linux-kernel - binderfs interferes with syzkaller?

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Date:   Sat, 25 Jan 2020 18:49:49 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Christian Brauner <christian@...uner.io>,
        Hridya Valsaraju <hridya@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: binderfs interferes with syzkaller?

Hi binder maintainers,

It seems that something has happened and now syzbot has 0 coverage in
drivers/android/binder.c:
https://storage.googleapis.com/syzkaller/cover/ci-upstream-kasan-gce-root.html
It covered at least something there before as it found some bugs in binder code.
I _suspect_ it may be related to introduction binderfs, but it's
purely based on the fact that binderfs changed lots of things there.
And I see it claims to be backward compatible.

syzkaller strategy to reach binder devices is to use
CONFIG_ANDROID_BINDER_DEVICES to create a bunch of binderN devices (to
give each test process a private one):
https://github.com/google/syzkaller/blob/master/dashboard/config/upstream-kasan.config#L5671

Then it knows how to open these /dev/binderN devices:
https://github.com/google/syzkaller/blob/master/sys/linux/dev_binder.txt#L22
and do stuff with them.

Did these devices disappear or something?