[PATCH] binder: make sure fd closes complete

Todd Kjos tkjos at google.com
Fri Sep 3 19:38:26 UTC 2021


On Fri, Sep 3, 2021 at 1:06 AM Dan Carpenter <dan.carpenter at 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 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.

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?

>
> regards,
> dan carpenter
>
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