linux-kernel - Re: [PATCH] binder: make sure fd closes complete

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Date:   Tue, 14 Sep 2021 09:01:43 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Todd Kjos <tkjos@...gle.com>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Martijn Coenen <maco@...roid.com>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        LKML <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Martijn Coenen <maco@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        kernel-team@...roid.com, Christian Brauner <christian@...uner.io>
Subject: Re: [PATCH] binder: make sure fd closes complete

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@...cle.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@...roid.com> wrote:
> > > >
> > > > On Mon, Aug 30, 2021 at 9:51 PM 'Todd Kjos' via kernel-team
> > > > <kernel-team@...roid.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@...gle.com>
> > > > Reviewed-by: Martijn Coenen <maco@...roid.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