On Wed, 2019-10-23 at 16:39 -0700, Lakshmi Ramasubramanian wrote:
> Added an ima policy hook BUILTIN_TRUSTED_KEYS to measure keys added
> to builtin_trusted_keys keyring.
>
> Added a helper function to check if the given keyring is
> the builtin_trusted_keys keyring.
>
> Defined a function to map the keyring to ima policy hook function
> and use it when measuring the key.
.builtin_trusted_keys is a trusted keyring, which is created by the
kernel. It cannot be deleted or replaced by userspace, so it should
be possible to correlate a keyring name with a keyring number on
policy load.
Other examples of trusted keyrings are: .ima, .evm, .platform,
.blacklist, .builtin_regdb_keys. Instead of defining a keyring
specific method of getting the keyring number, define a generic
method. For example, the userspace command "keyctl describe
%keyring:.builtin_trusted_keys" searches /proc/keys, but the kernel
shouldn't need to access /proc/keys.
>
> Signed-off-by: Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx>
> ---
> Documentation/ABI/testing/ima_policy | 1 +
> certs/system_keyring.c | 5 +++++
> include/keys/system_keyring.h | 2 ++
> security/integrity/ima/ima.h | 2 ++
> security/integrity/ima/ima_api.c | 1 +
> security/integrity/ima/ima_main.c | 25 +++++++++++++++++++++++--
> security/integrity/ima/ima_queue.c | 2 +-
> 7 files changed, 35 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index fc376a323908..25566c74e679 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -29,6 +29,7 @@ Description:
> [FIRMWARE_CHECK]
> [KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
> [KEXEC_CMDLINE]
> + [BUILTIN_TRUSTED_KEYS]
The .builtin_trusted_keys is the name of a keyring, not of an IMA
hook. Define a new IMA policy "keyring=" option, where keyring is
optional. Some IMA policy rules might look like:
# measure all keys
measure func=KEYRING_CHECK
# measure keys on the IMA keyring
measure func=KEYRING_CHECK keyring=".ima"
# measure keys on the BUILTIN and IMA keyrings into a different PCR
measure func=KEYRING_CHECK keyring=".builtin_trusted_keys|.ima" pcr=11
> mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
> [[^]MAY_EXEC]
> fsmagic:= hex value
>
>
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index bce430b3386e..986f80eead4d 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -605,6 +605,24 @@ int ima_load_data(enum kernel_load_data_id id)
> return 0;
> }
>
> +/*
> + * Maps the given keyring to a IMA Hook.
> + * @keyring: A keyring to which a key maybe linked to.
> + *
> + * This function currently handles only builtin_trusted_keys.
> + * To handle more keyrings, this function, ima hook and
> + * ima policy handler need to be updated.
> + */
> +static enum ima_hooks keyring_policy_map(struct key *keyring)
> +{
> + enum ima_hooks func = NONE;
> +
> + if (is_builtin_trusted_keyring(keyring))
> + func = BUILTIN_TRUSTED_KEYS;
> +
> + return func;
> +}
> +
> /*
> * process_buffer_measurement - Measure the buffer to ima log.
> * @buf: pointer to the buffer that needs to be added to the log.
> @@ -706,19 +724,22 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
> unsigned long flags, bool create)
> {
> const struct public_key *pk;
> + enum ima_hooks func;
>
> if (key->type != &key_type_asymmetric)
> return;
>
> + func = keyring_policy_map(keyring);
> +
"func", in this case, should be something like "KEYRING_CHECK". No
mapping is necessary.
> if (!ima_initialized) {
> - ima_queue_key_for_measurement(key, NONE);
> + ima_queue_key_for_measurement(key, func);
> return;
> }
>
> pk = key->payload.data[asym_crypto];
> process_buffer_measurement(pk->key, pk->keylen,
> key->description,
> - NONE, 0);
> + func, 0);
Pass the "keyring" to process_buffer_measurement() and on to
ima_get_action(), so that ima_get_action() determines whether the
keyring is in policy.
Mimi
> }
>
