net: ipv4: fix for a race condition in raw_sendmsg

inet->hdrincl is racy, and could lead to uninitialized stack pointer
usage, so its value should be read only once.

Fixes: c008ba5bdc9f ("ipv4: Avoid reading user iov twice after raw_probe_proto_opt")
Signed-off-by: Mohamed Ghannam <simo.ghannam@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
static int raw_send_hdrinc(struct sock *sk, struct flowi4 *fl4,
			   struct msghdr *msg, size_t length,
			   struct rtable **rtp, unsigned int flags,
			   const struct sockcm_cookie *sockc)
{
	struct inet_sock *inet = inet_sk(sk);
	struct net *net = sock_net(sk);
	struct iphdr *iph;
	struct sk_buff *skb;
	unsigned int iphlen;
	int err;
	struct rtable *rt = *rtp;
	int hlen, tlen;

	if (length > rt->dst.dev->mtu) {
		ip_local_error(sk, EMSGSIZE, fl4->daddr, inet->inet_dport,
			       rt->dst.dev->mtu);
		return -EMSGSIZE;
	}
	if (length < sizeof(struct iphdr))
		return -EINVAL;

	if (flags&MSG_PROBE)
		goto out;

	hlen = LL_RESERVED_SPACE(rt->dst.dev);
	tlen = rt->dst.dev->needed_tailroom;
	skb = sock_alloc_send_skb(sk,
				  length + hlen + tlen + 15,
				  flags & MSG_DONTWAIT, &err);
	if (!skb)
		goto error;
	skb_reserve(skb, hlen);

	skb->priority = sk->sk_priority;
	skb->mark = sk->sk_mark;
	skb_dst_set(skb, &rt->dst);
	*rtp = NULL;

	skb_reset_network_header(skb);
	iph = ip_hdr(skb);
	skb_put(skb, length);

	skb->ip_summed = CHECKSUM_NONE;

	sock_tx_timestamp(sk, sockc->tsflags, &skb_shinfo(skb)->tx_flags);

	if (flags & MSG_CONFIRM)
		skb_set_dst_pending_confirm(skb, 1);

	skb->transport_header = skb->network_header;
	err = -EFAULT;
	if (memcpy_from_msg(iph, msg, length))
		goto error_free;

	iphlen = iph->ihl * 4;

	/*
	 * We don't want to modify the ip header, but we do need to
	 * be sure that it won't cause problems later along the network
	 * stack.  Specifically we want to make sure that iph->ihl is a
	 * sane value.  If ihl points beyond the length of the buffer passed
	 * in, reject the frame as invalid
	 */
	err = -EINVAL;
	if (iphlen > length)
		goto error_free;

	if (iphlen >= sizeof(*iph)) {
		if (!iph->saddr)
			iph->saddr = fl4->saddr;
		iph->check   = 0;
		iph->tot_len = htons(length);
		if (!iph->id)
			ip_select_ident(net, skb, NULL);

		iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
		skb->transport_header += iphlen;
		if (iph->protocol == IPPROTO_ICMP &&
		    length >= iphlen + sizeof(struct icmphdr))
			icmp_out_count(net, ((struct icmphdr *)
				skb_transport_header(skb))->type);
	}

	err = NF_HOOK(NFPROTO_IPV4, NF_INET_LOCAL_OUT,
		      net, sk, skb, NULL, rt->dst.dev,
		      dst_output);
	if (err > 0)
		err = net_xmit_errno(err);
	if (err)
		goto error;
out:
	return 0;

error_free:
	kfree_skb(skb);
error:
	IP_INC_STATS(net, IPSTATS_MIB_OUTDISCARDS);
	if (err == -ENOBUFS && !inet->recverr)
		err = 0;
	return err;
}

static int raw_send_hdrinc(struct sock *sk, struct flowi4 *fl4,
			   struct msghdr *msg, size_t length,
			   struct rtable **rtp, unsigned int flags,
			   const struct sockcm_cookie *sockc)
{
	struct inet_sock *inet = inet_sk(sk);
	struct net *net = sock_net(sk);
	struct iphdr *iph;
	struct sk_buff *skb;
	unsigned int iphlen;
	int err;
	struct rtable *rt = *rtp;
	int hlen, tlen;

	if (length > rt->dst.dev->mtu) {
		ip_local_error(sk, EMSGSIZE, fl4->daddr, inet->inet_dport,
			       rt->dst.dev->mtu);
		return -EMSGSIZE;
	}
	if (length < sizeof(struct iphdr))
		return -EINVAL;

	if (flags&MSG_PROBE)
		goto out;

	hlen = LL_RESERVED_SPACE(rt->dst.dev);
	tlen = rt->dst.dev->needed_tailroom;
	skb = sock_alloc_send_skb(sk,
				  length + hlen + tlen + 15,
				  flags & MSG_DONTWAIT, &err);
	if (!skb)
		goto error;
	skb_reserve(skb, hlen);

	skb->priority = sk->sk_priority;
	skb->mark = sk->sk_mark;
	skb_dst_set(skb, &rt->dst);
	*rtp = NULL;

	skb_reset_network_header(skb);
	iph = ip_hdr(skb);
	skb_put(skb, length);

	skb->ip_summed = CHECKSUM_NONE;

	sock_tx_timestamp(sk, sockc->tsflags, &skb_shinfo(skb)->tx_flags);

	if (flags & MSG_CONFIRM)
		skb_set_dst_pending_confirm(skb, 1);

	skb->transport_header = skb->network_header;
	err = -EFAULT;
	if (memcpy_from_msg(iph, msg, length))
		goto error_free;

	iphlen = iph->ihl * 4;

	/*
	 * We don't want to modify the ip header, but we do need to
	 * be sure that it won't cause problems later along the network
	 * stack.  Specifically we want to make sure that iph->ihl is a
	 * sane value.  If ihl points beyond the length of the buffer passed
	 * in, reject the frame as invalid
	 */
	err = -EINVAL;
	if (iphlen > length)
		goto error_free;

	if (iphlen >= sizeof(*iph)) {
		if (!iph->saddr)
			iph->saddr = fl4->saddr;
		iph->check   = 0;
		iph->tot_len = htons(length);
		if (!iph->id)
			ip_select_ident(net, skb, NULL);

		iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
		skb->transport_header += iphlen;
		if (iph->protocol == IPPROTO_ICMP &&
		    length >= iphlen + sizeof(struct icmphdr))
			icmp_out_count(net, ((struct icmphdr *)
				skb_transport_header(skb))->type);
	}

	err = NF_HOOK(NFPROTO_IPV4, NF_INET_LOCAL_OUT,
		      net, sk, skb, NULL, rt->dst.dev,
		      dst_output);
	if (err > 0)
		err = net_xmit_errno(err);
	if (err)
		goto error;
out:
	return 0;

error_free:
	kfree_skb(skb);
error:
	IP_INC_STATS(net, IPSTATS_MIB_OUTDISCARDS);
	if (err == -ENOBUFS && !inet->recverr)
		err = 0;
	return err;
}
