linux-kernel - Re: [PATCH 01/12] ima: Have the LSM free its audit rule

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Message-ID: <277dd210-c443-c067-e731-44ac53418fa5@schaufler-ca.com>
Date:   Mon, 22 Jun 2020 17:55:59 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc:     James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        Prakhar Srivastava <prsriva02@...il.com>,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Janne Karhunen <janne.karhunen@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH 01/12] ima: Have the LSM free its audit rule

On 6/22/2020 5:32 PM, Tyler Hicks wrote:
> Ask the LSM to free its audit rule rather than directly calling kfree().
> Both AppArmor and SELinux do additional work in their audit_rule_free()
> hooks. Fix memory leaks by allowing the LSMs to perform necessary work.
>
> Fixes: b16942455193 ("ima: use the lsm policy update notifier")
> Signed-off-by: Tyler Hicks <tyhicks@...ux.microsoft.com>
> Cc: Janne Karhunen <janne.karhunen@...il.com>
> ---
>  security/integrity/ima/ima.h        | 6 ++++++
>  security/integrity/ima/ima_policy.c | 2 +-
>  2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index df93ac258e01..de05d7f1d3ec 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -404,6 +404,7 @@ static inline void ima_free_modsig(struct modsig *modsig)
>  #ifdef CONFIG_IMA_LSM_RULES
>  
>  #define security_filter_rule_init security_audit_rule_init
> +#define security_filter_rule_free security_audit_rule_free
>  #define security_filter_rule_match security_audit_rule_match

In context this seems perfectly reasonable. If, however, you're
working with the LSM infrastructure this set of #defines is maddening.
The existing ones have been driving my nuts for the past few years,
so I'd like to discourage adding another. Since the security_filter_rule
functions are IMA specific they shouldn't be prefixed security_. I know
that it seems to be code churn/bikesheading, but we please change these:

static inline int ima_filter_rule_init(.....)
{
	return security_audit_rule_init(.....);
}

and so forth. I understand if you don't want to make the change.
I have plenty of other things driving me crazy just now, so this
doesn't seem likely to push me over the edge.

>  
>  #else
> @@ -414,6 +415,11 @@ static inline int security_filter_rule_init(u32 field, u32 op, char *rulestr,
>  	return -EINVAL;
>  }
>  
> +static inline void security_filter_rule_free(void *lsmrule)
> +{
> +	return -EINVAL;
> +}
> +
>  static inline int security_filter_rule_match(u32 secid, u32 field, u32 op,
>  					     void *lsmrule)
>  {
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index e493063a3c34..236a731492d1 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -258,7 +258,7 @@ static void ima_lsm_free_rule(struct ima_rule_entry *entry)
>  	int i;
>  
>  	for (i = 0; i < MAX_LSM_RULES; i++) {
> -		kfree(entry->lsm[i].rule);
> +		security_filter_rule_free(entry->lsm[i].rule);
>  		kfree(entry->lsm[i].args_p);
>  	}
>  	kfree(entry);