[PATCH] binder: make sure fd closes complete

[Dan Carpenter]

On Thu, Sep 02, 2021 at 08:35:35AM -0700, Todd Kjos wrote:
> On Tue, Aug 31, 2021 at 12:24 AM Martijn Coenen <maco at android.com> wrote:
> >
> > On Mon, Aug 30, 2021 at 9:51 PM 'Todd Kjos' via kernel-team
> > <kernel-team at 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 at google.com>
> > Reviewed-by: Martijn Coenen <maco at android.com>
> 
> Please also add to stable releases 5.4 and later.

It would be better if this had a fixes tag so we knew which is the first
buggy commit.

There was a long Project Zero article about the Bad Binder exploit
because commit f5cb779ba163 ("ANDROID: binder: remove waitqueue when
thread exits.") was marked as # 4.14 but it didn't have a Fixes tag and
the actual buggy commit was in 4.9.

regards,
dan carpenter