net: Fix module refcount leak in kernel_accept()

The kernel_accept() does not hold the module refcount of newsock->ops->owner,
so we need __module_get(newsock->ops->owner) code after call kernel_accept()
by hand.
In sunrpc, the module refcount is missing to hold. So this cause kernel panic.

Used following script to reproduct:

while [ 1 ];
do
    mount -t nfs4 192.168.0.19:/ /mnt
    touch /mnt/file
    umount /mnt
    lsmod | grep ipv6
done

This patch fixed the problem by add __module_get(newsock->ops->owner) to
kernel_accept(). So we do not need to used __module_get(newsock->ops->owner)
in every place when used kernel_accept().

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/socket.c

@@ -2307,6 +2307,7 @@ int kernel_accept(struct socket *sock, struct socket **newsock, int flags)
 	}
 
 	(*newsock)->ops = sock->ops;
+	__module_get((*newsock)->ops->owner);
 
 done:
 	return err;