Code: int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
		size_t len)
{
	struct inet_sock *inet = inet_sk(sk);
	struct udp_sock *up = udp_sk(sk);
	struct flowi4 *fl4;
	int ulen = len;
	struct ipcm_cookie ipc;
	struct rtable *rt = NULL;
	int free = 0;
	int connected = 0;
	__be32 daddr, faddr, saddr;
	__be16 dport;
	u8  tos;
	int err, is_udplite = IS_UDPLITE(sk);
 	int corkreq = up->corkflag || msg->msg_flags&MSG_MORE;
 	int (*getfrag)(void *, char *, int, int, int, struct sk_buff *);
 	struct sk_buff *skb;
 
 	if (len > 0xFFFF)
 		return -EMSGSIZE;

	/*
	 *	Check the flags.
	 */

	if (msg->msg_flags & MSG_OOB) /* Mirror BSD error message compatibility */
		return -EOPNOTSUPP;

	ipc.opt = NULL;
	ipc.tx_flags = 0;

	getfrag = is_udplite ? udplite_getfrag : ip_generic_getfrag;

	if (up->pending) {
		/*
		 * There are pending frames.
		 * The socket lock must be held while it's corked.
		 */
		lock_sock(sk);
		if (likely(up->pending)) {
			if (unlikely(up->pending != AF_INET)) {
				release_sock(sk);
				return -EINVAL;
			}
			goto do_append_data;
		}
		release_sock(sk);
	}
	ulen += sizeof(struct udphdr);

	/*
	 *	Get and verify the address.
	 */
	if (msg->msg_name) {
		struct sockaddr_in * usin = (struct sockaddr_in *)msg->msg_name;
		if (msg->msg_namelen < sizeof(*usin))
			return -EINVAL;
		if (usin->sin_family != AF_INET) {
			if (usin->sin_family != AF_UNSPEC)
				return -EAFNOSUPPORT;
		}

		daddr = usin->sin_addr.s_addr;
		dport = usin->sin_port;
		if (dport == 0)
			return -EINVAL;
	} else {
		if (sk->sk_state != TCP_ESTABLISHED)
			return -EDESTADDRREQ;
		daddr = inet->inet_daddr;
		dport = inet->inet_dport;
		/* Open fast path for connected socket.
		   Route will not be used, if at least one option is set.
		 */
		connected = 1;
	}
	ipc.addr = inet->inet_saddr;

	ipc.oif = sk->sk_bound_dev_if;
	err = sock_tx_timestamp(sk, &ipc.tx_flags);
	if (err)
		return err;
	if (msg->msg_controllen) {
		err = ip_cmsg_send(sock_net(sk), msg, &ipc);
		if (err)
			return err;
		if (ipc.opt)
 			free = 1;
 		connected = 0;
 	}
	if (!ipc.opt)
		ipc.opt = inet->opt;
 
 	saddr = ipc.addr;
 	ipc.addr = faddr = daddr;
 
	if (ipc.opt && ipc.opt->srr) {
 		if (!daddr)
 			return -EINVAL;
		faddr = ipc.opt->faddr;
 		connected = 0;
 	}
 	tos = RT_TOS(inet->tos);
 	if (sock_flag(sk, SOCK_LOCALROUTE) ||
 	    (msg->msg_flags & MSG_DONTROUTE) ||
	    (ipc.opt && ipc.opt->is_strictroute)) {
 		tos |= RTO_ONLINK;
 		connected = 0;
 	}

	if (ipv4_is_multicast(daddr)) {
		if (!ipc.oif)
			ipc.oif = inet->mc_index;
		if (!saddr)
			saddr = inet->mc_addr;
		connected = 0;
	}

	if (connected)
		rt = (struct rtable *)sk_dst_check(sk, 0);

	if (rt == NULL) {
		struct flowi4 fl4;
		struct net *net = sock_net(sk);

		flowi4_init_output(&fl4, ipc.oif, sk->sk_mark, tos,
				   RT_SCOPE_UNIVERSE, sk->sk_protocol,
				   inet_sk_flowi_flags(sk)|FLOWI_FLAG_CAN_SLEEP,
				   faddr, saddr, dport, inet->inet_sport);

		security_sk_classify_flow(sk, flowi4_to_flowi(&fl4));
		rt = ip_route_output_flow(net, &fl4, sk);
		if (IS_ERR(rt)) {
			err = PTR_ERR(rt);
			rt = NULL;
			if (err == -ENETUNREACH)
				IP_INC_STATS_BH(net, IPSTATS_MIB_OUTNOROUTES);
			goto out;
		}

		err = -EACCES;
		if ((rt->rt_flags & RTCF_BROADCAST) &&
		    !sock_flag(sk, SOCK_BROADCAST))
			goto out;
		if (connected)
			sk_dst_set(sk, dst_clone(&rt->dst));
	}

	if (msg->msg_flags&MSG_CONFIRM)
		goto do_confirm;
back_from_confirm:

	saddr = rt->rt_src;
	if (!ipc.addr)
		daddr = ipc.addr = rt->rt_dst;

	/* Lockless fast path for the non-corking case. */
	if (!corkreq) {
		skb = ip_make_skb(sk, getfrag, msg->msg_iov, ulen,
				  sizeof(struct udphdr), &ipc, &rt,
				  msg->msg_flags);
		err = PTR_ERR(skb);
		if (skb && !IS_ERR(skb))
			err = udp_send_skb(skb, daddr, dport);
		goto out;
	}

	lock_sock(sk);
	if (unlikely(up->pending)) {
		/* The socket is already corked while preparing it. */
		/* ... which is an evident application bug. --ANK */
		release_sock(sk);

		LIMIT_NETDEBUG(KERN_DEBUG "udp cork app bug 2\n");
		err = -EINVAL;
		goto out;
	}
	/*
	 *	Now cork the socket to pend data.
	 */
	fl4 = &inet->cork.fl.u.ip4;
	fl4->daddr = daddr;
	fl4->saddr = saddr;
	fl4->fl4_dport = dport;
	fl4->fl4_sport = inet->inet_sport;
	up->pending = AF_INET;

do_append_data:
	up->len += ulen;
	err = ip_append_data(sk, getfrag, msg->msg_iov, ulen,
			sizeof(struct udphdr), &ipc, &rt,
			corkreq ? msg->msg_flags|MSG_MORE : msg->msg_flags);
	if (err)
		udp_flush_pending_frames(sk);
	else if (!corkreq)
		err = udp_push_pending_frames(sk);
	else if (unlikely(skb_queue_empty(&sk->sk_write_queue)))
		up->pending = 0;
	release_sock(sk);

out:
	ip_rt_put(rt);
	if (free)
		kfree(ipc.opt);
	if (!err)
		return len;
	/*
	 * ENOBUFS = no kernel mem, SOCK_NOSPACE = no sndbuf space.  Reporting
	 * ENOBUFS might not be good (it's not tunable per se), but otherwise
	 * we don't have a good statistic (IpOutDiscards but it can be too many
	 * things).  We could add another new stat but at least for now that
	 * seems like overkill.
	 */
	if (err == -ENOBUFS || test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
		UDP_INC_STATS_USER(sock_net(sk),
				UDP_MIB_SNDBUFERRORS, is_udplite);
	}
	return err;

do_confirm:
	dst_confirm(&rt->dst);
	if (!(msg->msg_flags&MSG_PROBE) || len)
		goto back_from_confirm;
	err = 0;
	goto out;
}

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>