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

[Todd Kjos <tkjos@google.com>]

On Tue, Aug 31, 2021 at 12:24 AM Martijn Coenen <maco@android.com> wrote:
>
> 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>

Please also add to stable releases 5.4 and later.

>
> > ---
> >  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
> >
> >