Re: [PATCH v2] IMA: Add audit log for failure conditions

Mimi Zohar
2020-06-08T11:53:01Z

Hi Lakshmi,

On Sun, 2020-06-07 at 15:14 -0700, Lakshmi Ramasubramanian wrote:
> The final log statement in process_buffer_measurement() for failure
> condition is at debug level. This does not log the message unless
> the system log level is raised which would significantly increase
> the messages in the system log. Change this log message to an audit
> message for better triaging failures in the function.
>
> ima_alloc_key_entry() does not log a message for failure condition.
> Add an audit message for failure condition in this function.
>
> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>

Audit messages should be at a higher level.  For example,
"hashing_error", "collect_data", "invalid_pcr".  In the "invalid_pcr"
case, the audit log contains the reason - "ToMToU" or "open_writers" -
as to why the measurement list doesn't match the PCR.

Here you would want "measuring_keys", "measuring_boot_cmdline" with
the reason it failed, not the function name
"process_buffer_measurement".

Userspace needs to be aware of the new audit messages.  Maybe include
samples of them in the cover letter.

thanks,

Mimi

> ---
> security/integrity/ima/ima_main.c | 17 ++++++++++++-----
> security/integrity/ima/ima_queue_keys.c | 4 ++++
> 2 files changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 800fb3bba418..1225198fceb1 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -739,6 +739,7 @@ void process_buffer_measurement(const void *buf, int size,
> int pcr, const char *keyring)
> {
> int ret = 0;
> + const char *audit_cause = "ENOMEM";
> struct ima_template_entry *entry = NULL;
> struct integrity_iint_cache iint = {};
> struct ima_event_data event_data = {.iint = &iint,
> @@ -793,21 +794,27 @@ void process_buffer_measurement(const void *buf, int size,
> iint.ima_hash->length = hash_digest_size[ima_hash_algo];
>
> ret = ima_calc_buffer_hash(buf, size, iint.ima_hash);
> - if (ret < 0)
> + if (ret < 0) {
> + audit_cause = "calc_buffer_hash";
> goto out;
> + }
>
> ret = ima_alloc_init_template(&event_data, &entry, template);
> - if (ret < 0)
> + if (ret < 0) {
> + audit_cause = "alloc_init_template";
> goto out;
> + }
>
> ret = ima_store_template(entry, violation, NULL, buf, pcr);
> -
> - if (ret < 0)
> + if (ret < 0) {
> + audit_cause = "store_template";
> ima_free_template_entry(entry);
> + }
>
> out:
> if (ret < 0)
> - pr_devel("%s: failed, result: %d\n", __func__, ret);
> + integrity_audit_msg(AUDIT_INTEGRITY_PCR, NULL, eventname,
> + __func__, audit_cause, ret, 0);
>
> return;
> }
> diff --git a/security/integrity/ima/ima_queue_keys.c b/security/integrity/ima/ima_queue_keys.c
> index cb3e3f501593..fa606ce68f87 100644
> --- a/security/integrity/ima/ima_queue_keys.c
> +++ b/security/integrity/ima/ima_queue_keys.c
> @@ -68,6 +68,7 @@ static struct ima_key_entry *ima_alloc_key_entry(struct key *keyring,
> size_t payload_len)
> {
> int rc = 0;
> + const char *audit_cause = "ENOMEM";
> struct ima_key_entry *entry;
>
> entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> @@ -88,6 +89,9 @@ static struct ima_key_entry *ima_alloc_key_entry(struct key *keyring,
>
> out:
> if (rc) {
> + integrity_audit_msg(AUDIT_INTEGRITY_PCR, NULL,
> + keyring->description, __func__,
> + audit_cause, rc, 0);
> ima_free_key_entry(entry);
> entry = NULL;
> }