Code: static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
 			 struct ipcm_cookie *ipc, struct rtable **rtp)
 {
 	struct inet_sock *inet = inet_sk(sk);
	struct ip_options *opt;
 	struct rtable *rt;
 
 	/*
	 * setup for corking.
	 */
	opt = ipc->opt;
	if (opt) {
		if (cork->opt == NULL) {
			cork->opt = kmalloc(sizeof(struct ip_options) + 40,
					    sk->sk_allocation);
 			if (unlikely(cork->opt == NULL))
 				return -ENOBUFS;
 		}
		memcpy(cork->opt, opt, sizeof(struct ip_options) + opt->optlen);
 		cork->flags |= IPCORK_OPT;
 		cork->addr = ipc->addr;
 	}
	rt = *rtp;
	if (unlikely(!rt))
		return -EFAULT;
	/*
	 * We steal reference to this route, caller should not release it
	 */
	*rtp = NULL;
	cork->fragsize = inet->pmtudisc == IP_PMTUDISC_PROBE ?
			 rt->dst.dev->mtu : dst_mtu(rt->dst.path);
	cork->dst = &rt->dst;
	cork->length = 0;
	cork->tx_flags = ipc->tx_flags;
	cork->page = NULL;
	cork->off = 0;

	return 0;
}

Vulnerability Type: DoS 
CWE ID: CWE-362
Summary: Race condition in the IP implementation in the Linux kernel before 3.0 might allow remote attackers to cause a denial of service (slab corruption and system crash) by sending packets to an application that sets socket options during the handling of network traffic.
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>