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audit: acquire creds selectively to reduce atomic op overhead 

Commit c69e8d9c01 ("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>
This commit is contained in:
Tony Jones 2011-04-27 15:10:49 +02:00 committed by Jiri Kosina
parent 80e8ff562a
commit f562988350
1 changed files with 17 additions and 10 deletions
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27
kernel/auditsc.c
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@ -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;
@ -637,10 +645,8 @@ static int audit_filter_rules(struct task_struct *tsk,
break;
}
if (!result) {
put_cred(cred);
if (!result)
return 0;
}
}
if (ctx) {
@ -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;