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

From: Greg KH <gregkh@linuxfoundation.org>
To: Todd Kjos <tkjos@google.com>
Cc: "Dan Carpenter" <dan.carpenter@oracle.com>,
	"Martijn Coenen" <maco@android.com>,
	"open list:ANDROID DRIVERS" <devel@driverdev.osuosl.org>,
	LKML <linux-kernel@vger.kernel.org>,
	stable <stable@vger.kernel.org>,
	"Arve Hjønnevåg" <arve@android.com>,
	"Martijn Coenen" <maco@google.com>,
	"Joel Fernandes" <joel@joelfernandes.org>,
	kernel-team@android.com,
	"Christian Brauner" <christian@brauner.io>
Subject: Re: [PATCH] binder: make sure fd closes complete
Date: Tue, 14 Sep 2021 09:01:43 +0200	[thread overview]
Message-ID: <YUBI1wmzXpJCH3ZS@kroah.com> (raw)
In-Reply-To: <CAHRSSEyDDmGRrc_paxJ2-Gkx=qMhKKhTr_Mpj-DiL8L1gcm5VA@mail.gmail.com>

On Fri, Sep 03, 2021 at 12:38:26PM -0700, Todd Kjos wrote:
> On Fri, Sep 3, 2021 at 1:06 AM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> >
> > 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@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.
> >
> > 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.
> 
> Good point Dan. I should have included a Fixes tag. Here is the tag
> (issue introduced in 4.20):
> 
> Fixes: 80cd795630d6 ("binder: fix use-after-free due to ksys_close()
> during fdget()")
> 
> Greg- would you like me to send a v2 with the Fixes tag and CC'ing
> stable appropriately?

I've added it to the commit when I added it to my tree, no need to
resend.

thanks,

greg k-h