Re: [PATCH v39 01/42] integrity: disassociate ima_filter_rule from security_audit_rule

[Roberto Sassu]

On Fri, 2023-12-15 at 14:15 -0800, Casey Schaufler wrote:
> Create real functions for the ima_filter_rule interfaces.
> These replace #defines that obscure the reuse of audit
> interfaces. The new functions are put in security.c because
> they use security module registered hooks that we don't
> want exported.

Beginner question: what makes IMA special, that the audit subsystem
does not need an AUDIT_LSM field to do the same that IMA would do?

In other words, why can't we add the lsm_id parameter to
security_audit_*() functions, so that IMA can just call those?

Thanks

Roberto

> Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
> Reviewed-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> To: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> Cc: linux-integrity@xxxxxxxxxxxxxxx
> ---
>  include/linux/security.h     | 24 ++++++++++++++++++++++++
>  security/integrity/ima/ima.h | 26 --------------------------
>  security/security.c          | 21 +++++++++++++++++++++
>  3 files changed, 45 insertions(+), 26 deletions(-)
> 
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 750130a7b9dd..4790508818ee 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -2009,6 +2009,30 @@ static inline void security_audit_rule_free(void *lsmrule)
>  #endif /* CONFIG_SECURITY */
>  #endif /* CONFIG_AUDIT */
>  
> +#if defined(CONFIG_IMA_LSM_RULES) && defined(CONFIG_SECURITY)
> +int ima_filter_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule);
> +int ima_filter_rule_match(u32 secid, u32 field, u32 op, void *lsmrule);
> +void ima_filter_rule_free(void *lsmrule);
> +
> +#else
> +
> +static inline int ima_filter_rule_init(u32 field, u32 op, char *rulestr,
> +					   void **lsmrule)
> +{
> +	return 0;
> +}
> +
> +static inline int ima_filter_rule_match(u32 secid, u32 field, u32 op,
> +					    void *lsmrule)
> +{
> +	return 0;
> +}
> +
> +static inline void ima_filter_rule_free(void *lsmrule)
> +{ }
> +
> +#endif /* defined(CONFIG_IMA_LSM_RULES) && defined(CONFIG_SECURITY) */
> +
>  #ifdef CONFIG_SECURITYFS
>  
>  extern struct dentry *securityfs_create_file(const char *name, umode_t mode,
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index c29db699c996..560d6104de72 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -420,32 +420,6 @@ static inline void ima_free_modsig(struct modsig *modsig)
>  }
>  #endif /* CONFIG_IMA_APPRAISE_MODSIG */
>  
> -/* LSM based policy rules require audit */
> -#ifdef CONFIG_IMA_LSM_RULES
> -
> -#define ima_filter_rule_init security_audit_rule_init
> -#define ima_filter_rule_free security_audit_rule_free
> -#define ima_filter_rule_match security_audit_rule_match
> -
> -#else
> -
> -static inline int ima_filter_rule_init(u32 field, u32 op, char *rulestr,
> -				       void **lsmrule)
> -{
> -	return -EINVAL;
> -}
> -
> -static inline void ima_filter_rule_free(void *lsmrule)
> -{
> -}
> -
> -static inline int ima_filter_rule_match(u32 secid, u32 field, u32 op,
> -					void *lsmrule)
> -{
> -	return -EINVAL;
> -}
> -#endif /* CONFIG_IMA_LSM_RULES */
> -
>  #ifdef	CONFIG_IMA_READ_POLICY
>  #define	POLICY_FILE_FLAGS	(S_IWUSR | S_IRUSR)
>  #else
> diff --git a/security/security.c b/security/security.c
> index d7b15ea67c3f..8e5379a76369 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -5350,6 +5350,27 @@ int security_audit_rule_match(u32 secid, u32 field, u32 op, void *lsmrule)
>  }
>  #endif /* CONFIG_AUDIT */
>  
> +#ifdef CONFIG_IMA_LSM_RULES
> +/*
> + * The integrity subsystem uses the same hooks as
> + * the audit subsystem.
> + */
> +int ima_filter_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule)
> +{
> +	return call_int_hook(audit_rule_init, 0, field, op, rulestr, lsmrule);
> +}
> +
> +void ima_filter_rule_free(void *lsmrule)
> +{
> +	call_void_hook(audit_rule_free, lsmrule);
> +}
> +
> +int ima_filter_rule_match(u32 secid, u32 field, u32 op, void *lsmrule)
> +{
> +	return call_int_hook(audit_rule_match, 0, secid, field, op, lsmrule);
> +}
> +#endif /* CONFIG_IMA_LSM_RULES */
> +
>  #ifdef CONFIG_BPF_SYSCALL
>  /**
>   * security_bpf() - Check if the bpf syscall operation is allowed