Re: [4.4, 027/193] binder: check for binder_thread allocation failure in binder_poll()

[Eric Biggers]

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@xxxxxxxxxxxxxxxxxxx wrote:
> > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Eric Biggers <ebiggers@xxxxxxxxxx>
> > 
> > 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@xxxxxxxxxxxxxxxx>
> > Fixes: 457b9a6f09f0 ("Staging: android: add binder driver")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > ---
> >  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.

Eric