linux-kernel - Re: [PATCH] Android / binder: Fix broken walk in binder_node

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Date:	Fri, 21 Feb 2014 12:30:32 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	"Compostella, Jeremy" <jeremy.compostella@...il.com>
Cc:	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	"Gross, Mark" <mark.gross@...el.com>,
	"Ernst, Eric" <eric.ernst@...el.com>, Arve <arve@...roid.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Mirsal Ennaime <mirsal@...sal.fr>
Subject: Re: [PATCH] Android / binder: Fix broken walk in
 binder_node_release()

On Thu, Feb 20, 2014 at 02:22:53PM +0100, Compostella, Jeremy wrote:
> From: "Compostella, Jeremy" <jeremy.compostella@...el.com>
> 
> This bug can manifest itself in several situations, here is the one that made me
> hunt it last week:
> 
> When an Android device is encrypted, Android starts all the init services of
> core and main levels, then it asks for the password and checks it trying to
> mount /data.  On success, it kills all the main services, mount /data and
> restart all the main services.
> 
> Unfortunately, on restart of those main services we observe :
> 
> DisplayManager       Could not get display information from display manager.
> DisplayManager       android.os.DeadObjectException
> DisplayManager       at android.os.BinderProxy.transact(Native Method)
> DisplayManager       at android.hardware.display.IDisplayManager$Stub$Proxy.getDisplayInfo(IDisplayManager.java:228)
> DisplayManager       at android.hardware.display.DisplayManagerGlobal.getDisplayInfo(DisplayManagerGlobal.java:117)
> DisplayManager       at android.hardware.display.DisplayManagerGlobal.getCompatibleDisplay(DisplayManagerGlobal.java:176)
> DisplayManager       at android.app.ResourcesManager.getDisplayMetricsLocked(ResourcesManager.java:96)
> DisplayManager       at android.app.ResourcesManager.getDisplayMetricsLocked(ResourcesManager.java:74)
> [...]
> 
> Which means that the 'display' service is registered into the service_manager
> but point to a dead object (understand died process).  This error is the first
> one of a chain of missing "remote" objects causing the death of processes until
> the system can recovery by itself a few seconds later.
> 
> The binder driver allows a "process" to ask a notification when a particular
> reference die.  In that case, the binder driver associate a death object to this
> reference.
> 
> When the system_server process died, the file descriptor to the binder driver is
> automatically released and the binder driver will walk all the references
> associated to this process to unallocate them.  When such a reference has a
> death object associated it will execute a task to notify the death to the
> previously register process usually the service_manager process.
> 
> The bug is that this walk on all the references is broken due to an
> unfornate refactoring made by the following patch :
> 
>         commit 008fa749e0fe5b2fffd20b7fe4891bb80d072c6a
>         Author: Mirsal Ennaime <mirsal@...sal.fr>
>         Date:   Tue Mar 12 11:41:59 2013 +0100
> 
> which break the loop if the current reference does not have a death object
> instead of continuing to the next reference.  As a consequence all the next
> references will not be correctly unallocate and no death notification will be
> sent for them.
> 
> Signed-off-by: Jeremy Compostella <jeremy.compostella@...el.com>
> ---
>  drivers/staging/android/binder.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)

Thanks, but this fix has already been submitted, and has been part of
the Android kernel git tree for a while with the authorship of someone
else, so I'll use that patch instead when applying it.

greg k-h
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