Re: [PATCH] binder: make sure fd closes complete

[Martijn Coenen <maco@android.com>]

On Mon, Aug 30, 2021 at 9:51 PM 'Todd Kjos' via kernel-team
<kernel-team@android.com> wrote:
>
> During BC_FREE_BUFFER processing, the BINDER_TYPE_FDA object
> cleanup may close 1 or more fds. The close operations are
> completed using the task work mechanism -- which means the thread
> needs to return to userspace or the file object may never be
> dereferenced -- which can lead to hung processes.
>
> Force the binder thread back to userspace if an fd is closed during
> BC_FREE_BUFFER handling.
>
> Signed-off-by: Todd Kjos <tkjos@google.com>
Reviewed-by: Martijn Coenen <maco@android.com>

> ---
>  drivers/android/binder.c | 23 +++++++++++++++++------
>  1 file changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index bcec598b89f2..c2823f0d588f 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -1852,6 +1852,7 @@ static void binder_deferred_fd_close(int fd)
>  }
>
>  static void binder_transaction_buffer_release(struct binder_proc *proc,
> +                                             struct binder_thread *thread,
>                                               struct binder_buffer *buffer,
>                                               binder_size_t failed_at,
>                                               bool is_failure)
> @@ -2011,8 +2012,16 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
>                                                 &proc->alloc, &fd, buffer,
>                                                 offset, sizeof(fd));
>                                 WARN_ON(err);
> -                               if (!err)
> +                               if (!err) {
>                                         binder_deferred_fd_close(fd);
> +                                       /*
> +                                        * Need to make sure the thread goes
> +                                        * back to userspace to complete the
> +                                        * deferred close
> +                                        */
> +                                       if (thread)
> +                                               thread->looper_need_return = true;
> +                               }
>                         }
>                 } break;
>                 default:
> @@ -3105,7 +3114,7 @@ static void binder_transaction(struct binder_proc *proc,
>  err_copy_data_failed:
>         binder_free_txn_fixups(t);
>         trace_binder_transaction_failed_buffer_release(t->buffer);
> -       binder_transaction_buffer_release(target_proc, t->buffer,
> +       binder_transaction_buffer_release(target_proc, NULL, t->buffer,
>                                           buffer_offset, true);
>         if (target_node)
>                 binder_dec_node_tmpref(target_node);
> @@ -3184,7 +3193,9 @@ static void binder_transaction(struct binder_proc *proc,
>   * Cleanup buffer and free it.
>   */
>  static void
> -binder_free_buf(struct binder_proc *proc, struct binder_buffer *buffer)
> +binder_free_buf(struct binder_proc *proc,
> +               struct binder_thread *thread,
> +               struct binder_buffer *buffer)
>  {
>         binder_inner_proc_lock(proc);
>         if (buffer->transaction) {
> @@ -3212,7 +3223,7 @@ binder_free_buf(struct binder_proc *proc, struct binder_buffer *buffer)
>                 binder_node_inner_unlock(buf_node);
>         }
>         trace_binder_transaction_buffer_release(buffer);
> -       binder_transaction_buffer_release(proc, buffer, 0, false);
> +       binder_transaction_buffer_release(proc, thread, buffer, 0, false);
>         binder_alloc_free_buf(&proc->alloc, buffer);
>  }
>
> @@ -3414,7 +3425,7 @@ static int binder_thread_write(struct binder_proc *proc,
>                                      proc->pid, thread->pid, (u64)data_ptr,
>                                      buffer->debug_id,
>                                      buffer->transaction ? "active" : "finished");
> -                       binder_free_buf(proc, buffer);
> +                       binder_free_buf(proc, thread, buffer);
>                         break;
>                 }
>
> @@ -4107,7 +4118,7 @@ static int binder_thread_read(struct binder_proc *proc,
>                         buffer->transaction = NULL;
>                         binder_cleanup_transaction(t, "fd fixups failed",
>                                                    BR_FAILED_REPLY);
> -                       binder_free_buf(proc, buffer);
> +                       binder_free_buf(proc, thread, buffer);
>                         binder_debug(BINDER_DEBUG_FAILED_TRANSACTION,
>                                      "%d:%d %stransaction %d fd fixups failed %d/%d, line %d\n",
>                                      proc->pid, thread->pid,
> --
> 2.33.0.259.gc128427fd7-goog
>
>