[NETFILTER]: nf_conntrack: replace horrible hack with ksize()

There's a horrible slab abuse in net/netfilter/nf_conntrack_extend.c
that can be replaced with a call to ksize().

Cc: Christoph Lameter <[e-mail]>
Signed-off-by: Pekka Enberg <[e-mail]>
Signed-off-by: Patrick McHardy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/netfilter/nf_conntrack_extend.h

···
 struct nf_ct_ext {
 	u8 offset[NF_CT_EXT_NUM];
 	u8 len;
-	u8 real_len;
 	char data[0];
 };
 

net/netfilter/nf_conntrack_extend.c

···
 static struct nf_ct_ext_type *nf_ct_ext_types[NF_CT_EXT_NUM];
 static DEFINE_MUTEX(nf_ct_ext_type_mutex);
 
-/* Horrible trick to figure out smallest amount worth kmallocing. */
-#define CACHE(x) (x) + 0 *
-enum {
-	NF_CT_EXT_MIN_SIZE =
-#include <linux/kmalloc_sizes.h>
-	1 };
-#undef CACHE
-
 void __nf_ct_ext_destroy(struct nf_conn *ct)
 {
 	unsigned int i;
···
 static void *
 nf_ct_ext_create(struct nf_ct_ext **ext, enum nf_ct_ext_id id, gfp_t gfp)
 {
-	unsigned int off, len, real_len;
+	unsigned int off, len;
 	struct nf_ct_ext_type *t;
 
 	rcu_read_lock();
···
 	BUG_ON(t == NULL);
 	off = ALIGN(sizeof(struct nf_ct_ext), t->align);
 	len = off + t->len;
-	real_len = t->alloc_size;
 	rcu_read_unlock();
 
-	*ext = kzalloc(real_len, gfp);
+	*ext = kzalloc(t->alloc_size, gfp);
 	if (!*ext)
 		return NULL;
 
 	(*ext)->offset[id] = off;
 	(*ext)->len = len;
-	(*ext)->real_len = real_len;
 
 	return (void *)(*ext) + off;
 }
···
 	newlen = newoff + t->len;
 	rcu_read_unlock();
 
-	if (newlen >= ct->ext->real_len) {
+	if (newlen >= ksize(ct->ext)) {
 		new = kmalloc(newlen, gfp);
 		if (!new)
 			return NULL;
···
 			rcu_read_unlock();
 		}
 		kfree(ct->ext);
-		new->real_len = newlen;
 		ct->ext = new;
 	}
 
···
 			t1->alloc_size = ALIGN(t1->alloc_size, t2->align)
 					 + t2->len;
 		}
-		if (t1->alloc_size < NF_CT_EXT_MIN_SIZE)
-			t1->alloc_size = NF_CT_EXT_MIN_SIZE;
 	}
 }