rxrpc: Don't expose skbs to in-kernel users [ver #2]

Don't expose skbs to in-kernel users, such as the AFS filesystem, but
instead provide a notification hook the indicates that a call needs
attention and another that indicates that there's a new call to be
collected.

This makes the following possibilities more achievable:

 (1) Call refcounting can be made simpler if skbs don't hold refs to calls.

 (2) skbs referring to non-data events will be able to be freed much sooner
     rather than being queued for AFS to pick up as rxrpc_kernel_recv_data
     will be able to consult the call state.

 (3) We can shortcut the receive phase when a call is remotely aborted
     because we don't have to go through all the packets to get to the one
     cancelling the operation.

 (4) It makes it easier to do encryption/decryption directly between AFS's
     buffers and sk_buffs.

 (5) Encryption/decryption can more easily be done in the AFS's thread
     contexts - usually that of the userspace process that issued a syscall
     - rather than in one of rxrpc's background threads on a workqueue.

 (6) AFS will be able to wait synchronously on a call inside AF_RXRPC.

To make this work, the following interface function has been added:

     int rxrpc_kernel_recv_data(
		struct socket *sock, struct rxrpc_call *call,
		void *buffer, size_t bufsize, size_t *_offset,
		bool want_more, u32 *_abort_code);

This is the recvmsg equivalent.  It allows the caller to find out about the
state of a specific call and to transfer received data into a buffer
piecemeal.

afs_extract_data() and rxrpc_kernel_recv_data() now do all the extraction
logic between them.  They don't wait synchronously yet because the socket
lock needs to be dealt with.

Five interface functions have been removed:

	rxrpc_kernel_is_data_last()
    	rxrpc_kernel_get_abort_code()
    	rxrpc_kernel_get_error_number()
    	rxrpc_kernel_free_skb()
    	rxrpc_kernel_data_consumed()

As a temporary hack, sk_buffs going to an in-kernel call are queued on the
rxrpc_call struct (->knlrecv_queue) rather than being handed over to the
in-kernel user.  To process the queue internally, a temporary function,
temp_deliver_data() has been added.  This will be replaced with common code
between the rxrpc_recvmsg() path and the kernel_rxrpc_recv_data() path in a
future patch.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 4 deletions

diff --git a/net/rxrpc/call_accept.c b/net/rxrpc/call_accept.c
index 03af88fe798b..68a439e30df1 100644
--- a/net/rxrpc/call_accept.c
+++ b/net/rxrpc/call_accept.c
@@ -286,7 +286,8 @@ security_mismatch:
  * - assign the user call ID to the call at the front of the queue
  */
 struct rxrpc_call *rxrpc_accept_call(struct rxrpc_sock *rx,
-				     unsigned long user_call_ID)
+				     unsigned long user_call_ID,
+				     rxrpc_notify_rx_t notify_rx)
 {
 	struct rxrpc_call *call;
 	struct rb_node *parent, **pp;
@@ -340,6 +341,7 @@ struct rxrpc_call *rxrpc_accept_call(struct rxrpc_sock *rx,
 	}
 
 	/* formalise the acceptance */
+	call->notify_rx = notify_rx;
 	call->user_call_ID = user_call_ID;
 	rb_link_node(&call->sock_node, parent, pp);
 	rb_insert_color(&call->sock_node, &rx->calls);
@@ -437,17 +439,20 @@ out:
  * rxrpc_kernel_accept_call - Allow a kernel service to accept an incoming call
  * @sock: The socket on which the impending call is waiting
  * @user_call_ID: The tag to attach to the call
+ * @notify_rx: Where to send notifications instead of socket queue
  *
  * Allow a kernel service to accept an incoming call, assuming the incoming
- * call is still valid.
+ * call is still valid.  The caller should immediately trigger their own
+ * notification as there must be data waiting.
  */
 struct rxrpc_call *rxrpc_kernel_accept_call(struct socket *sock,
-					    unsigned long user_call_ID)
+					    unsigned long user_call_ID,
+					    rxrpc_notify_rx_t notify_rx)
 {
 	struct rxrpc_call *call;
 
 	_enter(",%lx", user_call_ID);
-	call = rxrpc_accept_call(rxrpc_sk(sock->sk), user_call_ID);
+	call = rxrpc_accept_call(rxrpc_sk(sock->sk), user_call_ID, notify_rx);
 	_leave(" = %p", call);
 	return call;
 }