Re: [PATCH] binder: Remove bogus warning on failed same-process transaction

From: Todd Kjos <tkjos@google.com>
To: Jann Horn <jannh@google.com>
Cc: "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Arve Hjønnevåg" <arve@android.com>,
	"Todd Kjos" <tkjos@android.com>,
	"Martijn Coenen" <maco@android.com>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	"Christian Brauner" <christian@brauner.io>,
	"Hridya Valsaraju" <hridya@google.com>,
	"Suren Baghdasaryan" <surenb@google.com>,
	"open list:ANDROID DRIVERS" <devel@driverdev.osuosl.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] binder: Remove bogus warning on failed same-process transaction
Date: Thu, 6 Aug 2020 09:58:23 -0700	[thread overview]
Message-ID: <CAHRSSEwgfaQhqgHhfKWKpd78WAT20aj49exUgbJqhVXp7NBY_w@mail.gmail.com> (raw)
In-Reply-To: <20200806165359.2381483-1-jannh@google.com>

On Thu, Aug 6, 2020 at 9:54 AM Jann Horn <jannh@google.com> wrote:
>
> While binder transactions with the same binder_proc as sender and recipient
> are forbidden, transactions with the same task_struct as sender and
> recipient are possible (even though currently there is a weird check in
> binder_transaction() that rejects them in the target==0 case).
> Therefore, task_struct identities can't be used to distinguish whether
> the caller is running in the context of the sender or the recipient.
>
> Since I see no easy way to make this WARN_ON() useful and correct, let's
> just remove it.
>
> Fixes: 44d8047f1d87 ("binder: use standard functions to allocate fds")
> Reported-by: syzbot+e113a0b970b7b3f394ba@syzkaller.appspotmail.com
> Signed-off-by: Jann Horn <jannh@google.com>

Acked-by: Todd Kjos <tkjos@google.com>

> ---
>  drivers/android/binder.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index f936530a19b0..5b0376344dbe 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -2344,8 +2344,6 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
>                          * file is done when the transaction is torn
>                          * down.
>                          */
> -                       WARN_ON(failed_at &&
> -                               proc->tsk == current->group_leader);
>                 } break;
>                 case BINDER_TYPE_PTR:
>                         /*
>
> base-commit: 47ec5303d73ea344e84f46660fff693c57641386
> --
> 2.28.0.163.g6104cc2f0b6-goog
>