Re: [PATCH v2] audit: add fields to exclude filter by reusing user filter

[Paul Moore]

On Tue, Jun 14, 2016 at 5:04 PM, Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> RFE: add additional fields for use in audit filter exclude rules
> https://github.com/linux-audit/audit-kernel/issues/5
>
> Re-factor and combine audit_filter_type() with audit_filter_user() to
> use audit_filter_user_rules() to enable the exclude filter to
> additionally filter on PID, UID, GID, AUID, LOGINUID_SET, SUBJ_*.
>
> The process of combining the similar audit_filter_user() and
> audit_filter_type() functions, required inverting the meaning and
> including the ALWAYS action of the latter.
>
> Keep the check to quit early if the list is empty.
>
> Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> ---
> v2: combine audit_filter_user() and audit_filter_type() into
> audit_filter().
> ---
>
>  include/linux/audit.h |    2 --
>  kernel/audit.c        |    4 ++--
>  kernel/audit.h        |    2 ++
>  kernel/auditfilter.c  |   46 ++++++++++------------------------------------
>  4 files changed, 14 insertions(+), 40 deletions(-)

Patches that remove more code than the add always make me happy :)

Comment below ...

> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index 32cdafb..539c1d9 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -160,8 +160,6 @@ extern void audit_log_task_info(struct audit_buffer *ab,
>  extern int                 audit_update_lsm_rules(void);
>
>                                 /* Private API (for audit.c only) */
> -extern int audit_filter_user(int type);
> -extern int audit_filter_type(int type);
>  extern int audit_rule_change(int type, __u32 portid, int seq,
>                                 void *data, size_t datasz);
>  extern int audit_list_rules_send(struct sk_buff *request_skb, int seq);
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 384374a..2dfaa19 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -914,7 +914,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
>                 if (!audit_enabled && msg_type != AUDIT_USER_AVC)
>                         return 0;
>
> -               err = audit_filter_user(msg_type);
> +               err = audit_filter(msg_type, AUDIT_FILTER_USER);
>                 if (err == 1) { /* match or error */
>                         err = 0;
>                         if (msg_type == AUDIT_USER_TTY) {
> @@ -1362,7 +1362,7 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
>         if (audit_initialized != AUDIT_INITIALIZED)
>                 return NULL;
>
> -       if (unlikely(audit_filter_type(type)))
> +       if (unlikely(!audit_filter(type, AUDIT_FILTER_TYPE)))
>                 return NULL;
>
>         if (gfp_mask & __GFP_DIRECT_RECLAIM) {
> diff --git a/kernel/audit.h b/kernel/audit.h
> index cbbe6bb..1879f02 100644
> --- a/kernel/audit.h
> +++ b/kernel/audit.h
> @@ -327,6 +327,8 @@ extern pid_t audit_sig_pid;
>  extern kuid_t audit_sig_uid;
>  extern u32 audit_sig_sid;
>
> +extern int audit_filter(int msgtype, unsigned int listtype);
> +
>  #ifdef CONFIG_AUDITSYSCALL
>  extern int __audit_signal_info(int sig, struct task_struct *t);
>  static inline int audit_signal_info(int sig, struct task_struct *t)
> diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> index 96c9a1b..f90c042 100644
> --- a/kernel/auditfilter.c
> +++ b/kernel/auditfilter.c
> @@ -1349,50 +1349,24 @@ static int audit_filter_user_rules(struct audit_krule *rule, int type,
>         return 1;
>  }
>
> -int audit_filter_user(int type)
> +int audit_filter(int msgtype, unsigned int listtype)
>  {
>         enum audit_state state = AUDIT_DISABLED;
>         struct audit_entry *e;
> -       int rc, ret;
> -
> -       ret = 1; /* Audit by default */
> +       int rc, result = 1; /* Audit by default */
>
>         rcu_read_lock();
> -       list_for_each_entry_rcu(e, &audit_filter_list[AUDIT_FILTER_USER], list) {
> -               rc = audit_filter_user_rules(&e->rule, type, &state);
> -               if (rc) {
> -                       if (rc > 0 && state == AUDIT_DISABLED)
> -                               ret = 0;
> -                       break;
> -               }
> -       }
> -       rcu_read_unlock();
> -
> -       return ret;
> -}
> -
> -int audit_filter_type(int type)
> -{
> -       struct audit_entry *e;
> -       int result = 0;
> -
> -       rcu_read_lock();
> -       if (list_empty(&audit_filter_list[AUDIT_FILTER_TYPE]))
> +       if (list_empty(&audit_filter_list[listtype]))
>                 goto unlock_and_return;
>
> -       list_for_each_entry_rcu(e, &audit_filter_list[AUDIT_FILTER_TYPE],
> -                               list) {
> -               int i;
> -               for (i = 0; i < e->rule.field_count; i++) {
> -                       struct audit_field *f = &e->rule.fields[i];
> -                       if (f->type == AUDIT_MSGTYPE) {
> -                               result = audit_comparator(type, f->op, f->val);
> -                               if (!result)
> -                                       break;
> -                       }
> +       list_for_each_entry_rcu(e, &audit_filter_list[listtype], list) {
> +               rc = audit_filter_user_rules(&e->rule, msgtype, &state);

Any reason not to do away with audit_filter_user_rules() and just
insert the code here?  As far as I can tell there are no other callers
...

> +               if (rc) {
> +                       if (rc > 0 && ((state == AUDIT_DISABLED) ||
> +                                      (listtype == AUDIT_FILTER_TYPE)))
> +                               result = 0;
> +                       break;
>                 }
> -               if (result)
> -                       goto unlock_and_return;
>         }
>  unlock_and_return:
>         rcu_read_unlock();

-- 
paul moore
www.paul-moore.com