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

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Date:   Mon, 08 Jun 2020 07:52:51 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        paul@...l-moore.com
Cc:     linux-integrity@...r.kernel.org, linux-audit@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] IMA: Add audit log for failure conditions

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@...ux.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;
>  	}