Re: [PATCH 3/3 RESEND] auditsc: Do not use RCU primitive to read from cred pointer

[Richard Guy Briggs]

On 2020-04-03 13:26, Amol Grover wrote:
> On Thu, Apr 02, 2020 at 08:56:36AM -0400, Paul Moore wrote:
> > On Thu, Apr 2, 2020 at 1:57 AM Amol Grover <frextrite@xxxxxxxxx> 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@xxxxxxxxxx>
> > > Co-developed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Amol Grover <frextrite@xxxxxxxxx>
> > > ---
> > >  kernel/auditsc.c | 15 +++++----------
> > >  1 file changed, 5 insertions(+), 10 deletions(-)
> > 
> > This is the exact same patch I ACK'd back in February, yes?
> > 
> > https://lore.kernel.org/linux-audit/CAHC9VhQCbg1V290bYEZM+izDPRpr=XYXakohnDaMphkBBFgUaA@xxxxxxxxxxxxxx
> > 
> 
> Hi Paul,
> 
> That's correct. I've resend the series out of the fear that the first 2
> patches might've gotten lost as it's been almost a month since I last
> sent them. Could you please ack this again, and if you don't mind could
> you please go through the other 2 patches and ack them aswell?

Via who's tree are you expecting this will make it upstream?

> Thanks
> Amol
> 
> > > 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

- RGB

--
Richard Guy Briggs <rgb@xxxxxxxxxx>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635