Code: static int vmci_transport_dgram_dequeue(struct kiocb *kiocb,
					struct vsock_sock *vsk,
					struct msghdr *msg, size_t len,
					int flags)
{
	int err;
	int noblock;
	struct vmci_datagram *dg;
	size_t payload_len;
	struct sk_buff *skb;

	noblock = flags & MSG_DONTWAIT;

 	if (flags & MSG_OOB || flags & MSG_ERRQUEUE)
 		return -EOPNOTSUPP;
 
 	/* Retrieve the head sk_buff from the socket's receive queue. */
 	err = 0;
 	skb = skb_recv_datagram(&vsk->sk, flags, noblock, &err);
	if (err)
		return err;

	if (!skb)
		return -EAGAIN;

	dg = (struct vmci_datagram *)skb->data;
	if (!dg)
		/* err is 0, meaning we read zero bytes. */
		goto out;

	payload_len = dg->payload_size;
	/* Ensure the sk_buff matches the payload size claimed in the packet. */
	if (payload_len != skb->len - sizeof(*dg)) {
		err = -EINVAL;
		goto out;
	}

	if (payload_len > len) {
		payload_len = len;
		msg->msg_flags |= MSG_TRUNC;
	}

	/* Place the datagram payload in the user's iovec. */
	err = skb_copy_datagram_iovec(skb, sizeof(*dg), msg->msg_iov,
		payload_len);
 	if (err)
 		goto out;
 
	msg->msg_namelen = 0;
 	if (msg->msg_name) {
 		struct sockaddr_vm *vm_addr;
 
		/* Provide the address of the sender. */
		vm_addr = (struct sockaddr_vm *)msg->msg_name;
		vsock_addr_init(vm_addr, dg->src.context, dg->src.resource);
		msg->msg_namelen = sizeof(*vm_addr);
	}
	err = payload_len;

out:
	skb_free_datagram(&vsk->sk, skb);
	return err;
}

Vulnerability Type: +Info 
CWE ID: CWE-200
Summary: The vmci_transport_dgram_dequeue function in net/vmw_vsock/vmci_transport.c in the Linux kernel before 3.9-rc7 does not properly initialize a certain length variable, which allows local users to obtain sensitive information from kernel stack memory via a crafted recvmsg or recvfrom system call.
Commit Message: VSOCK: vmci - fix possible info leak in vmci_transport_dgram_dequeue()

In case we received no data on the call to skb_recv_datagram(), i.e.
skb->data is NULL, vmci_transport_dgram_dequeue() will return with 0
without updating msg_namelen leading to net/socket.c leaking the local,
uninitialized sockaddr_storage variable to userland -- 128 bytes of
kernel stack memory.

Fix this by moving the already existing msg_namelen assignment a few
lines above.

Cc: Andy King <acking@vmware.com>
Cc: Dmitry Torokhov <dtor@vmware.com>
Cc: George Zhang <georgezhang@vmware.com>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>