irda: Fix missing msg_namelen update in irda_recvmsg_dgram()

commit 5ae94c0d upstream.

The current code does not fill the msg_name member in case it is set.
It also does not set the msg_namelen member to 0 and therefore makes
net/socket.c leak the local, uninitialized sockaddr_storage variable
to userland -- 128 bytes of kernel stack memory.

Fix that by simply setting msg_namelen to 0 as obviously nobody cared
about irda_recvmsg_dgram() not filling the msg_name in case it was
set.

Cc: Samuel Ortiz <samuel@sortiz.org>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[dannf: adjusted to apply to Debian's 2.6.32]
Signed-off-by: Willy Tarreau <w@1wt.eu>

net/irda/af_irda.c

@@ -1338,6 +1338,8 @@ static int irda_recvmsg_dgram(struct kiocb *iocb, struct socket *sock,
 	if ((err = sock_error(sk)) < 0)
 		return err;
 
+	msg->msg_namelen = 0;
+
 	skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT,
 				flags & MSG_DONTWAIT, &err);
 	if (!skb)