netfilter: conntrack: free extension area immediately

Instead of waiting for rcu grace period just free it directly.

This is safe because conntrack lookup doesn't consider extensions.

Other accesses happen while ct->ext can't be free'd, either because
a ct refcount was taken or because the conntrack hash bucket lock or
the dying list spinlock have been taken.

This allows to remove __krealloc in a followup patch, netfilter was the
only user.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_conntrack_extend.h

@@ -43,7 +43,6 @@ enum nf_ct_ext_id {
 
 /* Extensions: optional stuff which isn't permanently in struct. */
 struct nf_ct_ext {
-	struct rcu_head rcu;
 	u8 offset[NF_CT_EXT_NUM];
 	u8 len;
 	char data[0];
@@ -72,15 +71,6 @@ static inline void *__nf_ct_ext_find(const struct nf_conn *ct, u8 id)
 /* Destroy all relationships */
 void nf_ct_ext_destroy(struct nf_conn *ct);
 
-/* Free operation. If you want to free a object referred from private area,
- * please implement __nf_ct_ext_free() and call it.
- */
-static inline void nf_ct_ext_free(struct nf_conn *ct)
-{
-	if (ct->ext)
-		kfree_rcu(ct->ext, rcu);
-}
-
 /* 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);
 

net/netfilter/nf_conntrack_core.c

@@ -573,7 +573,6 @@ EXPORT_SYMBOL_GPL(nf_ct_tmpl_alloc);
 void nf_ct_tmpl_free(struct nf_conn *tmpl)
 {
 	nf_ct_ext_destroy(tmpl);
-	nf_ct_ext_free(tmpl);
 
 	if (ARCH_KMALLOC_MINALIGN <= NFCT_INFOMASK)
 		kfree((char *)tmpl - tmpl->proto.tmpl_padto);
@@ -1417,7 +1416,6 @@ void nf_conntrack_free(struct nf_conn *ct)
 	WARN_ON(atomic_read(&ct->ct_general.use) != 0);
 
 	nf_ct_ext_destroy(ct);
-	nf_ct_ext_free(ct);
 	kmem_cache_free(nf_conntrack_cachep, ct);
 	smp_mb__before_atomic();
 	atomic_dec(&net->ct.count);

net/netfilter/nf_conntrack_extend.c

@@ -34,21 +34,24 @@ void nf_ct_ext_destroy(struct nf_conn *ct)
 			t->destroy(ct);
 		rcu_read_unlock();
 	}
+
+	kfree(ct->ext);
 }
 EXPORT_SYMBOL(nf_ct_ext_destroy);
 
 void *nf_ct_ext_add(struct nf_conn *ct, enum nf_ct_ext_id id, gfp_t gfp)
 {
 	unsigned int newlen, newoff, oldlen, alloc;
-	struct nf_ct_ext *old, *new;
 	struct nf_ct_ext_type *t;
+	struct nf_ct_ext *new;
 
 	/* Conntrack must not be confirmed to avoid races on reallocation. */
 	WARN_ON(nf_ct_is_confirmed(ct));
 
-	old = ct->ext;
 
-	if (old) {
+	if (ct->ext) {
+		const struct nf_ct_ext *old = ct->ext;
+
 		if (__nf_ct_ext_exist(old, id))
 			return NULL;
 		oldlen = old->len;
@@ -68,22 +71,18 @@ void *nf_ct_ext_add(struct nf_conn *ct, enum nf_ct_ext_id id, gfp_t gfp)
 	rcu_read_unlock();
 
 	alloc = max(newlen, NF_CT_EXT_PREALLOC);
-	kmemleak_not_leak(old);
-	new = __krealloc(old, alloc, gfp);
+	new = krealloc(ct->ext, alloc, gfp);
 	if (!new)
 		return NULL;
 
-	if (!old) {
+	if (!ct->ext)
 		memset(new->offset, 0, sizeof(new->offset));
-		ct->ext = new;
-	} else if (new != old) {
-		kfree_rcu(old, rcu);
-		rcu_assign_pointer(ct->ext, new);
-	}
 
 	new->offset[id] = newoff;
 	new->len = newlen;
 	memset((void *)new + newoff, 0, newlen - newoff);
+
+	ct->ext = new;
 	return (void *)new + newoff;
 }
 EXPORT_SYMBOL(nf_ct_ext_add);