certs: Move load_system_certificate_list to a common function

Move functionality within load_system_certificate_list to a common
function, so it can be reused in the future.

DH Changes:
 - Added inclusion of common.h to common.c (Eric [1]).

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: keyrings@vger.kernel.org
Link: https://lore.kernel.org/r/EDA280F9-F72D-4181-93C7-CDBE95976FF7@oracle.com/ [1]
Link: https://lore.kernel.org/r/20200930201508.35113-2-eric.snowberg@oracle.com/
Link: https://lore.kernel.org/r/20210122181054.32635-3-eric.snowberg@oracle.com/ # v5
Link: https://lore.kernel.org/r/161428672825.677100.7545516389752262918.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/161433311696.902181.3599366124784670368.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161529605850.163428.7786675680201528556.stgit@warthog.procyon.org.uk/ # v3

certs/Makefile

@@ -3,7 +3,7 @@
 # Makefile for the linux kernel signature checking certificates.
 #
 
-obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o
+obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o common.o
 obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist.o
 ifneq ($(CONFIG_SYSTEM_BLACKLIST_HASH_LIST),"")
 obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist_hashes.o

certs/common.c

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/kernel.h>
+#include <linux/key.h>
+#include "common.h"
+
+int load_certificate_list(const u8 cert_list[],
+			  const unsigned long list_size,
+			  const struct key *keyring)
+{
+	key_ref_t key;
+	const u8 *p, *end;
+	size_t plen;
+
+	p = cert_list;
+	end = p + list_size;
+	while (p < end) {
+		/* Each cert begins with an ASN.1 SEQUENCE tag and must be more
+		 * than 256 bytes in size.
+		 */
+		if (end - p < 4)
+			goto dodgy_cert;
+		if (p[0] != 0x30 &&
+		    p[1] != 0x82)
+			goto dodgy_cert;
+		plen = (p[2] << 8) | p[3];
+		plen += 4;
+		if (plen > end - p)
+			goto dodgy_cert;
+
+		key = key_create_or_update(make_key_ref(keyring, 1),
+					   "asymmetric",
+					   NULL,
+					   p,
+					   plen,
+					   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
+					   KEY_USR_VIEW | KEY_USR_READ),
+					   KEY_ALLOC_NOT_IN_QUOTA |
+					   KEY_ALLOC_BUILT_IN |
+					   KEY_ALLOC_BYPASS_RESTRICTION);
+		if (IS_ERR(key)) {
+			pr_err("Problem loading in-kernel X.509 certificate (%ld)\n",
+			       PTR_ERR(key));
+		} else {
+			pr_notice("Loaded X.509 cert '%s'\n",
+				  key_ref_to_ptr(key)->description);
+			key_ref_put(key);
+		}
+		p += plen;
+	}
+
+	return 0;
+
+dodgy_cert:
+	pr_err("Problem parsing in-kernel X.509 certificate list\n");
+	return 0;
+}

certs/common.h

@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _CERT_COMMON_H
+#define _CERT_COMMON_H
+
+int load_certificate_list(const u8 cert_list[], const unsigned long list_size,
+			  const struct key *keyring);
+
+#endif

certs/system_keyring.c

@@ -16,6 +16,7 @@
 #include <keys/asymmetric-type.h>
 #include <keys/system_keyring.h>
 #include <crypto/pkcs7.h>
+#include "common.h"
 
 static struct key *builtin_trusted_keys;
 #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
@@ -137,54 +138,10 @@ device_initcall(system_trusted_keyring_init);
  */
 static __init int load_system_certificate_list(void)
 {
-	key_ref_t key;
-	const u8 *p, *end;
-	size_t plen;
-
 	pr_notice("Loading compiled-in X.509 certificates\n");
 
-	p = system_certificate_list;
-	end = p + system_certificate_list_size;
-	while (p < end) {
-		/* Each cert begins with an ASN.1 SEQUENCE tag and must be more
-		 * than 256 bytes in size.
-		 */
-		if (end - p < 4)
-			goto dodgy_cert;
-		if (p[0] != 0x30 &&
-		    p[1] != 0x82)
-			goto dodgy_cert;
-		plen = (p[2] << 8) | p[3];
-		plen += 4;
-		if (plen > end - p)
-			goto dodgy_cert;
-
-		key = key_create_or_update(make_key_ref(builtin_trusted_keys, 1),
-					   "asymmetric",
-					   NULL,
-					   p,
-					   plen,
-					   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
-					   KEY_USR_VIEW | KEY_USR_READ),
-					   KEY_ALLOC_NOT_IN_QUOTA |
-					   KEY_ALLOC_BUILT_IN |
-					   KEY_ALLOC_BYPASS_RESTRICTION);
-		if (IS_ERR(key)) {
-			pr_err("Problem loading in-kernel X.509 certificate (%ld)\n",
-			       PTR_ERR(key));
-		} else {
-			pr_notice("Loaded X.509 cert '%s'\n",
-				  key_ref_to_ptr(key)->description);
-			key_ref_put(key);
-		}
-		p += plen;
-	}
-
-	return 0;
-
-dodgy_cert:
-	pr_err("Problem parsing in-kernel X.509 certificate list\n");
-	return 0;
+	return load_certificate_list(system_certificate_list, system_certificate_list_size,
+				     builtin_trusted_keys);
 }
 late_initcall(load_system_certificate_list);