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 <[e-mail]>
Reported-by: 郭永刚 <[e-mail]>
Signed-off-by: Hannes Frederic Sowa <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/sock.h

···
 				sk_no_check_rx : 1,
 				sk_userlocks : 4,
 				sk_protocol  : 8,
+#define SK_PROTOCOL_MAX U8_MAX
 				sk_type      : 16;
 	kmemcheck_bitfield_end(flags);
 	int			sk_wmem_queued;

net/ax25/af_ax25.c

···
 	struct sock *sk;
 	ax25_cb *ax25;
 
+	if (protocol < 0 || protocol > SK_PROTOCOL_MAX)
+		return -EINVAL;
+
 	if (!net_eq(net, &init_net))
 		return -EAFNOSUPPORT;
 

net/decnet/af_decnet.c

···
 {
 	struct sock *sk;
 
+	if (protocol < 0 || protocol > SK_PROTOCOL_MAX)
+		return -EINVAL;
+
 	if (!net_eq(net, &init_net))
 		return -EAFNOSUPPORT;
 

net/ipv4/af_inet.c

···
 	int try_loading_module = 0;
 	int err;
 
+	if (protocol < 0 || protocol >= IPPROTO_MAX)
+		return -EINVAL;
+
 	sock->state = SS_UNCONNECTED;
 
 	/* Look for the requested type/protocol pair. */

net/ipv6/af_inet6.c

···
 	int try_loading_module = 0;
 	int err;
 
+	if (protocol < 0 || protocol >= IPPROTO_MAX)
+		return -EINVAL;
+
 	/* Look for the requested type/protocol pair. */
 lookup_protocol:
 	err = -ESOCKTNOSUPPORT;

net/irda/af_irda.c

···
 	struct sock *sk;
 	struct irda_sock *self;
 
+	if (protocol < 0 || protocol > SK_PROTOCOL_MAX)
+		return -EINVAL;
+
 	if (net != &init_net)
 		return -EAFNOSUPPORT;