On Fri, Sep 27, 2024 at 12:19 AM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
>
> On Fri, Sep 27, 2024 at 1:37 AM Carlos Llamas <cmllamas@xxxxxxxxxx> wrote:
> >
> > Alice points out that binder_request_freeze_notification() should not
> > return EINVAL when the relevant node is dead [1]. The node can die at
> > any point even if the user input is valid. Instead, allow the request
> > to be allocated but skip the initial notification for dead nodes. This
> > avoids propagating unnecessary errors back to userspace.
> >
> > Fixes: d579b04a52a1 ("binder: frozen notification")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Suggested-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> > Link: https://lore.kernel.org/all/CAH5fLghapZJ4PbbkC8V5A6Zay-_sgTzwVpwqk6RWWUNKKyJC_Q@xxxxxxxxxxxxxx/ [1]
> > Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
> > ---
> > drivers/android/binder.c | 28 +++++++++++++---------------
> > 1 file changed, 13 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> > index 73dc6cbc1681..415fc9759249 100644
> > --- a/drivers/android/binder.c
> > +++ b/drivers/android/binder.c
> > @@ -3856,7 +3856,6 @@ binder_request_freeze_notification(struct binder_proc *proc,
> > {
> > struct binder_ref_freeze *freeze;
> > struct binder_ref *ref;
> > - bool is_frozen;
> >
> > freeze = kzalloc(sizeof(*freeze), GFP_KERNEL);
> > if (!freeze)
> > @@ -3872,32 +3871,31 @@ binder_request_freeze_notification(struct binder_proc *proc,
> > }
> >
> > binder_node_lock(ref->node);
> > -
> > - if (ref->freeze || !ref->node->proc) {
> > - binder_user_error("%d:%d invalid BC_REQUEST_FREEZE_NOTIFICATION %s\n",
> > - proc->pid, thread->pid,
> > - ref->freeze ? "already set" : "dead node");
> > + if (ref->freeze) {
> > + binder_user_error("%d:%d BC_REQUEST_FREEZE_NOTIFICATION already set\n",
> > + proc->pid, thread->pid);
> > binder_node_unlock(ref->node);
> > binder_proc_unlock(proc);
> > kfree(freeze);
> > return -EINVAL;
> > }
> > - binder_inner_proc_lock(ref->node->proc);
> > - is_frozen = ref->node->proc->is_frozen;
> > - binder_inner_proc_unlock(ref->node->proc);
> >
> > binder_stats_created(BINDER_STAT_FREEZE);
> > INIT_LIST_HEAD(&freeze->work.entry);
> > freeze->cookie = handle_cookie->cookie;
> > freeze->work.type = BINDER_WORK_FROZEN_BINDER;
> > - freeze->is_frozen = is_frozen;
> > -
> > ref->freeze = freeze;
> >
> > - binder_inner_proc_lock(proc);
> > - binder_enqueue_work_ilocked(&ref->freeze->work, &proc->todo);
> > - binder_wakeup_proc_ilocked(proc);
> > - binder_inner_proc_unlock(proc);
> > + if (ref->node->proc) {
> > + binder_inner_proc_lock(ref->node->proc);
> > + freeze->is_frozen = ref->node->proc->is_frozen;
> > + binder_inner_proc_unlock(ref->node->proc);
> > +
> > + binder_inner_proc_lock(proc);
> > + binder_enqueue_work_ilocked(&freeze->work, &proc->todo);
> > + binder_wakeup_proc_ilocked(proc);
> > + binder_inner_proc_unlock(proc);
>
> This is not a problem with your change ... but, why exactly are we
> scheduling the BINDER_WORK_FROZEN_BINDER right after creating it? For
> death notications, we only schedule it immediately if the process is
> dead. So shouldn't we only schedule it if the process is not frozen?
>
> And if the answer is that frozen notifications are always sent
> immediately to notify about the current state, then we should also
> send one for a dead process ... maybe. I guess a dead process is not
> frozen?
Yes this is to immediately notify about the current state (frozen or
unfrozen). A dead process is in neither state so it feels more correct
not to send either?
>
> > + }
> >
> > binder_node_unlock(ref->node);
> > binder_proc_unlock(proc);
> > --
> > 2.46.1.824.gd892dcdcdd-goog
> >
