linux-kernel - Re: Binder regression caused by commit a43cfc87caaf

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Date:   Mon, 8 Aug 2022 22:33:27 +0200
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     Liam Howlett <liam.howlett@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Minchan Kim <minchan@...nel.org>,
        "Christian Brauner (Microsoft)" <brauner@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Martijn Coenen <maco@...roid.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Todd Kjos <tkjos@...roid.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Carlos Llamas <cmllamas@...gle.com>
Subject: Re: Binder regression caused by commit a43cfc87caaf

On Mon, Aug 8, 2022 at 9:52 PM Liam Howlett <liam.howlett@...cle.com> wrote:
> * Liam R. Howlett <Liam.Howlett@...cle.com> [220808 11:07]:
> > * Ondrej Mosnacek <omosnace@...hat.com> [220808 06:13]:
> > > Hello,
> > >
> > > FYI, since commit a43cfc87caaf ("android: binder: stop saving a
> > > pointer to the VMA") (found by git bisect) the binder test in
> > > selinux-testsuite [1] started to trigger a lockdep assert BUG() in
> > > find_vma() - see the end of [2] for an example.
> > >
> > > A minimal reproducer is:
> > > ```
> > > git clone https://github.com/SELinuxProject/selinux-testsuite.git
> > > cd selinux-testsuite/tests/binder
> > > make
> > > setenforce 0  # if SELinux is enabled
> > > ./init_binder.sh || true
> > > ./manager -n -v & sleep 2
> > > ./service_provider -n -v
> > > ```
> > > Requires the equivalent of libselinux-devel, make, gcc, and git-core
> > > Fedora packages.
> > > The last command will trigger the BUG; on good kernels it will
> > > successfully enter the ioctl loop.
> > >
> > > [1] https://github.com/SELinuxProject/selinux-testsuite/
> > > [2] https://s3.us-east-1.amazonaws.com/arr-cki-prod-datawarehouse-public/datawarehouse-public/2022/08/07/redhat:606549366/build_x86_64_redhat:606549366_x86_64/tests/5/results_0001/console.log/console.log
> > >
> >
> > Thanks.  It looks like binder has some paths that are not taking the
> > necessary mmap lock for using VMAs.  I'm looking into it now.
>
> This does not fail for me, are you sure this is the reproducer?  I see
> the manager and service_provider communicate.
>
> Looking at your trace and the code, the bug makes sense and I have
> something that will probably fix the issue, but I'd like to verify.

Hm... it seems it is necessary to have CONFIG_DEBUG_VM=y for the
particular debug check to be active. I guess you don't have that
turned on? It happens to be turned on in Fedora's release kernel, so I
didn't realize there was a specific config dependency.

Thank you for looking into it!

-- 
Ondrej Mosnacek
Senior Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.