When I proposed a patch in July, I was patching at post-copy_to_user() step
(i.e. after sock_recvmsg()).
This approach messed up user-supplied buffer.
This time, I'm patching at pre-copy_to_user() step
(i.e. at skb_recv_datagram()).
This approach doesn't mess up user-supplied buffer.
I think this is a cleaner way than the previous patch.
Although read() gets an error when select() said "read ready",
I can't find other place to use for accomplishing my goals.
By the way, similar thing can happen when select() against
a file descriptor said "read ready" but read() gets an error
if security policy or security-id of the file has changed
between select() and read(), isn't it?
And such behavior is acceptable, isn't it?
If such behavior can happen and is acceptable and *preferable*,
I think checking permission at dequeue time (i.e. skb_recv_datagram())
is *preferable* way than checking permission at enqueue time
(i.e. socket_sock_rcv_skb()).
Regards.
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