On Thursday, September 6 2007 9:04:01 am Tetsuo Handa wrote:
> (1) It uses userspace intervention to allow/reject
> connections and/or packets based on the application's domain.
> Since existent hooks can't be used for this purpose,
> I inserted a new hook post_recv_datagram() at skb_recv_datagram()
> and I modified socket_post_accept() to return error so that
> I can drop/disconnect based on the application's domain.
>
> I think skb_recv_datagram() is the only place that can remove
> a message picked up with MSG_PEEK flags from the receive queue.
> To remove a message picked up with MSG_PEEK flags, I noticed that
> I have to do skb_kill_datagram()-like operation so that
> "the head message that must not be delivered to the caller" won't
> prevent picking up of "the non-head message that should be delivered to the
> caller" when the caller repeats only recv(MSG_PEEK) requests.
> Since skb_recv_datagram() can be called from interrupt context,
> I have to use spin_lock_irqsave() instead for spin_lock_bh(), am I
> right?
There are almost certainly better people to answer locking questions, but here
is my take on it ... If you are accessing data both in a bottom half and
elsewhere you need to make sure you disable bottom halfs from running before
you access the data outside the bottom half (spin_lock_bh()). If you are
accessing data both in an interrupt handler and elsewhere you need to make
sure you disable interrupts when accessing data outside the irq handler
(spin_lock_irqsave()).
> By the way, why can't socket_post_accept() fail?
> Someone may wish to do memory allocation at socket_post_accept().
> socket_accept() is too early for memory allocation because
> there is no chance to free allocated memory
> when sock->ops->accept() failed.
> I think socket_post_accept() should be able to fail.
>From my experience the community disapproves of approaches which go through
the entire TCP handshake and then terminate the connection, which is what
allowing security_socket_post_accept() to fail would do.
--
paul moore
linux security @ hp
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