rxrpc: Allow CHALLENGEs to the passed to the app for a RESPONSE

Allow the app to request that CHALLENGEs be passed to it through an
out-of-band queue that allows recvmsg() to pick it up so that the app can
add data to it with sendmsg().

This will allow the application (AFS or userspace) to interact with the
process if it wants to and put values into user-defined fields.  This will
be used by AFS when talking to a fileserver to supply that fileserver with
a crypto key by which callback RPCs can be encrypted (ie. notifications
from the fileserver to the client).

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
Link: https://patch.msgid.link/20250411095303.2316168-5-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 73 insertions, 0 deletions

diff --git a/fs/afs/cm_security.c b/fs/afs/cm_security.c
new file mode 100644
index 000000000000..efe6a23c8477
--- /dev/null
+++ b/fs/afs/cm_security.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Cache manager security.
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/slab.h>
+#include "internal.h"
+#include "afs_fs.h"
+#include "protocol_yfs.h"
+#define RXRPC_TRACE_ONLY_DEFINE_ENUMS
+#include <trace/events/rxrpc.h>
+
+/*
+ * Respond to an RxGK challenge, adding appdata.
+ */
+static int afs_respond_to_challenge(struct sk_buff *challenge)
+{
+	struct rxrpc_peer *peer;
+	unsigned long peer_data;
+	u16 service_id;
+	u8 security_index;
+
+	rxrpc_kernel_query_challenge(challenge, &peer, &peer_data,
+				     &service_id, &security_index);
+
+	_enter("%u,%u", service_id, security_index);
+
+	switch (service_id) {
+		/* We don't send CM_SERVICE RPCs, so don't expect a challenge
+		 * therefrom.
+		 */
+	case FS_SERVICE:
+	case VL_SERVICE:
+	case YFS_FS_SERVICE:
+	case YFS_VL_SERVICE:
+		break;
+	default:
+		pr_warn("Can't respond to unknown challenge %u:%u",
+			service_id, security_index);
+		return rxrpc_kernel_reject_challenge(challenge, RX_USER_ABORT, -EPROTO,
+						     afs_abort_unsupported_sec_class);
+	}
+
+	switch (security_index) {
+	case RXRPC_SECURITY_RXKAD:
+		return rxkad_kernel_respond_to_challenge(challenge);
+
+	default:
+		return rxrpc_kernel_reject_challenge(challenge, RX_USER_ABORT, -EPROTO,
+						     afs_abort_unsupported_sec_class);
+	}
+}
+
+/*
+ * Process the OOB message queue, processing challenge packets.
+ */
+void afs_process_oob_queue(struct work_struct *work)
+{
+	struct afs_net *net = container_of(work, struct afs_net, rx_oob_work);
+	struct sk_buff *oob;
+	enum rxrpc_oob_type type;
+
+	while ((oob = rxrpc_kernel_dequeue_oob(net->socket, &type))) {
+		switch (type) {
+		case RXRPC_OOB_CHALLENGE:
+			afs_respond_to_challenge(oob);
+			break;
+		}
+		rxrpc_kernel_free_oob(oob);
+	}
+}