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Date:   Thu, 10 Dec 2020 16:14:17 -0600
From:   Tyler Hicks <tyhicks@linux.microsoft.com>
To:     Tushar Sugandhi <tusharsu@linux.microsoft.com>
Cc:     zohar@linux.ibm.com, stephen.smalley.work@gmail.com,
        casey@schaufler-ca.com, agk@redhat.com, snitzer@redhat.com,
        gmazyland@gmail.com, paul@paul-moore.com, sashal@kernel.org,
        jmorris@namei.org, nramas@linux.microsoft.com,
        linux-integrity@vger.kernel.org, selinux@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, dm-devel@redhat.com
Subject: Re: [PATCH v7 1/8] IMA: generalize keyring specific measurement
 constructs
Message-ID: <20201210221417.GF489768@sequoia>
References: <20201209194212.5131-1-tusharsu@linux.microsoft.com>
 <20201209194212.5131-2-tusharsu@linux.microsoft.com>
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In-Reply-To: <20201209194212.5131-2-tusharsu@linux.microsoft.com>
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On 2020-12-09 11:42:05, Tushar Sugandhi wrote:
> IMA functions such as ima_match_keyring(), process_buffer_measurement(),
> ima_match_policy() etc. handle data specific to keyrings. Currently,
> these constructs are not generic to handle any func specific data.
> This makes it harder to extend them without code duplication.
> 
> Refactor the keyring specific measurement constructs to be generic and
> reusable in other measurement scenarios.
> 
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>

I've got a few code cleanup suggestions to ima_match_rule_data() below
but the current patch is fine:

Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>

> ---
>  security/integrity/ima/ima.h        |  6 ++--
>  security/integrity/ima/ima_api.c    |  6 ++--
>  security/integrity/ima/ima_main.c   |  6 ++--
>  security/integrity/ima/ima_policy.c | 49 ++++++++++++++++++-----------
>  4 files changed, 40 insertions(+), 27 deletions(-)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 8e8b1e3cb847..e5622ce8cbb1 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -256,7 +256,7 @@ static inline void ima_process_queued_keys(void) {}
>  int ima_get_action(struct inode *inode, const struct cred *cred, u32 secid,
>  		   int mask, enum ima_hooks func, int *pcr,
>  		   struct ima_template_desc **template_desc,
> -		   const char *keyring);
> +		   const char *func_data);
>  int ima_must_measure(struct inode *inode, int mask, enum ima_hooks func);
>  int ima_collect_measurement(struct integrity_iint_cache *iint,
>  			    struct file *file, void *buf, loff_t size,
> @@ -268,7 +268,7 @@ void ima_store_measurement(struct integrity_iint_cache *iint, struct file *file,
>  			   struct ima_template_desc *template_desc);
>  void process_buffer_measurement(struct inode *inode, const void *buf, int size,
>  				const char *eventname, enum ima_hooks func,
> -				int pcr, const char *keyring);
> +				int pcr, const char *func_data);
>  void ima_audit_measurement(struct integrity_iint_cache *iint,
>  			   const unsigned char *filename);
>  int ima_alloc_init_template(struct ima_event_data *event_data,
> @@ -284,7 +284,7 @@ const char *ima_d_path(const struct path *path, char **pathbuf, char *filename);
>  int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
>  		     enum ima_hooks func, int mask, int flags, int *pcr,
>  		     struct ima_template_desc **template_desc,
> -		     const char *keyring);
> +		     const char *func_data);
>  void ima_init_policy(void);
>  void ima_update_policy(void);
>  void ima_update_policy_flag(void);
> diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
> index 4f39fb93f278..af218babd198 100644
> --- a/security/integrity/ima/ima_api.c
> +++ b/security/integrity/ima/ima_api.c
> @@ -170,7 +170,7 @@ void ima_add_violation(struct file *file, const unsigned char *filename,
>   * @func: caller identifier
>   * @pcr: pointer filled in if matched measure policy sets pcr=
>   * @template_desc: pointer filled in if matched measure policy sets template=
> - * @keyring: keyring name used to determine the action
> + * @func_data: private data specific to @func, can be NULL.
>   *
>   * The policy is defined in terms of keypairs:
>   *		subj=, obj=, type=, func=, mask=, fsmagic=
> @@ -186,14 +186,14 @@ void ima_add_violation(struct file *file, const unsigned char *filename,
>  int ima_get_action(struct inode *inode, const struct cred *cred, u32 secid,
>  		   int mask, enum ima_hooks func, int *pcr,
>  		   struct ima_template_desc **template_desc,
> -		   const char *keyring)
> +		   const char *func_data)
>  {
>  	int flags = IMA_MEASURE | IMA_AUDIT | IMA_APPRAISE | IMA_HASH;
>  
>  	flags &= ima_policy_flag;
>  
>  	return ima_match_policy(inode, cred, secid, func, mask, flags, pcr,
> -				template_desc, keyring);
> +				template_desc, func_data);
>  }
>  
>  /*
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 68956e884403..e76ef4bfd0f4 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -786,13 +786,13 @@ int ima_post_load_data(char *buf, loff_t size,
>   * @eventname: event name to be used for the buffer entry.
>   * @func: IMA hook
>   * @pcr: pcr to extend the measurement
> - * @keyring: keyring name to determine the action to be performed
> + * @func_data: private data specific to @func, can be NULL.
>   *
>   * Based on policy, the buffer is measured into the ima log.
>   */
>  void process_buffer_measurement(struct inode *inode, const void *buf, int size,
>  				const char *eventname, enum ima_hooks func,
> -				int pcr, const char *keyring)
> +				int pcr, const char *func_data)
>  {
>  	int ret = 0;
>  	const char *audit_cause = "ENOMEM";
> @@ -831,7 +831,7 @@ void process_buffer_measurement(struct inode *inode, const void *buf, int size,
>  	if (func) {
>  		security_task_getsecid(current, &secid);
>  		action = ima_get_action(inode, current_cred(), secid, 0, func,
> -					&pcr, &template, keyring);
> +					&pcr, &template, func_data);
>  		if (!(action & IMA_MEASURE))
>  			return;
>  	}
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 823a0c1379cb..25419c7ff50b 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -453,30 +453,44 @@ int ima_lsm_policy_change(struct notifier_block *nb, unsigned long event,
>  }
>  
>  /**
> - * ima_match_keyring - determine whether the keyring matches the measure rule
> - * @rule: a pointer to a rule
> - * @keyring: name of the keyring to match against the measure rule
> + * ima_match_rule_data - determine whether the given func_data matches
> + *			 the measure rule data
> + * @rule: IMA policy rule
> + * @func_data: data to match against the measure rule data
>   * @cred: a pointer to a credentials structure for user validation
>   *
> - * Returns true if keyring matches one in the rule, false otherwise.
> + * Returns true if func_data matches one in the rule, false otherwise.
>   */
> -static bool ima_match_keyring(struct ima_rule_entry *rule,
> -			      const char *keyring, const struct cred *cred)
> +static bool ima_match_rule_data(struct ima_rule_entry *rule,
> +				const char *func_data,
> +				const struct cred *cred)
>  {
> +	const struct ima_rule_opt_list *opt_list = NULL;
>  	bool matched = false;
>  	size_t i;
>  
>  	if ((rule->flags & IMA_UID) && !rule->uid_op(cred->uid, rule->uid))
>  		return false;
>  
> -	if (!rule->keyrings)
> -		return true;
> +	switch (rule->func) {
> +	case KEY_CHECK:
> +		if (!rule->keyrings)
> +			return true;
> +		else
> +			opt_list = rule->keyrings;

You return if rule->keyrings is NULL so drop this else and simply make
the opt_list assignment.

> +		break;
> +	default:
> +		break;

I would like to see the 'return false;' happen immediately here instead
of waiting for the opt_list check below.

> +	}
>  
> -	if (!keyring)
> +	if (!func_data)
> +		return false;
> +
> +	if (!opt_list)
>  		return false;

If you return false in the 'default:' case above, you can just remove this
entire conditional because you'll be assigning opt_list in all of the
valid cases of the switch statement.

Tyler

>  
> -	for (i = 0; i < rule->keyrings->count; i++) {
> -		if (!strcmp(rule->keyrings->items[i], keyring)) {
> +	for (i = 0; i < opt_list->count; i++) {
> +		if (!strcmp(opt_list->items[i], func_data)) {
>  			matched = true;
>  			break;
>  		}
> @@ -493,20 +507,20 @@ static bool ima_match_keyring(struct ima_rule_entry *rule,
>   * @secid: the secid of the task to be validated
>   * @func: LIM hook identifier
>   * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
> - * @keyring: keyring name to check in policy for KEY_CHECK func
> + * @func_data: private data specific to @func, can be NULL.
>   *
>   * Returns true on rule match, false on failure.
>   */
>  static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
>  			    const struct cred *cred, u32 secid,
>  			    enum ima_hooks func, int mask,
> -			    const char *keyring)
> +			    const char *func_data)
>  {
>  	int i;
>  
>  	if (func == KEY_CHECK) {
>  		return (rule->flags & IMA_FUNC) && (rule->func == func) &&
> -		       ima_match_keyring(rule, keyring, cred);
> +			ima_match_rule_data(rule, func_data, cred);
>  	}
>  	if ((rule->flags & IMA_FUNC) &&
>  	    (rule->func != func && func != POST_SETATTR))
> @@ -610,8 +624,7 @@ static int get_subaction(struct ima_rule_entry *rule, enum ima_hooks func)
>   * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
>   * @pcr: set the pcr to extend
>   * @template_desc: the template that should be used for this rule
> - * @keyring: the keyring name, if given, to be used to check in the policy.
> - *           keyring can be NULL if func is anything other than KEY_CHECK.
> + * @func_data: private data specific to @func, can be NULL.
>   *
>   * Measure decision based on func/mask/fsmagic and LSM(subj/obj/type)
>   * conditions.
> @@ -623,7 +636,7 @@ static int get_subaction(struct ima_rule_entry *rule, enum ima_hooks func)
>  int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
>  		     enum ima_hooks func, int mask, int flags, int *pcr,
>  		     struct ima_template_desc **template_desc,
> -		     const char *keyring)
> +		     const char *func_data)
>  {
>  	struct ima_rule_entry *entry;
>  	int action = 0, actmask = flags | (flags << 1);
> @@ -638,7 +651,7 @@ int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
>  			continue;
>  
>  		if (!ima_match_rules(entry, inode, cred, secid, func, mask,
> -				     keyring))
> +				     func_data))
>  			continue;
>  
>  		action |= entry->flags & IMA_ACTION_FLAGS;
> -- 
> 2.17.1
>