linux-kernel - Re: [PATCH v2] IMA: Defined timer to free queued keys

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Date:   Tue, 24 Dec 2019 15:35:04 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        James.Bottomley@...senPartnership.com,
        linux-integrity@...r.kernel.org
Cc:     eric.snowberg@...cle.com, dhowells@...hat.com,
        mathew.j.martineau@...ux.intel.com, matthewgarrett@...gle.com,
        sashal@...nel.org, jamorris@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, keyrings@...r.kernel.org
Subject: Re: [PATCH v2] IMA: Defined timer to free queued keys

On Tue, 2019-12-24 at 10:01 -0800, Lakshmi Ramasubramanian wrote:
> keys queued for measurement should be freed if a custom IMA policy
> was not loaded. Otherwise, the keys will remain queued forever
> consuming kernel memory.
> 
> This patch defines a timer to handle the above scenario. The timer
> is setup to expire 5 minutes after IMA initialization is completed.
> 
> If a custom IMA policy is loaded before the timer expires, the timer
> is removed and any queued keys are processed for measurement.
> But if a custom policy was not loaded, on timer expiration
> queued keys are just freed.
> 
> Signed-off-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>

Thanks.  This patch is now queued in next-integrity-testing.

Mimi

> ---
>  security/integrity/ima/ima.h                 |  2 +
>  security/integrity/ima/ima_asymmetric_keys.c | 42 ++++++++++++++++++--
>  security/integrity/ima/ima_init.c            |  8 +++-
>  3 files changed, 48 insertions(+), 4 deletions(-)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 97f8a4078483..c483215a9ee5 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -216,8 +216,10 @@ struct ima_key_entry {
>  	char *keyring_name;
>  };
>  void ima_process_queued_keys(void);
> +void ima_init_key_queue(void);
>  #else
>  static inline void ima_process_queued_keys(void) {}
> +static inline void ima_init_key_queue(void) {}
>  #endif /* CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE */
>  
>  /* LIM API function definitions */
> diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
> index 4124f10ff0c2..9ea2233c911a 100644
> --- a/security/integrity/ima/ima_asymmetric_keys.c
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -11,6 +11,7 @@
>  
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>  
> +#include <linux/timer.h>
>  #include <keys/asymmetric-type.h>
>  #include "ima.h"
>  
> @@ -26,6 +27,36 @@ static bool ima_process_keys;
>  static DEFINE_MUTEX(ima_keys_mutex);
>  static LIST_HEAD(ima_keys);
>  
> +/*
> + * If custom IMA policy is not loaded then keys queued up
> + * for measurement should be freed. This timer is used
> + * for handling this scenario.
> + */
> +static long ima_key_queue_timeout = 300000; /* 5 Minutes */
> +static struct timer_list ima_key_queue_timer;
> +static bool timer_expired;
> +
> +/*
> + * This timer callback function frees keys that may still be
> + * queued up in case custom IMA policy was not loaded.
> + */
> +static void ima_timer_handler(struct timer_list *timer)
> +{
> +	timer_expired = true;
> +	ima_process_queued_keys();
> +}
> +
> +/*
> + * This function sets up a timer to free queued keys in case
> + * custom IMA policy was never loaded.
> + */
> +void ima_init_key_queue(void)
> +{
> +	timer_setup(&ima_key_queue_timer, ima_timer_handler, 0);
> +	mod_timer(&ima_key_queue_timer,
> +		  jiffies + msecs_to_jiffies(ima_key_queue_timeout));
> +}
> +
>  static void ima_free_key_entry(struct ima_key_entry *entry)
>  {
>  	if (entry) {
> @@ -120,10 +151,15 @@ void ima_process_queued_keys(void)
>  	if (!process)
>  		return;
>  
> +	del_timer(&ima_key_queue_timer);
> +
>  	list_for_each_entry_safe(entry, tmp, &ima_keys, list) {
> -		process_buffer_measurement(entry->payload, entry->payload_len,
> -					   entry->keyring_name, KEY_CHECK, 0,
> -					   entry->keyring_name);
> +		if (!timer_expired)
> +			process_buffer_measurement(entry->payload,
> +						   entry->payload_len,
> +						   entry->keyring_name,
> +						   KEY_CHECK, 0,
> +						   entry->keyring_name);
>  		list_del(&entry->list);
>  		ima_free_key_entry(entry);
>  	}
> diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
> index 5d55ade5f3b9..195cb4079b2b 100644
> --- a/security/integrity/ima/ima_init.c
> +++ b/security/integrity/ima/ima_init.c
> @@ -131,5 +131,11 @@ int __init ima_init(void)
>  
>  	ima_init_policy();
>  
> -	return ima_fs_init();
> +	rc = ima_fs_init();
> +	if (rc != 0)
> +		return rc;
> +
> +	ima_init_key_queue();
> +
> +	return rc;
>  }