Code: static int llcp_sock_recvmsg(struct kiocb *iocb, struct socket *sock,
			     struct msghdr *msg, size_t len, int flags)
{
	int noblock = flags & MSG_DONTWAIT;
	struct sock *sk = sock->sk;
	unsigned int copied, rlen;
	struct sk_buff *skb, *cskb;
	int err = 0;
 
 	pr_debug("%p %zu\n", sk, len);
 
 	lock_sock(sk);
 
 	if (sk->sk_state == LLCP_CLOSED &&
	    skb_queue_empty(&sk->sk_receive_queue)) {
		release_sock(sk);
		return 0;
	}

	release_sock(sk);

	if (flags & (MSG_OOB))
		return -EOPNOTSUPP;

	skb = skb_recv_datagram(sk, flags, noblock, &err);
	if (!skb) {
		pr_err("Recv datagram failed state %d %d %d",
		       sk->sk_state, err, sock_error(sk));

		if (sk->sk_shutdown & RCV_SHUTDOWN)
			return 0;

		return err;
	}

	rlen = skb->len;		/* real length of skb */
	copied = min_t(unsigned int, rlen, len);

	cskb = skb;
	if (skb_copy_datagram_iovec(cskb, 0, msg->msg_iov, copied)) {
		if (!(flags & MSG_PEEK))
			skb_queue_head(&sk->sk_receive_queue, skb);
		return -EFAULT;
	}

	sock_recv_timestamp(msg, sk, skb);

	if (sk->sk_type == SOCK_DGRAM && msg->msg_name) {
		struct nfc_llcp_ui_cb *ui_cb = nfc_llcp_ui_skb_cb(skb);
		struct sockaddr_nfc_llcp *sockaddr =
			(struct sockaddr_nfc_llcp *) msg->msg_name;

		msg->msg_namelen = sizeof(struct sockaddr_nfc_llcp);
 
 		pr_debug("Datagram socket %d %d\n", ui_cb->dsap, ui_cb->ssap);
 
 		sockaddr->sa_family = AF_NFC;
 		sockaddr->nfc_protocol = NFC_PROTO_NFC_DEP;
 		sockaddr->dsap = ui_cb->dsap;
		sockaddr->ssap = ui_cb->ssap;
	}

	/* Mark read part of skb as used */
	if (!(flags & MSG_PEEK)) {

		/* SOCK_STREAM: re-queue skb if it contains unreceived data */
		if (sk->sk_type == SOCK_STREAM ||
		    sk->sk_type == SOCK_DGRAM ||
		    sk->sk_type == SOCK_RAW) {
			skb_pull(skb, copied);
			if (skb->len) {
				skb_queue_head(&sk->sk_receive_queue, skb);
				goto done;
			}
		}

		kfree_skb(skb);
	}

	/* XXX Queue backlogged skbs */

done:
	/* SOCK_SEQPACKET: return real length if MSG_TRUNC is set */
	if (sk->sk_type == SOCK_SEQPACKET && (flags & MSG_TRUNC))
		copied = rlen;

	return copied;
}

Vulnerability Type: +Info 
CWE ID: CWE-200
Summary: The llcp_sock_recvmsg function in net/nfc/llcp/sock.c in the Linux kernel before 3.9-rc7 does not initialize a certain length variable and a certain data structure, which allows local users to obtain sensitive information from kernel stack memory via a crafted recvmsg or recvfrom system call.
Commit Message: NFC: llcp: fix info leaks via msg_name in llcp_sock_recvmsg()

The code in llcp_sock_recvmsg() does not initialize all the members of
struct sockaddr_nfc_llcp when filling the sockaddr info. Nor does it
initialize the padding bytes of the structure inserted by the compiler
for alignment.

Also, if the socket is in state LLCP_CLOSED or is shutting down during
receive the msg_namelen member is not updated to 0 while otherwise
returning with 0, i.e. "success". The msg_namelen update is also
missing for stream and seqpacket sockets which don't fill the sockaddr
info.

Both issues lead to the fact that the code will leak uninitialized
kernel stack bytes in net/socket.c.

Fix the first issue by initializing the memory used for sockaddr info
with memset(0). Fix the second one by setting msg_namelen to 0 early.
It will be updated later if we're going to fill the msg_name member.

Cc: Lauro Ramos Venancio <lauro.venancio@openbossa.org>
Cc: Aloisio Almeida Jr <aloisio.almeida@openbossa.org>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>