inet: add RCU protection to inet->opt

We lack proper synchronization to manipulate inet->opt ip_options

Problem is ip_make_skb() calls ip_setup_cork() and
ip_setup_cork() possibly makes a copy of ipc->opt (struct ip_options),
without any protection against another thread manipulating inet->opt.

Another thread can change inet->opt pointer and free old one under us.

Use RCU to protect inet->opt (changed to inet->inet_opt).

Instead of handling atomic refcounts, just copy ip_options when
necessary, to avoid cache line dirtying.

We cant insert an rcu_head in struct ip_options since its included in
skb->cb[], so this patch is large because I had to introduce a new
ip_options_rcu structure.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
int cipso_v4_cache_add(const struct sk_buff *skb,
		       const struct netlbl_lsm_secattr *secattr)
{
	int ret_val = -EPERM;
	u32 bkt;
	struct cipso_v4_map_cache_entry *entry = NULL;
	struct cipso_v4_map_cache_entry *old_entry = NULL;
	unsigned char *cipso_ptr;
	u32 cipso_ptr_len;

	if (!cipso_v4_cache_enabled || cipso_v4_cache_bucketsize <= 0)
		return 0;

	cipso_ptr = CIPSO_V4_OPTPTR(skb);
	cipso_ptr_len = cipso_ptr[1];

	entry = kzalloc(sizeof(*entry), GFP_ATOMIC);
	if (entry == NULL)
		return -ENOMEM;
	entry->key = kmemdup(cipso_ptr, cipso_ptr_len, GFP_ATOMIC);
	if (entry->key == NULL) {
		ret_val = -ENOMEM;
		goto cache_add_failure;
	}
	entry->key_len = cipso_ptr_len;
	entry->hash = cipso_v4_map_cache_hash(cipso_ptr, cipso_ptr_len);
	atomic_inc(&secattr->cache->refcount);
	entry->lsm_data = secattr->cache;

	bkt = entry->hash & (CIPSO_V4_CACHE_BUCKETS - 1);
	spin_lock_bh(&cipso_v4_cache[bkt].lock);
	if (cipso_v4_cache[bkt].size < cipso_v4_cache_bucketsize) {
		list_add(&entry->list, &cipso_v4_cache[bkt].list);
		cipso_v4_cache[bkt].size += 1;
	} else {
		old_entry = list_entry(cipso_v4_cache[bkt].list.prev,
				       struct cipso_v4_map_cache_entry, list);
		list_del(&old_entry->list);
		list_add(&entry->list, &cipso_v4_cache[bkt].list);
		cipso_v4_cache_entry_free(old_entry);
	}
	spin_unlock_bh(&cipso_v4_cache[bkt].lock);

	return 0;

cache_add_failure:
	if (entry)
		cipso_v4_cache_entry_free(entry);
	return ret_val;
}

int cipso_v4_cache_add(const struct sk_buff *skb,
		       const struct netlbl_lsm_secattr *secattr)
{
	int ret_val = -EPERM;
	u32 bkt;
	struct cipso_v4_map_cache_entry *entry = NULL;
	struct cipso_v4_map_cache_entry *old_entry = NULL;
	unsigned char *cipso_ptr;
	u32 cipso_ptr_len;

	if (!cipso_v4_cache_enabled || cipso_v4_cache_bucketsize <= 0)
		return 0;

	cipso_ptr = CIPSO_V4_OPTPTR(skb);
	cipso_ptr_len = cipso_ptr[1];

	entry = kzalloc(sizeof(*entry), GFP_ATOMIC);
	if (entry == NULL)
		return -ENOMEM;
	entry->key = kmemdup(cipso_ptr, cipso_ptr_len, GFP_ATOMIC);
	if (entry->key == NULL) {
		ret_val = -ENOMEM;
		goto cache_add_failure;
	}
	entry->key_len = cipso_ptr_len;
	entry->hash = cipso_v4_map_cache_hash(cipso_ptr, cipso_ptr_len);
	atomic_inc(&secattr->cache->refcount);
	entry->lsm_data = secattr->cache;

	bkt = entry->hash & (CIPSO_V4_CACHE_BUCKETS - 1);
	spin_lock_bh(&cipso_v4_cache[bkt].lock);
	if (cipso_v4_cache[bkt].size < cipso_v4_cache_bucketsize) {
		list_add(&entry->list, &cipso_v4_cache[bkt].list);
		cipso_v4_cache[bkt].size += 1;
	} else {
		old_entry = list_entry(cipso_v4_cache[bkt].list.prev,
				       struct cipso_v4_map_cache_entry, list);
		list_del(&old_entry->list);
		list_add(&entry->list, &cipso_v4_cache[bkt].list);
		cipso_v4_cache_entry_free(old_entry);
	}
	spin_unlock_bh(&cipso_v4_cache[bkt].lock);

	return 0;

cache_add_failure:
	if (entry)
		cipso_v4_cache_entry_free(entry);
	return ret_val;
}
