linux-kernel - Re: [PATCH] ANDROID: binder: remove waitqueue when thread exits.

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Message-ID: <20180105122021.GF19551@kroah.com>
Date:   Fri, 5 Jan 2018 13:20:21 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Martijn Coenen <maco@...roid.com>
Cc:     john.stultz@...aro.org, tkjos@...gle.com, arve@...roid.com,
        linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
        maco@...gle.com, ebiggers@...gle.com
Subject: Re: [PATCH] ANDROID: binder: remove waitqueue when thread exits.

On Fri, Jan 05, 2018 at 11:27:07AM +0100, Martijn Coenen wrote:
> binder_poll() passes the thread->wait waitqueue that
> can be slept on for work. When a thread that uses
> epoll explicitly exits using BINDER_THREAD_EXIT,
> the waitqueue is freed, but it is never removed
> from the corresponding epoll data structure. When
> the process subsequently exits, the epoll cleanup
> code tries to access the waitlist, which results in
> a use-after-free.
> 
> Prevent this by using POLLFREE when the thread exits.
> 
> Signed-off-by: Martijn Coenen <maco@...roid.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> ---
>  drivers/android/binder.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)

Should this be a 4.15-final thing, as well as backported to any range of
older kernels?

thanks,

greg k-h