linux-kernel - Re: [PATCH] binder: fix race that allows malicious free of live buffer

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Date:   Fri, 9 Nov 2018 08:22:44 -0800
From:   Todd Kjos <tkjos@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Todd Kjos <tkjos@...roid.com>,
        Arve Hjønnevåg <arve@...roid.com>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Martijn Coenen <maco@...gle.com>, stable@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH] binder: fix race that allows malicious free of live buffer

On Fri, Nov 9, 2018 at 4:32 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Tue, Nov 06, 2018 at 03:55:32PM -0800, Todd Kjos wrote:
> > Malicious code can attempt to free buffers using the
> > BC_FREE_BUFFER ioctl to binder. There are protections
> > against a user freeing a buffer while in use by the
> > kernel, however there was a window where BC_FREE_BUFFER
> > could be used to free a recently allocated buffer that
> > was not completely initialized. This resulted in a
> > use-after-free detected by KASAN with a malicious
> > test program.
> >
> > This window is closed by setting the buffer's
> > allow_user_free attribute to 0 when the buffer
> > is allocated or when the user has previously
> > freed it instead of waiting for the caller
> > to set it. The problem was that when the struct
> > buffer was recycled, allow_user_free was stale
> > and set to 1 allowing a free to go through.
> >
> > Signed-off-by: Todd Kjos <tkjos@...gle.com>
> > Acked-by: Arve Hjønnevåg <arve@...roid.com>
>
> No "stable" tag here?  Any idea how far back the stable backporting
> should go, if any?

Sorry about that. It should be backported to 4.14 and later.

>
> thanks,
>
> greg k-h