wireless: wext: terminate ifr name coming from userspace

ifr name is assumed to be a valid string by the kernel, but nothing
was forcing username to pass a valid string.

In turn, this would cause panics as we tried to access the string
past it's valid memory.
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev_ioctl.c

@@ -424,6 +424,8 @@ int dev_ioctl(struct net *net, unsigned int cmd, void __user *arg)
 		if (copy_from_user(&iwr, arg, sizeof(iwr)))
 			return -EFAULT;
 
+		iwr.ifr_name[sizeof(iwr.ifr_name) - 1] = 0;
+
 		return wext_handle_ioctl(net, &iwr, cmd, arg);
 	}