On Thu, 2011-03-17 at 11:11 -0700, Tony Jones wrote: > On Tue, Mar 15, 2011 at 08:11:17PM +0000, David Howells wrote: > > Eric Paris <[email protected]> wrote: > > > > > WARN_ON(cred != current->cred && cred->refcnt != 1) > > > > 'tsk->parent == current' perhaps? Or audit_alloc() could pass a flag > > indicating the state, or just look to see if tsk->audit_context is still > > NULL. > > > > David > > Round 3. tsk->parent == current isn't an option as it's not set by > copy_process until after audit_alloc. I used a flag to provide an explicit > indication. I didn't have audit_alloc pass the flag into audit_filter_task > as there is already a explicit "process creation time" comment for this static > function. If you want it pushed all the way upto audit_alloc, let me know and > I'll revise. > > Oddly sparse didn't throw any warnings about the direct use of tsk->cred. > > tony > --- > > Commit c69e8d9c01db 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 <[email protected]>
Acked-by: Eric Paris <[email protected]> > --- > kernel/auditsc.c | 27 +++++++++++++++++---------- > 1 files changed, 17 insertions(+), 10 deletions(-) > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c > index f49a031..281dcf1 100644 > --- a/kernel/auditsc.c > +++ b/kernel/auditsc.c > @@ -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; -- Linux-audit mailing list [email protected] https://www.redhat.com/mailman/listinfo/linux-audit
