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SubjectRe: [PATCH 3/3] auditsc: Do not use RCU primitive to read from cred pointer
On Tue, Feb 11, 2020 at 10:19:04AM -0500, Paul Moore wrote:
> On Fri, Feb 7, 2020 at 1:08 PM Amol Grover <frextrite@gmail.com> wrote:
> >
> > task_struct::cred is only used task-synchronously and does
> > not require any RCU locks, hence, rcu_dereference_check is
> > not required to read from it.
> >
> > Suggested-by: Jann Horn <jannh@google.com>
> > Co-developed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > Signed-off-by: Amol Grover <frextrite@gmail.com>
> > ---
> > kernel/auditsc.c | 15 +++++----------
> > 1 file changed, 5 insertions(+), 10 deletions(-)
>
> Considering the other changes in this patchset this change seems
> reasonable to me. I'm assuming you were intending this patchset to go
> in via some tree other than audit?
>

Yes, that's correct. Thank you for the ack!

> Acked-by: Paul Moore <paul@paul-moore.com>
>
> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index 4effe01ebbe2..d3510513cdd1 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> > @@ -430,24 +430,19 @@ static int audit_field_compare(struct task_struct *tsk,
> > /* 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.
> > - *
> > - * 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,
> > - bool task_creation)
> > + enum audit_state *state)
> > {
> > const struct cred *cred;
> > int i, need_sid = 1;
> > u32 sid;
> > unsigned int sessionid;
> >
> > - cred = rcu_dereference_check(tsk->cred, tsk == current || task_creation);
> > + cred = tsk->cred;
> >
> > for (i = 0; i < rule->field_count; i++) {
> > struct audit_field *f = &rule->fields[i];
> > @@ -745,7 +740,7 @@ 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, true)) {
> > + &state)) {
> > if (state == AUDIT_RECORD_CONTEXT)
> > *key = kstrdup(e->rule.filterkey, GFP_ATOMIC);
> > rcu_read_unlock();
> > @@ -791,7 +786,7 @@ static enum audit_state audit_filter_syscall(struct task_struct *tsk,
> > list_for_each_entry_rcu(e, list, list) {
> > if (audit_in_mask(&e->rule, ctx->major) &&
> > audit_filter_rules(tsk, &e->rule, ctx, NULL,
> > - &state, false)) {
> > + &state)) {
> > rcu_read_unlock();
> > ctx->current_state = state;
> > return state;
> > @@ -815,7 +810,7 @@ static int audit_filter_inode_name(struct task_struct *tsk,
> >
> > list_for_each_entry_rcu(e, list, list) {
> > if (audit_in_mask(&e->rule, ctx->major) &&
> > - audit_filter_rules(tsk, &e->rule, ctx, n, &state, false)) {
> > + audit_filter_rules(tsk, &e->rule, ctx, n, &state)) {
> > ctx->current_state = state;
> > return 1;
> > }
> > --
> > 2.24.1
> >
>
>
> --
> paul moore
> www.paul-moore.com

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