linux-kernel - Re: [4.4, 027/193] binder: check for binder_thread allocation failure in binder

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Date:   Mon, 26 Feb 2018 11:05:59 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot <syzkaller@...glegroups.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [4.4, 027/193] binder: check for binder_thread allocation
 failure in binder_poll()

On Mon, Feb 26, 2018 at 10:57:54AM -0800, Eric Biggers wrote:
> Hi Guenter,
> 
> On Mon, Feb 26, 2018 at 09:21:19AM -0800, Guenter Roeck wrote:
> > On Fri, Feb 23, 2018 at 07:24:20PM +0100, gregkh@...uxfoundation.org wrote:
> > > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > > 
> > > ------------------
> > > 
> > > From: Eric Biggers <ebiggers@...gle.com>
> > > 
> > > commit f88982679f54f75daa5b8eff3da72508f1e7422f upstream.
> > > 
> > > If the kzalloc() in binder_get_thread() fails, binder_poll()
> > > dereferences the resulting NULL pointer.
> > > 
> > > Fix it by returning POLLERR if the memory allocation failed.
> > > 
> > > This bug was found by syzkaller using fault injection.
> > > 
> > > Reported-by: syzbot <syzkaller@...glegroups.com>
> > > Fixes: 457b9a6f09f0 ("Staging: android: add binder driver")
> > > Cc: stable@...r.kernel.org
> > > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > ---
> > >  drivers/android/binder.c |    2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > --- a/drivers/android/binder.c
> > > +++ b/drivers/android/binder.c
> > > @@ -2622,6 +2622,8 @@ static unsigned int binder_poll(struct f
> > >  	binder_lock(__func__);
> > >  
> > >  	thread = binder_get_thread(proc);
> > > +	if (!thread)
> > > +		return POLLERR;
> > >  
> > Noticed while merging into chromeos-4.4:
> > 
> > This will cause trouble in v4.4.y. Notice the call to "binder_lock(__func__)"
> > above. This call has been removed upstream, but not in v4.4.y. As a result,
> > the lock won't be released, which will result in subsequent hangups
> > if/when the function is called again.
> > 
> > v4.9.y has the same problem. v4.14.y+ are fine.
> > 
> > Greg - can you fix this up yourself or do you want me to send fixup
> > patches ? It might take a few days for me to get to it.
> > 
> > Guenter
> 
> Thanks for spotting this!  I'll send a patch to fix it.
> 
Thanks!

Guenter