Code: int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
		 size_t len, int noblock, int flags, int *addr_len)
 {
 	struct inet_sock *isk = inet_sk(sk);
 	int family = sk->sk_family;
	struct sockaddr_in *sin;
	struct sockaddr_in6 *sin6;
 	struct sk_buff *skb;
 	int copied, err;
 
	pr_debug("ping_recvmsg(sk=%p,sk->num=%u)\n", isk, isk->inet_num);

	err = -EOPNOTSUPP;
 	if (flags & MSG_OOB)
 		goto out;
 
	if (addr_len) {
		if (family == AF_INET)
			*addr_len = sizeof(*sin);
		else if (family == AF_INET6 && addr_len)
			*addr_len = sizeof(*sin6);
	}
 	if (flags & MSG_ERRQUEUE) {
 		if (family == AF_INET) {
 			return ip_recv_error(sk, msg, len);
#if IS_ENABLED(CONFIG_IPV6)
		} else if (family == AF_INET6) {
			return pingv6_ops.ipv6_recv_error(sk, msg, len);
#endif
		}
	}

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

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

	/* Don't bother checking the checksum */
	err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied);
	if (err)
		goto done;

	sock_recv_timestamp(msg, sk, skb);
 
 	/* Copy the address and add cmsg data. */
 	if (family == AF_INET) {
		sin = (struct sockaddr_in *) msg->msg_name;
 		sin->sin_family = AF_INET;
 		sin->sin_port = 0 /* skb->h.uh->source */;
 		sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
 		memset(sin->sin_zero, 0, sizeof(sin->sin_zero));
 
 		if (isk->cmsg_flags)
 			ip_cmsg_recv(msg, skb);

#if IS_ENABLED(CONFIG_IPV6)
 	} else if (family == AF_INET6) {
 		struct ipv6_pinfo *np = inet6_sk(sk);
 		struct ipv6hdr *ip6 = ipv6_hdr(skb);
		sin6 = (struct sockaddr_in6 *) msg->msg_name;
 		sin6->sin6_family = AF_INET6;
 		sin6->sin6_port = 0;
 		sin6->sin6_addr = ip6->saddr;
 		sin6->sin6_flowinfo = 0;
 		if (np->sndflow)
 			sin6->sin6_flowinfo = ip6_flowinfo(ip6);
 
 		sin6->sin6_scope_id = ipv6_iface_scope_id(&sin6->sin6_addr,
 							  IP6CB(skb)->iif);
 
 		if (inet6_sk(sk)->rxopt.all)
 			pingv6_ops.ip6_datagram_recv_ctl(sk, msg, skb);
#endif
	} else {
		BUG();
	}

	err = copied;

done:
	skb_free_datagram(sk, skb);
out:
	pr_debug("ping_recvmsg -> %d\n", err);
	return err;
}

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>