Commit f5629883 authored by Tony Jones's avatar Tony Jones Committed by Jiri Kosina
Browse files

audit: acquire creds selectively to reduce atomic op overhead 



Commit c69e8d9c ("CRED: Use RCU to access another task's creds and to
release a task's own creds") added calls to get_task_cred and put_cred in
audit_filter_rules.  Profiling with a large number of audit rules active
on the exit chain shows that we are spending upto 48% in this routine for
syscall intensive tests, most of which is in the atomic ops.

1. The code should be accessing tsk->cred rather than tsk->real_cred.
2. Since tsk is current (or tsk is being created by copy_process) access to
tsk->cred without rcu read lock is possible.  At the request of the audit
maintainer, a new flag has been added to audit_filter_rules in order to make
this explicit and guide future code.

Signed-off-by: default avatarTony Jones <tonyj@suse.de>
Acked-by: default avatarEric Paris <eparis@redhat.com>
Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
parent 80e8ff56

kernel/auditsc.c

+17 −10
Original line number Diff line number Diff line
@@ -443,17 +443,25 @@ static int match_tree_refs(struct audit_context *ctx, struct audit_tree *tree) 


/* Determine if any context name data matches a rule's watch data */

/* Compare a task_struct with an audit_rule.  Return 1 on match, 0

 * otherwise. */

 * otherwise.

 *

 * If task_creation is true, this is an explicit indication that we are

 * filtering a task rule at task creation time.  This and tsk == current are

 * the only situations where tsk->cred may be accessed without an rcu read lock.

 */

static int audit_filter_rules(struct task_struct *tsk,

			      struct audit_krule *rule,

			      struct audit_context *ctx,

			      struct audit_names *name,

			      enum audit_state *state)

			      enum audit_state *state,

			      bool task_creation)

{

	const struct cred *cred = get_task_cred(tsk);

	const struct cred *cred;

	int i, j, need_sid = 1;

	u32 sid;



	cred = rcu_dereference_check(tsk->cred, tsk == current || task_creation);



	for (i = 0; i < rule->field_count; i++) {

		struct audit_field *f = &rule->fields[i];

		int result = 0;
@@ -637,11 +645,9 @@ static int audit_filter_rules(struct task_struct *tsk, 
			break;

		}



		if (!result) {

			put_cred(cred);

		if (!result)

			return 0;

	}

	}



	if (ctx) {

		if (rule->prio <= ctx->prio)
@@ -656,7 +662,6 @@ static int audit_filter_rules(struct task_struct *tsk, 
	case AUDIT_NEVER:    *state = AUDIT_DISABLED;	    break;

	case AUDIT_ALWAYS:   *state = AUDIT_RECORD_CONTEXT; break;

	}

	put_cred(cred);

	return 1;

}
@@ -671,7 +676,8 @@ static enum audit_state audit_filter_task(struct task_struct *tsk, char **key) 


	rcu_read_lock();

	list_for_each_entry_rcu(e, &audit_filter_list[AUDIT_FILTER_TASK], list) {

		if (audit_filter_rules(tsk, &e->rule, NULL, NULL, &state)) {

		if (audit_filter_rules(tsk, &e->rule, NULL, NULL,

				       &state, true)) {

			if (state == AUDIT_RECORD_CONTEXT)

				*key = kstrdup(e->rule.filterkey, GFP_ATOMIC);

			rcu_read_unlock();
@@ -705,7 +711,7 @@ static enum audit_state audit_filter_syscall(struct task_struct *tsk, 
		list_for_each_entry_rcu(e, list, list) {

			if ((e->rule.mask[word] & bit) == bit &&

			    audit_filter_rules(tsk, &e->rule, ctx, NULL,

					       &state)) {

					       &state, false)) {

				rcu_read_unlock();

				ctx->current_state = state;

				return state;
@@ -743,7 +749,8 @@ void audit_filter_inodes(struct task_struct *tsk, struct audit_context *ctx) 


		list_for_each_entry_rcu(e, list, list) {

			if ((e->rule.mask[word] & bit) == bit &&

			    audit_filter_rules(tsk, &e->rule, ctx, n, &state)) {

			    audit_filter_rules(tsk, &e->rule, ctx, n,

				    	       &state, false)) {

				rcu_read_unlock();

				ctx->current_state = state;

				return;

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