nfct(const struct sk_buff *skb)
 {
-	if (nfct && atomic_dec_and_test(&nfct->use))
-		nf_conntrack_destroy(nfct);
-}
-static inline void nf_conntrack_get(struct nf_conntrack *nfct)
-{
-	if (nfct)
-		atomic_inc(&nfct->use);
-}
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+	return skb->_nfct;
+#else
+	return 0UL;
 #endif
+}
+
+static inline void skb_set_nfct(struct sk_buff *skb, unsigned long nfct)
+{
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+	skb->_nfct = nfct;
+#endif
+}
 
 #ifdef CONFIG_SKB_EXTENSIONS
 enum skb_ext_id {

include/net/netfilter/nf_conntrack.h

···
 #ifndef _NF_CONNTRACK_H
 #define _NF_CONNTRACK_H
 
-#include <linux/netfilter/nf_conntrack_common.h>
-
 #include <linux/bitops.h>
 #include <linux/compiler.h>
-#include <linux/atomic.h>
 
+#include <linux/netfilter/nf_conntrack_common.h>
 #include <linux/netfilter/nf_conntrack_tcp.h>
 #include <linux/netfilter/nf_conntrack_dccp.h>
 #include <linux/netfilter/nf_conntrack_sctp.h>
···
 #include <net/netfilter/ipv6/nf_conntrack_ipv6.h>
 
 struct nf_conn {
-#if IS_ENABLED(CONFIG_NF_CONNTRACK)
 	/* Usage count in here is 1 for hash table, 1 per skb,
 	 * plus 1 for any connection(s) we are `master' for
 	 *
···
 	 * beware nf_ct_get() is different and don't inc refcnt.
 	 */
 	struct nf_conntrack ct_general;
-#endif
 
 	spinlock_t	lock;
 	/* jiffies32 when this ct is considered dead */
···
 int nf_conntrack_tuple_taken(const struct nf_conntrack_tuple *tuple,
 			     const struct nf_conn *ignored_conntrack);
 
-#if IS_ENABLED(CONFIG_NF_CONNTRACK)
-
-#define NFCT_INFOMASK	7UL
-#define NFCT_PTRMASK	~(NFCT_INFOMASK)
-
 /* Return conntrack_info and tuple hash for given skb. */
 static inline struct nf_conn *
 nf_ct_get(const struct sk_buff *skb, enum ip_conntrack_info *ctinfo)
 {
-	*ctinfo = skb->_nfct & NFCT_INFOMASK;
+	unsigned long nfct = skb_get_nfct(skb);
 
-	return (struct nf_conn *)(skb->_nfct & NFCT_PTRMASK);
+	*ctinfo = nfct & NFCT_INFOMASK;
+	return (struct nf_conn *)(nfct & NFCT_PTRMASK);
 }
 
 /* decrement reference count on a conntrack */
···
 	WARN_ON(!ct);
 	nf_conntrack_put(&ct->ct_general);
 }
-
-#endif
 
 /* Protocol module loading */
 int nf_ct_l3proto_try_module_get(unsigned short l3proto);
···
 
 u32 nf_ct_get_id(const struct nf_conn *ct);
 
-#if IS_ENABLED(CONFIG_NF_CONNTRACK)
-
 static inline void
 nf_ct_set(struct sk_buff *skb, struct nf_conn *ct, enum ip_conntrack_info info)
 {
-	skb->_nfct = (unsigned long)ct | info;
+	skb_set_nfct(skb, (unsigned long)ct | info);
 }
-
-#endif
 
 #define NF_CT_STAT_INC(net, count)	  __this_cpu_inc((net)->ct.stat->count)
 #define NF_CT_STAT_INC_ATOMIC(net, count) this_cpu_inc((net)->ct.stat->count)

net/netfilter/nf_conntrack_standalone.c

···
 	if (ret < 0)
 		goto out_start;
 
-	BUILD_BUG_ON(SKB_NFCT_PTRMASK != NFCT_PTRMASK);
 	BUILD_BUG_ON(NFCT_INFOMASK <= IP_CT_NUMBER);
 
 #ifdef CONFIG_SYSCTL