Code: static int dgram_recvmsg(struct kiocb *iocb, struct sock *sk,
		struct msghdr *msg, size_t len, int noblock, int flags,
		int *addr_len)
{
	size_t copied = 0;
	int err = -EOPNOTSUPP;
	struct sk_buff *skb;
	struct sockaddr_ieee802154 *saddr;

	saddr = (struct sockaddr_ieee802154 *)msg->msg_name;

	skb = skb_recv_datagram(sk, flags, noblock, &err);
	if (!skb)
		goto out;

	copied = skb->len;
	if (len < copied) {
		msg->msg_flags |= MSG_TRUNC;
		copied = len;
	}

	/* FIXME: skip headers if necessary ?! */
	err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied);
	if (err)
		goto done;

	sock_recv_ts_and_drops(msg, sk, skb);

 	if (saddr) {
 		saddr->family = AF_IEEE802154;
 		saddr->addr = mac_cb(skb)->sa;
	}
	if (addr_len)
 		*addr_len = sizeof(*saddr);
 
 	if (flags & MSG_TRUNC)
 		copied = skb->len;
done:
	skb_free_datagram(sk, skb);
out:
	if (err)
		return err;
	return copied;
}

Vulnerability Type: +Info 
CWE ID: CWE-200
Summary: The dgram_recvmsg function in net/ieee802154/dgram.c in the Linux kernel before 3.12.4 updates a certain length value without ensuring that an associated data structure has been initialized, which allows local users to obtain sensitive information from kernel stack memory via a (1) recvfrom, (2) recvmmsg, or (3) recvmsg system call.
Commit Message: inet: prevent leakage of uninitialized memory to user in recv syscalls

Only update *addr_len when we actually fill in sockaddr, otherwise we
can return uninitialized memory from the stack to the caller in the
recvfrom, recvmmsg and recvmsg syscalls. Drop the the (addr_len == NULL)
checks because we only get called with a valid addr_len pointer either
from sock_common_recvmsg or inet_recvmsg.

If a blocking read waits on a socket which is concurrently shut down we
now return zero and set msg_msgnamelen to 0.

Reported-by: mpb <mpb.mail@gmail.com>
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>