Code:  int cipso_v4_sock_getattr(struct sock *sk, struct netlbl_lsm_secattr *secattr)
 {
	struct ip_options *opt;
 
	opt = inet_sk(sk)->opt;
	if (opt == NULL || opt->cipso == 0)
		return -ENOMSG;
	return cipso_v4_getattr(opt->__data + opt->cipso - sizeof(struct iphdr),
				secattr);
 }

Commit Message: 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>
CWE ID: CWE-362
 int cipso_v4_sock_getattr(struct sock *sk, struct netlbl_lsm_secattr *secattr)
 {
	struct ip_options_rcu *opt;
	int res = -ENOMSG;
 
	rcu_read_lock();
	opt = rcu_dereference(inet_sk(sk)->inet_opt);
	if (opt && opt->opt.cipso)
		res = cipso_v4_getattr(opt->opt.__data +
						opt->opt.cipso -
						sizeof(struct iphdr),
				       secattr);
	rcu_read_unlock();
	return res;
 }
