net: add validation for the socket syscall protocol argument

郭永刚 reported that one could simply crash the kernel as root by
using a simple program:

	int socket_fd;
	struct sockaddr_in addr;
	addr.sin_port = 0;
	addr.sin_addr.s_addr = INADDR_ANY;
	addr.sin_family = 10;

	socket_fd = socket(10,3,0x40000000);
	connect(socket_fd , &addr,16);

AF_INET, AF_INET6 sockets actually only support 8-bit protocol
identifiers. inet_sock's skc_protocol field thus is sized accordingly,
thus larger protocol identifiers simply cut off the higher bits and
store a zero in the protocol fields.

This could lead to e.g. NULL function pointer because as a result of
the cut off inet_num is zero and we call down to inet_autobind, which
is NULL for raw sockets.

kernel: Call Trace:
kernel:  [<ffffffff816db90e>] ? inet_autobind+0x2e/0x70
kernel:  [<ffffffff816db9a4>] inet_dgram_connect+0x54/0x80
kernel:  [<ffffffff81645069>] SYSC_connect+0xd9/0x110
kernel:  [<ffffffff810ac51b>] ? ptrace_notify+0x5b/0x80
kernel:  [<ffffffff810236d8>] ? syscall_trace_enter_phase2+0x108/0x200
kernel:  [<ffffffff81645e0e>] SyS_connect+0xe/0x10
kernel:  [<ffffffff81779515>] tracesys_phase2+0x84/0x89

I found no particular commit which introduced this problem.

CVE: CVE-2015-8543
Cc: Cong Wang <cwang@twopensource.com>
Reported-by: 郭永刚 <guoyonggang@360.cn>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
static void irda_connect_indication(void *instance, void *sap,
				    struct qos_info *qos, __u32 max_sdu_size,
				    __u8 max_header_size, struct sk_buff *skb)
{
	struct irda_sock *self;
	struct sock *sk;

	self = instance;

	pr_debug("%s(%p)\n", __func__, self);

	sk = instance;
	if (sk == NULL) {
		dev_kfree_skb(skb);
		return;
	}

	/* How much header space do we need to reserve */
	self->max_header_size = max_header_size;

	/* IrTTP max SDU size in transmit direction */
	self->max_sdu_size_tx = max_sdu_size;

	/* Find out what the largest chunk of data that we can transmit is */
	switch (sk->sk_type) {
	case SOCK_STREAM:
		if (max_sdu_size != 0) {
			net_err_ratelimited("%s: max_sdu_size must be 0\n",
					    __func__);
			kfree_skb(skb);
			return;
		}
		self->max_data_size = irttp_get_max_seg_size(self->tsap);
		break;
	case SOCK_SEQPACKET:
		if (max_sdu_size == 0) {
			net_err_ratelimited("%s: max_sdu_size cannot be 0\n",
					    __func__);
			kfree_skb(skb);
			return;
		}
		self->max_data_size = max_sdu_size;
		break;
	default:
		self->max_data_size = irttp_get_max_seg_size(self->tsap);
	}

	pr_debug("%s(), max_data_size=%d\n", __func__,
		 self->max_data_size);

	memcpy(&self->qos_tx, qos, sizeof(struct qos_info));

	skb_queue_tail(&sk->sk_receive_queue, skb);
	sk->sk_state_change(sk);
}

static void irda_connect_indication(void *instance, void *sap,
				    struct qos_info *qos, __u32 max_sdu_size,
				    __u8 max_header_size, struct sk_buff *skb)
{
	struct irda_sock *self;
	struct sock *sk;

	self = instance;

	pr_debug("%s(%p)\n", __func__, self);

	sk = instance;
	if (sk == NULL) {
		dev_kfree_skb(skb);
		return;
	}

	/* How much header space do we need to reserve */
	self->max_header_size = max_header_size;

	/* IrTTP max SDU size in transmit direction */
	self->max_sdu_size_tx = max_sdu_size;

	/* Find out what the largest chunk of data that we can transmit is */
	switch (sk->sk_type) {
	case SOCK_STREAM:
		if (max_sdu_size != 0) {
			net_err_ratelimited("%s: max_sdu_size must be 0\n",
					    __func__);
			kfree_skb(skb);
			return;
		}
		self->max_data_size = irttp_get_max_seg_size(self->tsap);
		break;
	case SOCK_SEQPACKET:
		if (max_sdu_size == 0) {
			net_err_ratelimited("%s: max_sdu_size cannot be 0\n",
					    __func__);
			kfree_skb(skb);
			return;
		}
		self->max_data_size = max_sdu_size;
		break;
	default:
		self->max_data_size = irttp_get_max_seg_size(self->tsap);
	}

	pr_debug("%s(), max_data_size=%d\n", __func__,
		 self->max_data_size);

	memcpy(&self->qos_tx, qos, sizeof(struct qos_info));

	skb_queue_tail(&sk->sk_receive_queue, skb);
	sk->sk_state_change(sk);
}
