[PATCH v3 08/10] integrity: Use root of trust signature restriction

Eric Snowberg
2022-12-14T00:35:35Z

Keys added to the IMA keyring must be vouched for by keys contained
within the builtin or secondary keyrings. These keys must also be
endorsed as or by a CA. The CA qualifications include having the CA bit
and the keyCertSign KeyUsage bit set. Or they could be validated by a
properly formed intermediate certificate as long as it was signed by a
qualifying CA. Currently these restrictions are not enforced. Use the
new restrict_link_by_ca_builtin_and_secondary_trusted and
restrict_link_by_ca_builtin_trusted to enforce the missing CA
restrictions when adding keys to the IMA keyring. With the CA restrictions
enforced, allow the machine keyring to be enabled with
IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
security/integrity/Kconfig | 1 -
security/integrity/digsig.c | 4 ++--
security/integrity/ima/Kconfig | 6 +++---
3 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig
index 599429f99f99..14cc3c767270 100644
--- a/security/integrity/Kconfig
+++ b/security/integrity/Kconfig
@@ -68,7 +68,6 @@ config INTEGRITY_MACHINE_KEYRING
depends on INTEGRITY_ASYMMETRIC_KEYS
depends on SYSTEM_BLACKLIST_KEYRING
depends on LOAD_UEFI_KEYS
- depends on !IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
help
If set, provide a keyring to which Machine Owner Keys (MOK) may
be added. This keyring shall contain just MOK keys. Unlike keys
diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index 8a82a6c7f48a..1fe8d1ed6e0b 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -34,9 +34,9 @@ static const char * const keyring_name[INTEGRITY_KEYRING_MAX] = {
};

#ifdef CONFIG_IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
-#define restrict_link_to_ima restrict_link_by_builtin_and_secondary_trusted
+#define restrict_link_to_ima restrict_link_by_ca_builtin_and_secondary_trusted
#else
-#define restrict_link_to_ima restrict_link_by_builtin_trusted
+#define restrict_link_to_ima restrict_link_by_ca_builtin_trusted
#endif

static struct key *integrity_keyring_from_id(const unsigned int id)
diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 7249f16257c7..6fe3bd0e5c82 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -269,13 +269,13 @@ config IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
default n
help
Keys may be added to the IMA or IMA blacklist keyrings, if the
- key is validly signed by a CA cert in the system built-in or
- secondary trusted keyrings.
+ key is validly signed by a CA cert in the system built-in,
+ secondary trusted, or machine keyrings.

Intermediate keys between those the kernel has compiled in and the
IMA keys to be added may be added to the system secondary keyring,
provided they are validly signed by a key already resident in the
- built-in or secondary trusted keyrings.
+ built-in, secondary trusted or machine keyrings.

config IMA_BLACKLIST_KEYRING
bool "Create IMA machine owner blacklist keyrings (EXPERIMENTAL)"
--
2.27.0