Eric Lee / smarc-ti-linux-kernel

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Commit f562988350361bf4118dd3c3e192dff763b493d9

Authored by Tony Jones
Committed by Jiri Kosina
1 parent 80e8ff562a
Exists in master and in 20 other branches dlt-processor-sdk-linux-03.00.00.04, newt-ti-linux-3.12.y, processor-sdk-linux-01.00.00, processor-sdk-linux-02.00.01, smarc-ti-linux-3.12.10, smarc-ti-linux-3.12.y, smarc-ti-linux-3.14.y, smarc-ti-linux-3.15.y, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04, ti-linux-3.12.y, ti-linux-3.14.y, ti-linux-3.15.y, ti-lsk-linux-4.1.y

audit: acquire creds selectively to reduce atomic op overhead 

Commit c69e8d9c01db ("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: Tony Jones <tonyj@suse.de>
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Showing 1 changed file with 17 additions and 10 deletions Side-by-side Diff

... ... @@ -443,17 +443,25 @@
443 443  
444 444 /* Determine if any context name data matches a rule's watch data */
445 445 /* Compare a task_struct with an audit_rule. Return 1 on match, 0
446   - * otherwise. */
  446 + * otherwise.
  447 + *
  448 + * If task_creation is true, this is an explicit indication that we are
  449 + * filtering a task rule at task creation time. This and tsk == current are
  450 + * the only situations where tsk->cred may be accessed without an rcu read lock.
  451 + */
447 452 static int audit_filter_rules(struct task_struct *tsk,
448 453 struct audit_krule *rule,
449 454 struct audit_context *ctx,
450 455 struct audit_names *name,
451   - enum audit_state *state)
  456 + enum audit_state *state,
  457 + bool task_creation)
452 458 {
453   - const struct cred *cred = get_task_cred(tsk);
  459 + const struct cred *cred;
454 460 int i, j, need_sid = 1;
455 461 u32 sid;
456 462  
  463 + cred = rcu_dereference_check(tsk->cred, tsk == current || task_creation);
  464 +
457 465 for (i = 0; i < rule->field_count; i++) {
458 466 struct audit_field *f = &rule->fields[i];
459 467 int result = 0;
460 468  
... ... @@ -637,10 +645,8 @@
637 645 break;
638 646 }
639 647  
640   - if (!result) {
641   - put_cred(cred);
  648 + if (!result)
642 649 return 0;
643   - }
644 650 }
645 651  
646 652 if (ctx) {
... ... @@ -656,7 +662,6 @@
656 662 case AUDIT_NEVER: *state = AUDIT_DISABLED; break;
657 663 case AUDIT_ALWAYS: *state = AUDIT_RECORD_CONTEXT; break;
658 664 }
659   - put_cred(cred);
660 665 return 1;
661 666 }
662 667  
... ... @@ -671,7 +676,8 @@
671 676  
672 677 rcu_read_lock();
673 678 list_for_each_entry_rcu(e, &audit_filter_list[AUDIT_FILTER_TASK], list) {
674   - if (audit_filter_rules(tsk, &e->rule, NULL, NULL, &state)) {
  679 + if (audit_filter_rules(tsk, &e->rule, NULL, NULL,
  680 + &state, true)) {
675 681 if (state == AUDIT_RECORD_CONTEXT)
676 682 *key = kstrdup(e->rule.filterkey, GFP_ATOMIC);
677 683 rcu_read_unlock();
... ... @@ -705,7 +711,7 @@
705 711 list_for_each_entry_rcu(e, list, list) {
706 712 if ((e->rule.mask[word] & bit) == bit &&
707 713 audit_filter_rules(tsk, &e->rule, ctx, NULL,
708   - &state)) {
  714 + &state, false)) {
709 715 rcu_read_unlock();
710 716 ctx->current_state = state;
711 717 return state;
... ... @@ -743,7 +749,8 @@
743 749  
744 750 list_for_each_entry_rcu(e, list, list) {
745 751 if ((e->rule.mask[word] & bit) == bit &&
746   - audit_filter_rules(tsk, &e->rule, ctx, n, &state)) {
  752 + audit_filter_rules(tsk, &e->rule, ctx, n,
  753 + &state, false)) {
747 754 rcu_read_unlock();
748 755 ctx->current_state = state;
749 756 return;