linux-kernel - [PATCH v1 2/3] KEYS: trusted: implement fallback to kernel RNG

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Message-Id: <a5c2a1507cf2bd1b5b6531ce2c0d9d496b8d3d7e.1615914058.git-series.a.fatoum@pengutronix.de>
Date:   Tue, 16 Mar 2021 18:01:17 +0100
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     James Bottomley <jejb@...ux.ibm.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>
Cc:     kernel@...gutronix.de, Ahmad Fatoum <a.fatoum@...gutronix.de>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Horia Geantă <horia.geanta@....com>,
        Aymen Sghaier <aymen.sghaier@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Udit Agarwal <udit.agarwal@....com>,
        Jan Luebbe <j.luebbe@...utronix.de>,
        David Gstir <david@...ma-star.at>,
        Franck LENORMAND <franck.lenormand@....com>,
        Sumit Garg <sumit.garg@...aro.org>, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: [PATCH v1 2/3] KEYS: trusted: implement fallback to kernel RNG

For cases a trusted key source already sources the kernel RNG, we can
use get_random_bytes_wait to get the random data for key material.

Make the get_random callback optional to allow sources to make use of
this.

Signed-off-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
---
To: James Bottomley <jejb@...ux.ibm.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
To: Mimi Zohar <zohar@...ux.ibm.com>
To: David Howells <dhowells@...hat.com>
Cc: James Morris <jmorris@...ei.org>
Cc: "Serge E. Hallyn" <serge@...lyn.com>
Cc: "Horia Geantă" <horia.geanta@....com>
Cc: Aymen Sghaier <aymen.sghaier@....com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Udit Agarwal <udit.agarwal@....com>
Cc: Jan Luebbe <j.luebbe@...utronix.de>
Cc: David Gstir <david@...ma-star.at>
Cc: Franck LENORMAND <franck.lenormand@....com>
Cc: Sumit Garg <sumit.garg@...aro.org>
Cc: keyrings@...r.kernel.org
Cc: linux-crypto@...r.kernel.org
Cc: linux-integrity@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: linux-security-module@...r.kernel.org
---
 include/keys/trusted-type.h               |  2 +-
 security/keys/trusted-keys/trusted_core.c | 11 ++++++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
index d89fa2579ac0..4eb64548a74f 100644
--- a/include/keys/trusted-type.h
+++ b/include/keys/trusted-type.h
@@ -64,7 +64,7 @@ struct trusted_key_ops {
 	/* Unseal a key. */
 	int (*unseal)(struct trusted_key_payload *p, char *datablob);
 
-	/* Get a randomized key. */
+	/* Optional: Get a randomized key. */
 	int (*get_random)(unsigned char *key, size_t key_len);
 
 	/* Exit key interface. */
diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
index ec3a066a4b42..5f92323efedf 100644
--- a/security/keys/trusted-keys/trusted_core.c
+++ b/security/keys/trusted-keys/trusted_core.c
@@ -16,6 +16,7 @@
 #include <linux/key-type.h>
 #include <linux/module.h>
 #include <linux/parser.h>
+#include <linux/random.h>
 #include <linux/rcupdate.h>
 #include <linux/slab.h>
 #include <linux/static_call.h>
@@ -310,8 +311,14 @@ struct key_type key_type_trusted = {
 };
 EXPORT_SYMBOL_GPL(key_type_trusted);
 
+static int kernel_get_random(unsigned char *key, size_t key_len)
+{
+	return get_random_bytes_wait(key, key_len) ?: key_len;
+}
+
 static int __init init_trusted(void)
 {
+	int (*get_random)(unsigned char *key, size_t key_len);
 	int i, ret = 0;
 
 	for (i = 0; i < ARRAY_SIZE(trusted_key_sources); i++) {
@@ -320,6 +327,8 @@ static int __init init_trusted(void)
 			    strlen(trusted_key_sources[i].name)))
 			continue;
 
+		get_random = trusted_key_sources[i].ops->get_random ?: kernel_get_random;
+
 		static_call_update(trusted_key_init,
 				   trusted_key_sources[i].ops->init);
 		static_call_update(trusted_key_seal,
@@ -327,7 +336,7 @@ static int __init init_trusted(void)
 		static_call_update(trusted_key_unseal,
 				   trusted_key_sources[i].ops->unseal);
 		static_call_update(trusted_key_get_random,
-				   trusted_key_sources[i].ops->get_random);
+				   get_random);
 		static_call_update(trusted_key_exit,
 				   trusted_key_sources[i].ops->exit);
 		migratable = trusted_key_sources[i].ops->migratable;
-- 
git-series 0.9.1