[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both

Provide AF_RXRPC sockets that can be used to talk to AFS servers, or serve
answers to AFS clients.  KerberosIV security is fully supported.  The patches
and some example test programs can be found in:

	http://people.redhat.com/~dhowells/rxrpc/

This will eventually replace the old implementation of kernel-only RxRPC
currently resident in net/rxrpc/.

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

1 files changed, 791 insertions, 0 deletions

diff --git a/net/rxrpc/ar-input.c b/net/rxrpc/ar-input.c
new file mode 100644
index 00000000000..323c3454561
--- /dev/null
+++ b/net/rxrpc/ar-input.c
@@ -0,0 +1,791 @@
+/* RxRPC packet reception
+ *
+ * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/module.h>
+#include <linux/net.h>
+#include <linux/skbuff.h>
+#include <linux/errqueue.h>
+#include <linux/udp.h>
+#include <linux/in.h>
+#include <linux/in6.h>
+#include <linux/icmp.h>
+#include <net/sock.h>
+#include <net/af_rxrpc.h>
+#include <net/ip.h>
+#include "ar-internal.h"
+
+unsigned long rxrpc_ack_timeout = 1;
+
+const char *rxrpc_pkts[] = {
+	"?00",
+	"DATA", "ACK", "BUSY", "ABORT", "ACKALL", "CHALL", "RESP", "DEBUG",
+	"?09", "?10", "?11", "?12", "?13", "?14", "?15"
+};
+
+/*
+ * queue a packet for recvmsg to pass to userspace
+ * - the caller must hold a lock on call->lock
+ * - must not be called with interrupts disabled (sk_filter() disables BH's)
+ * - eats the packet whether successful or not
+ * - there must be just one reference to the packet, which the caller passes to
+ *   this function
+ */
+int rxrpc_queue_rcv_skb(struct rxrpc_call *call, struct sk_buff *skb,
+			bool force, bool terminal)
+{
+	struct rxrpc_skb_priv *sp;
+	struct sock *sk;
+	int skb_len, ret;
+
+	_enter(",,%d,%d", force, terminal);
+
+	ASSERT(!irqs_disabled());
+
+	sp = rxrpc_skb(skb);
+	ASSERTCMP(sp->call, ==, call);
+
+	/* if we've already posted the terminal message for a call, then we
+	 * don't post any more */
+	if (test_bit(RXRPC_CALL_TERMINAL_MSG, &call->flags)) {
+		_debug("already terminated");
+		ASSERTCMP(call->state, >=, RXRPC_CALL_COMPLETE);
+		skb->destructor = NULL;
+		sp->call = NULL;
+		rxrpc_put_call(call);
+		rxrpc_free_skb(skb);
+		return 0;
+	}
+
+	sk = &call->socket->sk;
+
+	if (!force) {
+		/* cast skb->rcvbuf to unsigned...  It's pointless, but
+		 * reduces number of warnings when compiling with -W
+		 * --ANK */
+//		ret = -ENOBUFS;
+//		if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
+//		    (unsigned) sk->sk_rcvbuf)
+//			goto out;
+
+		ret = sk_filter(sk, skb);
+		if (ret < 0)
+			goto out;
+	}
+
+	spin_lock_bh(&sk->sk_receive_queue.lock);
+	if (!test_bit(RXRPC_CALL_TERMINAL_MSG, &call->flags) &&
+	    !test_bit(RXRPC_CALL_RELEASED, &call->flags) &&
+	    call->socket->sk.sk_state != RXRPC_CLOSE) {
+		skb->destructor = rxrpc_packet_destructor;
+		skb->dev = NULL;
+		skb->sk = sk;
+		atomic_add(skb->truesize, &sk->sk_rmem_alloc);
+
+		/* Cache the SKB length before we tack it onto the receive
+		 * queue.  Once it is added it no longer belongs to us and
+		 * may be freed by other threads of control pulling packets
+		 * from the queue.
+		 */
+		skb_len = skb->len;
+
+		_net("post skb %p", skb);
+		__skb_queue_tail(&sk->sk_receive_queue, skb);
+		spin_unlock_bh(&sk->sk_receive_queue.lock);
+
+		if (!sock_flag(sk, SOCK_DEAD))
+			sk->sk_data_ready(sk, skb_len);
+
+		if (terminal) {
+			_debug("<<<< TERMINAL MESSAGE >>>>");
+			set_bit(RXRPC_CALL_TERMINAL_MSG, &call->flags);
+		}
+
+		skb = NULL;
+	} else {
+		spin_unlock_bh(&sk->sk_receive_queue.lock);
+	}
+	ret = 0;
+
+out:
+	/* release the socket buffer */
+	if (skb) {
+		skb->destructor = NULL;
+		sp->call = NULL;
+		rxrpc_put_call(call);
+		rxrpc_free_skb(skb);
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * process a DATA packet, posting the packet to the appropriate queue
+ * - eats the packet if successful
+ */
+static int rxrpc_fast_process_data(struct rxrpc_call *call,
+				   struct sk_buff *skb, u32 seq)
+{
+	struct rxrpc_skb_priv *sp;
+	bool terminal;
+	int ret, ackbit, ack;
+
+	_enter("{%u,%u},,{%u}", call->rx_data_post, call->rx_first_oos, seq);
+
+	sp = rxrpc_skb(skb);
+	ASSERTCMP(sp->call, ==, NULL);
+
+	spin_lock(&call->lock);
+
+	if (call->state > RXRPC_CALL_COMPLETE)
+		goto discard;
+
+	ASSERTCMP(call->rx_data_expect, >=, call->rx_data_post);
+	ASSERTCMP(call->rx_data_post, >=, call->rx_data_recv);
+	ASSERTCMP(call->rx_data_recv, >=, call->rx_data_eaten);
+
+	if (seq < call->rx_data_post) {
+		_debug("dup #%u [-%u]", seq, call->rx_data_post);
+		ack = RXRPC_ACK_DUPLICATE;
+		ret = -ENOBUFS;
+		goto discard_and_ack;
+	}
+
+	/* we may already have the packet in the out of sequence queue */
+	ackbit = seq - (call->rx_data_eaten + 1);
+	ASSERTCMP(ackbit, >=, 0);
+	if (__test_and_set_bit(ackbit, &call->ackr_window)) {
+		_debug("dup oos #%u [%u,%u]",
+		       seq, call->rx_data_eaten, call->rx_data_post);
+		ack = RXRPC_ACK_DUPLICATE;
+		goto discard_and_ack;
+	}
+
+	if (seq >= call->ackr_win_top) {
+		_debug("exceed #%u [%u]", seq, call->ackr_win_top);
+		__clear_bit(ackbit, &call->ackr_window);
+		ack = RXRPC_ACK_EXCEEDS_WINDOW;
+		goto discard_and_ack;
+	}
+
+	if (seq == call->rx_data_expect) {
+		clear_bit(RXRPC_CALL_EXPECT_OOS, &call->flags);
+		call->rx_data_expect++;
+	} else if (seq > call->rx_data_expect) {
+		_debug("oos #%u [%u]", seq, call->rx_data_expect);
+		call->rx_data_expect = seq + 1;
+		if (test_and_set_bit(RXRPC_CALL_EXPECT_OOS, &call->flags)) {
+			ack = RXRPC_ACK_OUT_OF_SEQUENCE;
+			goto enqueue_and_ack;
+		}
+		goto enqueue_packet;
+	}
+
+	if (seq != call->rx_data_post) {
+		_debug("ahead #%u [%u]", seq, call->rx_data_post);
+		goto enqueue_packet;
+	}
+
+	if (test_bit(RXRPC_CALL_RCVD_LAST, &call->flags))
+		goto protocol_error;
+
+	/* if the packet need security things doing to it, then it goes down
+	 * the slow path */
+	if (call->conn->security)
+		goto enqueue_packet;
+
+	sp->call = call;
+	rxrpc_get_call(call);
+	terminal = ((sp->hdr.flags & RXRPC_LAST_PACKET) &&
+		    !(sp->hdr.flags & RXRPC_CLIENT_INITIATED));
+	ret = rxrpc_queue_rcv_skb(call, skb, false, terminal);
+	if (ret < 0) {
+		if (ret == -ENOMEM || ret == -ENOBUFS) {
+			__clear_bit(ackbit, &call->ackr_window);
+			ack = RXRPC_ACK_NOSPACE;
+			goto discard_and_ack;
+		}
+		goto out;
+	}
+
+	skb = NULL;
+
+	_debug("post #%u", seq);
+	ASSERTCMP(call->rx_data_post, ==, seq);
+	call->rx_data_post++;
+
+	if (sp->hdr.flags & RXRPC_LAST_PACKET)
+		set_bit(RXRPC_CALL_RCVD_LAST, &call->flags);
+
+	/* if we've reached an out of sequence packet then we need to drain
+	 * that queue into the socket Rx queue now */
+	if (call->rx_data_post == call->rx_first_oos) {
+		_debug("drain rx oos now");
+		read_lock(&call->state_lock);
+		if (call->state < RXRPC_CALL_COMPLETE &&
+		    !test_and_set_bit(RXRPC_CALL_DRAIN_RX_OOS, &call->events))
+			schedule_work(&call->processor);
+		read_unlock(&call->state_lock);
+	}
+
+	spin_unlock(&call->lock);
+	atomic_inc(&call->ackr_not_idle);
+	rxrpc_propose_ACK(call, RXRPC_ACK_DELAY, sp->hdr.serial, false);
+	_leave(" = 0 [posted]");
+	return 0;
+
+protocol_error:
+	ret = -EBADMSG;
+out:
+	spin_unlock(&call->lock);
+	_leave(" = %d", ret);
+	return ret;
+
+discard_and_ack:
+	_debug("discard and ACK packet %p", skb);
+	__rxrpc_propose_ACK(call, ack, sp->hdr.serial, true);
+discard:
+	spin_unlock(&call->lock);
+	rxrpc_free_skb(skb);
+	_leave(" = 0 [discarded]");
+	return 0;
+
+enqueue_and_ack:
+	__rxrpc_propose_ACK(call, ack, sp->hdr.serial, true);
+enqueue_packet:
+	_net("defer skb %p", skb);
+	spin_unlock(&call->lock);
+	skb_queue_tail(&call->rx_queue, skb);
+	atomic_inc(&call->ackr_not_idle);
+	read_lock(&call->state_lock);
+	if (call->state < RXRPC_CALL_DEAD)
+		schedule_work(&call->processor);
+	read_unlock(&call->state_lock);
+	_leave(" = 0 [queued]");
+	return 0;
+}
+
+/*
+ * assume an implicit ACKALL of the transmission phase of a client socket upon
+ * reception of the first reply packet
+ */
+static void rxrpc_assume_implicit_ackall(struct rxrpc_call *call, u32 serial)
+{
+	write_lock_bh(&call->state_lock);
+
+	switch (call->state) {
+	case RXRPC_CALL_CLIENT_AWAIT_REPLY:
+		call->state = RXRPC_CALL_CLIENT_RECV_REPLY;
+		call->acks_latest = serial;
+
+		_debug("implicit ACKALL %%%u", call->acks_latest);
+		set_bit(RXRPC_CALL_RCVD_ACKALL, &call->events);
+		write_unlock_bh(&call->state_lock);
+
+		if (try_to_del_timer_sync(&call->resend_timer) >= 0) {
+			clear_bit(RXRPC_CALL_RESEND_TIMER, &call->events);
+			clear_bit(RXRPC_CALL_RESEND, &call->events);
+			clear_bit(RXRPC_CALL_RUN_RTIMER, &call->flags);
+		}
+		break;
+
+	default:
+		write_unlock_bh(&call->state_lock);
+		break;
+	}
+}
+
+/*
+ * post an incoming packet to the nominated call to deal with
+ * - must get rid of the sk_buff, either by freeing it or by queuing it
+ */
+void rxrpc_fast_process_packet(struct rxrpc_call *call, struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	__be32 _abort_code;
+	u32 serial, hi_serial, seq, abort_code;
+
+	_enter("%p,%p", call, skb);
+
+	ASSERT(!irqs_disabled());
+
+#if 0 // INJECT RX ERROR
+	if (sp->hdr.type == RXRPC_PACKET_TYPE_DATA) {
+		static int skip = 0;
+		if (++skip == 3) {
+			printk("DROPPED 3RD PACKET!!!!!!!!!!!!!\n");
+			skip = 0;
+			goto free_packet;
+		}
+	}
+#endif
+
+	/* track the latest serial number on this connection for ACK packet
+	 * information */
+	serial = ntohl(sp->hdr.serial);
+	hi_serial = atomic_read(&call->conn->hi_serial);
+	while (serial > hi_serial)
+		hi_serial = atomic_cmpxchg(&call->conn->hi_serial, hi_serial,
+					   serial);
+
+	/* request ACK generation for any ACK or DATA packet that requests
+	 * it */
+	if (sp->hdr.flags & RXRPC_REQUEST_ACK) {
+		_proto("ACK Requested on %%%u", serial);
+		rxrpc_propose_ACK(call, RXRPC_ACK_REQUESTED, sp->hdr.serial,
+				  !(sp->hdr.flags & RXRPC_MORE_PACKETS));
+	}
+
+	switch (sp->hdr.type) {
+	case RXRPC_PACKET_TYPE_ABORT:
+		_debug("abort");
+
+		if (skb_copy_bits(skb, 0, &_abort_code,
+				  sizeof(_abort_code)) < 0)
+			goto protocol_error;
+
+		abort_code = ntohl(_abort_code);
+		_proto("Rx ABORT %%%u { %x }", serial, abort_code);
+
+		write_lock_bh(&call->state_lock);
+		if (call->state < RXRPC_CALL_COMPLETE) {
+			call->state = RXRPC_CALL_REMOTELY_ABORTED;
+			call->abort_code = abort_code;
+			set_bit(RXRPC_CALL_RCVD_ABORT, &call->events);
+			schedule_work(&call->processor);
+		}
+		goto free_packet_unlock;
+
+	case RXRPC_PACKET_TYPE_BUSY:
+		_proto("Rx BUSY %%%u", serial);
+
+		if (call->conn->out_clientflag)
+			goto protocol_error;
+
+		write_lock_bh(&call->state_lock);
+		switch (call->state) {
+		case RXRPC_CALL_CLIENT_SEND_REQUEST:
+			call->state = RXRPC_CALL_SERVER_BUSY;
+			set_bit(RXRPC_CALL_RCVD_BUSY, &call->events);
+			schedule_work(&call->processor);
+		case RXRPC_CALL_SERVER_BUSY:
+			goto free_packet_unlock;
+		default:
+			goto protocol_error_locked;
+		}
+
+	default:
+		_proto("Rx %s %%%u", rxrpc_pkts[sp->hdr.type], serial);
+		goto protocol_error;
+
+	case RXRPC_PACKET_TYPE_DATA:
+		seq = ntohl(sp->hdr.seq);
+
+		_proto("Rx DATA %%%u { #%u }", serial, seq);
+
+		if (seq == 0)
+			goto protocol_error;
+
+		call->ackr_prev_seq = sp->hdr.seq;
+
+		/* received data implicitly ACKs all of the request packets we
+		 * sent when we're acting as a client */
+		if (call->state == RXRPC_CALL_CLIENT_AWAIT_REPLY)
+			rxrpc_assume_implicit_ackall(call, serial);
+
+		switch (rxrpc_fast_process_data(call, skb, seq)) {
+		case 0:
+			skb = NULL;
+			goto done;
+
+		default:
+			BUG();
+
+			/* data packet received beyond the last packet */
+		case -EBADMSG:
+			goto protocol_error;
+		}
+
+	case RXRPC_PACKET_TYPE_ACK:
+		/* ACK processing is done in process context */
+		read_lock_bh(&call->state_lock);
+		if (call->state < RXRPC_CALL_DEAD) {
+			skb_queue_tail(&call->rx_queue, skb);
+			schedule_work(&call->processor);
+			skb = NULL;
+		}
+		read_unlock_bh(&call->state_lock);
+		goto free_packet;
+	}
+
+protocol_error:
+	_debug("protocol error");
+	write_lock_bh(&call->state_lock);
+protocol_error_locked:
+	if (call->state <= RXRPC_CALL_COMPLETE) {
+		call->state = RXRPC_CALL_LOCALLY_ABORTED;
+		call->abort_code = RX_PROTOCOL_ERROR;
+		set_bit(RXRPC_CALL_ABORT, &call->events);
+		schedule_work(&call->processor);
+	}
+free_packet_unlock:
+	write_unlock_bh(&call->state_lock);
+free_packet:
+	rxrpc_free_skb(skb);
+done:
+	_leave("");
+}
+
+/*
+ * split up a jumbo data packet
+ */
+static void rxrpc_process_jumbo_packet(struct rxrpc_call *call,
+				       struct sk_buff *jumbo)
+{
+	struct rxrpc_jumbo_header jhdr;
+	struct rxrpc_skb_priv *sp;
+	struct sk_buff *part;
+
+	_enter(",{%u,%u}", jumbo->data_len, jumbo->len);
+
+	sp = rxrpc_skb(jumbo);
+
+	do {
+		sp->hdr.flags &= ~RXRPC_JUMBO_PACKET;
+
+		/* make a clone to represent the first subpacket in what's left
+		 * of the jumbo packet */
+		part = skb_clone(jumbo, GFP_ATOMIC);
+		if (!part) {
+			/* simply ditch the tail in the event of ENOMEM */
+			pskb_trim(jumbo, RXRPC_JUMBO_DATALEN);
+			break;
+		}
+		rxrpc_new_skb(part);
+
+		pskb_trim(part, RXRPC_JUMBO_DATALEN);
+
+		if (!pskb_pull(jumbo, RXRPC_JUMBO_DATALEN))
+			goto protocol_error;
+
+		if (skb_copy_bits(jumbo, 0, &jhdr, sizeof(jhdr)) < 0)
+			goto protocol_error;
+		if (!pskb_pull(jumbo, sizeof(jhdr)))
+			BUG();
+
+		sp->hdr.seq	= htonl(ntohl(sp->hdr.seq) + 1);
+		sp->hdr.serial	= htonl(ntohl(sp->hdr.serial) + 1);
+		sp->hdr.flags	= jhdr.flags;
+		sp->hdr._rsvd	= jhdr._rsvd;
+
+		_proto("Rx DATA Jumbo %%%u", ntohl(sp->hdr.serial) - 1);
+
+		rxrpc_fast_process_packet(call, part);
+		part = NULL;
+
+	} while (sp->hdr.flags & RXRPC_JUMBO_PACKET);
+
+	rxrpc_fast_process_packet(call, jumbo);
+	_leave("");
+	return;
+
+protocol_error:
+	_debug("protocol error");
+	rxrpc_free_skb(part);
+	rxrpc_free_skb(jumbo);
+	write_lock_bh(&call->state_lock);
+	if (call->state <= RXRPC_CALL_COMPLETE) {
+		call->state = RXRPC_CALL_LOCALLY_ABORTED;
+		call->abort_code = RX_PROTOCOL_ERROR;
+		set_bit(RXRPC_CALL_ABORT, &call->events);
+		schedule_work(&call->processor);
+	}
+	write_unlock_bh(&call->state_lock);
+	_leave("");
+}
+
+/*
+ * post an incoming packet to the appropriate call/socket to deal with
+ * - must get rid of the sk_buff, either by freeing it or by queuing it
+ */
+static void rxrpc_post_packet_to_call(struct rxrpc_connection *conn,
+				      struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp;
+	struct rxrpc_call *call;
+	struct rb_node *p;
+	__be32 call_id;
+
+	_enter("%p,%p", conn, skb);
+
+	read_lock_bh(&conn->lock);
+
+	sp = rxrpc_skb(skb);
+
+	/* look at extant calls by channel number first */
+	call = conn->channels[ntohl(sp->hdr.cid) & RXRPC_CHANNELMASK];
+	if (!call || call->call_id != sp->hdr.callNumber)
+		goto call_not_extant;
+
+	_debug("extant call [%d]", call->state);
+	ASSERTCMP(call->conn, ==, conn);
+
+	read_lock(&call->state_lock);
+	switch (call->state) {
+	case RXRPC_CALL_LOCALLY_ABORTED:
+		if (!test_and_set_bit(RXRPC_CALL_ABORT, &call->events))
+			schedule_work(&call->processor);
+	case RXRPC_CALL_REMOTELY_ABORTED:
+	case RXRPC_CALL_NETWORK_ERROR:
+	case RXRPC_CALL_DEAD:
+		goto free_unlock;
+	default:
+		break;
+	}
+
+	read_unlock(&call->state_lock);
+	rxrpc_get_call(call);
+	read_unlock_bh(&conn->lock);
+
+	if (sp->hdr.type == RXRPC_PACKET_TYPE_DATA &&
+	    sp->hdr.flags & RXRPC_JUMBO_PACKET)
+		rxrpc_process_jumbo_packet(call, skb);
+	else
+		rxrpc_fast_process_packet(call, skb);
+
+	rxrpc_put_call(call);
+	goto done;
+
+call_not_extant:
+	/* search the completed calls in case what we're dealing with is
+	 * there */
+	_debug("call not extant");
+
+	call_id = sp->hdr.callNumber;
+	p = conn->calls.rb_node;
+	while (p) {
+		call = rb_entry(p, struct rxrpc_call, conn_node);
+
+		if (call_id < call->call_id)
+			p = p->rb_left;
+		else if (call_id > call->call_id)
+			p = p->rb_right;
+		else
+			goto found_completed_call;
+	}
+
+dead_call:
+	/* it's a either a really old call that we no longer remember or its a
+	 * new incoming call */
+	read_unlock_bh(&conn->lock);
+
+	if (sp->hdr.flags & RXRPC_CLIENT_INITIATED &&
+	    sp->hdr.seq == __constant_cpu_to_be32(1)) {
+		_debug("incoming call");
+		skb_queue_tail(&conn->trans->local->accept_queue, skb);
+		schedule_work(&conn->trans->local->acceptor);
+		goto done;
+	}
+
+	_debug("dead call");
+	skb->priority = RX_CALL_DEAD;
+	rxrpc_reject_packet(conn->trans->local, skb);
+	goto done;
+
+	/* resend last packet of a completed call
+	 * - client calls may have been aborted or ACK'd
+	 * - server calls may have been aborted
+	 */
+found_completed_call:
+	_debug("completed call");
+
+	if (atomic_read(&call->usage) == 0)
+		goto dead_call;
+
+	/* synchronise any state changes */
+	read_lock(&call->state_lock);
+	ASSERTIFCMP(call->state != RXRPC_CALL_CLIENT_FINAL_ACK,
+		    call->state, >=, RXRPC_CALL_COMPLETE);
+
+	if (call->state == RXRPC_CALL_LOCALLY_ABORTED ||
+	    call->state == RXRPC_CALL_REMOTELY_ABORTED ||
+	    call->state == RXRPC_CALL_DEAD) {
+		read_unlock(&call->state_lock);
+		goto dead_call;
+	}
+
+	if (call->conn->in_clientflag) {
+		read_unlock(&call->state_lock);
+		goto dead_call; /* complete server call */
+	}
+
+	_debug("final ack again");
+	rxrpc_get_call(call);
+	set_bit(RXRPC_CALL_ACK_FINAL, &call->events);
+	schedule_work(&call->processor);
+
+free_unlock:
+	read_unlock(&call->state_lock);
+	read_unlock_bh(&conn->lock);
+	rxrpc_free_skb(skb);
+done:
+	_leave("");
+}
+
+/*
+ * post connection-level events to the connection
+ * - this includes challenges, responses and some aborts
+ */
+static void rxrpc_post_packet_to_conn(struct rxrpc_connection *conn,
+				      struct sk_buff *skb)
+{
+	_enter("%p,%p", conn, skb);
+
+	atomic_inc(&conn->usage);
+	skb_queue_tail(&conn->rx_queue, skb);
+	schedule_work(&conn->processor);
+}
+
+/*
+ * handle data received on the local endpoint
+ * - may be called in interrupt context
+ */
+void rxrpc_data_ready(struct sock *sk, int count)
+{
+	struct rxrpc_connection *conn;
+	struct rxrpc_transport *trans;
+	struct rxrpc_skb_priv *sp;
+	struct rxrpc_local *local;
+	struct rxrpc_peer *peer;
+	struct sk_buff *skb;
+	int ret;
+
+	_enter("%p, %d", sk, count);
+
+	ASSERT(!irqs_disabled());
+
+	read_lock_bh(&rxrpc_local_lock);
+	local = sk->sk_user_data;
+	if (local && atomic_read(&local->usage) > 0)
+		rxrpc_get_local(local);
+	else
+		local = NULL;
+	read_unlock_bh(&rxrpc_local_lock);
+	if (!local) {
+		_leave(" [local dead]");
+		return;
+	}
+
+	skb = skb_recv_datagram(sk, 0, 1, &ret);
+	if (!skb) {
+		rxrpc_put_local(local);
+		if (ret == -EAGAIN)
+			return;
+		_debug("UDP socket error %d", ret);
+		return;
+	}
+
+	rxrpc_new_skb(skb);
+
+	_net("recv skb %p", skb);
+
+	/* we'll probably need to checksum it (didn't call sock_recvmsg) */
+	if (skb_checksum_complete(skb)) {
+		rxrpc_free_skb(skb);
+		rxrpc_put_local(local);
+		_leave(" [CSUM failed]");
+		return;
+	}
+
+	/* the socket buffer we have is owned by UDP, with UDP's data all over
+	 * it, but we really want our own */
+	skb_orphan(skb);
+	sp = rxrpc_skb(skb);
+	memset(sp, 0, sizeof(*sp));
+
+	_net("Rx UDP packet from %08x:%04hu",
+	     ntohl(ip_hdr(skb)->saddr), ntohs(udp_hdr(skb)->source));
+
+	/* dig out the RxRPC connection details */
+	if (skb_copy_bits(skb, sizeof(struct udphdr), &sp->hdr,
+			  sizeof(sp->hdr)) < 0)
+		goto bad_message;
+	if (!pskb_pull(skb, sizeof(struct udphdr) + sizeof(sp->hdr)))
+		BUG();
+
+	_net("Rx RxRPC %s ep=%x call=%x:%x",
+	     sp->hdr.flags & RXRPC_CLIENT_INITIATED ? "ToServer" : "ToClient",
+	     ntohl(sp->hdr.epoch),
+	     ntohl(sp->hdr.cid),
+	     ntohl(sp->hdr.callNumber));
+
+	if (sp->hdr.type == 0 || sp->hdr.type >= RXRPC_N_PACKET_TYPES) {
+		_proto("Rx Bad Packet Type %u", sp->hdr.type);
+		goto bad_message;
+	}
+
+	if (sp->hdr.type == RXRPC_PACKET_TYPE_DATA &&
+	    (sp->hdr.callNumber == 0 || sp->hdr.seq == 0))
+		goto bad_message;
+
+	peer = rxrpc_find_peer(local, ip_hdr(skb)->saddr, udp_hdr(skb)->source);
+	if (IS_ERR(peer))
+		goto cant_route_call;
+
+	trans = rxrpc_find_transport(local, peer);
+	rxrpc_put_peer(peer);
+	if (!trans)
+		goto cant_route_call;
+
+	conn = rxrpc_find_connection(trans, &sp->hdr);
+	rxrpc_put_transport(trans);
+	if (!conn)
+		goto cant_route_call;
+
+	_debug("CONN %p {%d}", conn, conn->debug_id);
+
+	if (sp->hdr.callNumber == 0)
+		rxrpc_post_packet_to_conn(conn, skb);
+	else
+		rxrpc_post_packet_to_call(conn, skb);
+	rxrpc_put_connection(conn);
+	rxrpc_put_local(local);
+	return;
+
+cant_route_call:
+	_debug("can't route call");
+	if (sp->hdr.flags & RXRPC_CLIENT_INITIATED &&
+	    sp->hdr.type == RXRPC_PACKET_TYPE_DATA) {
+		if (sp->hdr.seq == __constant_cpu_to_be32(1)) {
+			_debug("first packet");
+			skb_queue_tail(&local->accept_queue, skb);
+			schedule_work(&local->acceptor);
+			rxrpc_put_local(local);
+			_leave(" [incoming]");
+			return;
+		}
+		skb->priority = RX_INVALID_OPERATION;
+	} else {
+		skb->priority = RX_CALL_DEAD;
+	}
+
+	_debug("reject");
+	rxrpc_reject_packet(local, skb);
+	rxrpc_put_local(local);
+	_leave(" [no call]");
+	return;
+
+bad_message:
+	skb->priority = RX_PROTOCOL_ERROR;
+	rxrpc_reject_packet(local, skb);
+	rxrpc_put_local(local);
+	_leave(" [badmsg]");
+}