net/packet: fix overflow in check for tp_reserve

When calculating po->tp_hdrlen + po->tp_reserve the result can overflow.

Fix by checking that tp_reserve <= INT_MAX on assign.
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

BugLink: https://bugs.launchpad.net/bugs/1678009
CVE-2017-7308
(cherry picked from commit bcc5364b linux-net)
Signed-off-by: Andy Whitcroft <apw@canonical.com>

net/packet/af_packet.c

@@ -3602,6 +3602,8 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
 			return -EBUSY;
 		if (copy_from_user(&val, optval, sizeof(val)))
 			return -EFAULT;
+		if (val > INT_MAX)
+			return -EINVAL;
 		po->tp_reserve = val;
 		return 0;
 	}