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Subject[PATCH v1a 2/2] KEYS: validate certificate trust only with builtin keys
Date
Instead of allowing public keys, with certificates signed by any
key on the system trusted keyring, to be added to a trusted keyring,
this patch further restricts the certificates to those signed only by
builtin keys on the system keyring.

This patch defines a new option 'builtin' for the kernel parameter
'keys_ownerid' to allow trust validation using builtin keys.

Idea belongs to Mimi Zohar.

Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
---
Documentation/kernel-parameters.txt | 2 +-
crypto/asymmetric_keys/x509_public_key.c | 9 +++++++--
include/linux/key.h | 1 +
kernel/system_keyring.c | 1 +
4 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 7a810d3..336dabe 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1437,7 +1437,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
keys_ownerid=[KEYS] This parameter identifies a specific key(s) on
the system trusted keyring to be used for certificate
trust validation.
- format: id:<keyid>
+ format: { id:<keyid> | builtin }

kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
Format: <Controller#>[,poll interval]
diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
index d46b790..c3805a8 100644
--- a/crypto/asymmetric_keys/x509_public_key.c
+++ b/crypto/asymmetric_keys/x509_public_key.c
@@ -24,6 +24,7 @@
#include "public_key.h"
#include "x509_parser.h"

+static bool builtin_keys;
static char *owner_keyid;
static int __init default_owner_keyid_set(char *str)
{
@@ -32,6 +33,8 @@ static int __init default_owner_keyid_set(char *str)

if (strncmp(str, "id:", 3) == 0)
owner_keyid = str; /* owner local key 'id:xxxxxx' */
+ else if (strcmp(str, "builtin") == 0)
+ builtin_keys = true;

return 1;
}
@@ -197,8 +200,10 @@ static int x509_validate_trust(struct x509_certificate *cert,
cert->authority,
strlen(cert->authority));
if (!IS_ERR(key)) {
- pk = key->payload.data;
- ret = x509_check_signature(pk, cert);
+ if (!builtin_keys || test_bit(KEY_FLAG_BUILTIN, &key->flags)) {
+ pk = key->payload.data;
+ ret = x509_check_signature(pk, cert);
+ }
key_put(key);
}
return ret;
diff --git a/include/linux/key.h b/include/linux/key.h
index cd0abb8..67c8e7e 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -170,6 +170,7 @@ struct key {
#define KEY_FLAG_INVALIDATED 7 /* set if key has been invalidated */
#define KEY_FLAG_TRUSTED 8 /* set if key is trusted */
#define KEY_FLAG_TRUSTED_ONLY 9 /* set if keyring only accepts links to trusted keys */
+#define KEY_FLAG_BUILTIN 10 /* set if key is builtin */

/* the key type and key description string
* - the desc is used to match a key against search criteria
diff --git a/kernel/system_keyring.c b/kernel/system_keyring.c
index 52ebc70..875f64e 100644
--- a/kernel/system_keyring.c
+++ b/kernel/system_keyring.c
@@ -89,6 +89,7 @@ static __init int load_system_certificate_list(void)
pr_err("Problem loading in-kernel X.509 certificate (%ld)\n",
PTR_ERR(key));
} else {
+ set_bit(KEY_FLAG_BUILTIN, &key_ref_to_ptr(key)->flags);
pr_notice("Loaded X.509 cert '%s'\n",
key_ref_to_ptr(key)->description);
key_ref_put(key);
--
1.9.1


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