[PATCH 1/2] KEYS: Add key_type keyagent

[Benjamin Coddington]

Define and register a new key_type called keyagent.  When instantiated,
keyagent keys take a reference on the struct pid of the current task, and
store a number between SIGRTMIN and SIGRTMAX.

In a later patch, we'll use that number to send a realtime signal to the
keyagent task in order to answer request-key callouts for other key types.

Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
---
 security/keys/Kconfig    |  9 +++++
 security/keys/Makefile   |  1 +
 security/keys/keyagent.c | 73 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 83 insertions(+)
 create mode 100644 security/keys/keyagent.c

diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index abb03a1b2a5c..f31a0f94ca88 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -112,6 +112,15 @@ config USER_DECRYPTED_DATA
 
 	  If you are unsure as to whether this is required, answer N.
 
+config KEYAGENT
+	bool "KEYAGENT"
+	depends on KEYS
+	help
+	  This option allows persistent userland processes to answer
+	  request-key callouts.
+
+	  If you are unsure as to whether this is required, answer N.
+
 config KEY_DH_OPERATIONS
        bool "Diffie-Hellman operations on retained keys"
        depends on KEYS
diff --git a/security/keys/Makefile b/security/keys/Makefile
index 5f40807f05b3..c753f8f79c38 100644
--- a/security/keys/Makefile
+++ b/security/keys/Makefile
@@ -23,6 +23,7 @@ obj-$(CONFIG_SYSCTL) += sysctl.o
 obj-$(CONFIG_PERSISTENT_KEYRINGS) += persistent.o
 obj-$(CONFIG_KEY_DH_OPERATIONS) += dh.o
 obj-$(CONFIG_ASYMMETRIC_KEY_TYPE) += keyctl_pkey.o
+obj-$(CONFIG_KEYAGENT) += keyagent.o
 
 #
 # Key types
diff --git a/security/keys/keyagent.c b/security/keys/keyagent.c
new file mode 100644
index 000000000000..87ebfe00c710
--- /dev/null
+++ b/security/keys/keyagent.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Key Agent handling
+ *
+ * Copyright (C) 2022 Red Hat Inc. All Rights Reserved.
+ * Written by Benjamin Coddington (bcodding@xxxxxxxxxx)
+ */
+
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/key.h>
+#include <linux/key-type.h>
+
+#include <keys/user-type.h>
+
+/*
+ * Keyagent key payload.
+ */
+struct keyagent {
+	struct pid *pid;
+	int sig;
+};
+
+/*
+ * Instantiate takes a reference to the current task's struct pid
+ * and the requested realtime signal number.
+ */
+static int
+keyagent_instantiate(struct key *key, struct key_preparsed_payload *prep)
+{
+	struct keyagent *ka;
+	__be16 sig = *(__be16 *)prep->data;
+
+	/* Only real-time signals numbers allowed */
+	if (sig < SIGRTMIN || sig > SIGRTMAX)
+		return -EINVAL;
+
+	ka = kzalloc(sizeof(struct keyagent), GFP_KERNEL);
+	if (!ka)
+		return -ENOMEM;
+
+	ka->pid = get_task_pid(current, PIDTYPE_PID);
+	ka->sig = sig;
+	key->payload.data[0] = ka;
+
+	return 0;
+}
+
+static void keyagent_destroy(struct key *key)
+{
+	struct keyagent *ka = key->payload.data[0];
+
+	put_pid(ka->pid);
+	kfree(ka);
+}
+
+/*
+ * keyagent keys represent userland processes waiting on signals from the
+ * kernel to respond to request-key callouts
+ */
+struct key_type key_type_keyagent = {
+	.name			= "keyagent",
+	.instantiate	= keyagent_instantiate,
+	.def_datalen	= sizeof(struct keyagent),
+	.destroy		= keyagent_destroy,
+	.describe		= user_describe,
+};
+
+static int __init keyagent_init(void)
+{
+	return register_key_type(&key_type_keyagent);
+}
+
+late_initcall(keyagent_init);
-- 
2.31.1