linux-kernel - Re: [PATCH v2 2/2] binder: Gracefully handle BINDER_TYPE_FDA objects with num

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Date:   Tue, 19 Apr 2022 11:48:14 -0700
From:   Todd Kjos <tkjos@...gle.com>
To:     Alessandro Astone <ales.astone@...il.com>
Cc:     tkjos@...roid.com, gregkh@...uxfoundation.org, brauner@...nel.org,
        arve@...roid.com, linux-kernel@...r.kernel.org, maco@...roid.com,
        Joel Fernandes <joel@...lfernandes.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v2 2/2] binder: Gracefully handle BINDER_TYPE_FDA objects
 with num_fds=0

On Fri, Apr 15, 2022 at 5:00 AM Alessandro Astone <ales.astone@...il.com> wrote:
>
> Some android userspace is sending BINDER_TYPE_FDA objects with
> num_fds=0. Like the previous patch, this is reproducible when
> playing a video.
>
> Before commit 09184ae9b575 BINDER_TYPE_FDA objects with num_fds=0
> were 'correctly handled', as in no fixup was performed.
>
> After commit 09184ae9b575 we aggregate fixup and skip regions in
> binder_ptr_fixup structs and distinguish between the two by using
> the skip_size field: if it's 0, then it's a fixup, otherwise skip.
> When processing BINDER_TYPE_FDA objects with num_fds=0 we add a
> skip region of skip_size=0, and this causes issues because now
> binder_do_deferred_txn_copies will think this was a fixup region.
>
> To address that, return early from binder_translate_fd_array to
> avoid adding an empty skip region.
>
> Fixes: 09184ae9b575 ("binder: defer copies of pre-patched txn data")
> Signed-off-by: Alessandro Astone <ales.astone@...il.com>

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

> ---
>  drivers/android/binder.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 31176edb1069..f3b639e89dd8 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -2491,6 +2491,9 @@ static int binder_translate_fd_array(struct list_head *pf_head,
>         struct binder_proc *proc = thread->proc;
>         int ret;
>
> +       if (fda->num_fds == 0)
> +               return 0;
> +
>         fd_buf_size = sizeof(u32) * fda->num_fds;
>         if (fda->num_fds >= SIZE_MAX / sizeof(u32)) {
>                 binder_user_error("%d:%d got transaction with invalid number of fds (%lld)\n",
> --
> 2.35.1
>