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From: Namhyung Kim <namhyung@gmail.com>
Date: Wed, 8 Mar 2017 01:16:43 +0900
Message-ID: <CADWwUUZAxwUqHU9eRrtP5Hk7KO9KkyvdBy7Z5Xehwhv43fvZVQ@mail.gmail.com>
Subject: Re: [PATCH 03/18] pstore: Avoid race in module unloading
To: Kees Cook <keescook@chromium.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Nobuhiro Iwamatsu <nobuhiro.iwamatsu.kw@hitachi.com>,
        Qiuxu Zhuo <qiuxu.zhuo@intel.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Anton Vorontsov <anton@enomsg.org>, Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>, Len Brown <lenb@kernel.org>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Nathan Fontenot <nfont@linux.vnet.ibm.com>,
        Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>,
        Daniel Axtens <dja@axtens.net>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Geliang Tang <geliangtang@163.com>, linuxppc-dev@lists.ozlabs.org,
        linux-acpi@vger.kernel.org, linux-efi@vger.kernel.org,
        linux-doc@vger.kernel.org
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Hi Kees,

On Tue, Mar 7, 2017 at 6:55 AM, Kees Cook <keescook@chromium.org> wrote:
> Technically, it might be possible for struct pstore_info to go out of
> scope after the module_put(), so report the backend name first.

But in that case, using pstore will crash the kernel anyway, right?
If so, why pstore doesn't keep a reference until unregister?
Do I miss something?

Thanks,
Namhyung


>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  fs/pstore/platform.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index 074fe85a2078..d69ef8a840b9 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -722,10 +722,10 @@ int pstore_register(struct pstore_info *psi)
>          */
>         backend = psi->name;
>
> -       module_put(owner);
> -
>         pr_info("Registered %s as persistent store backend\n", psi->name);
>
> +       module_put(owner);
> +
>         return 0;
>  }
>  EXPORT_SYMBOL_GPL(pstore_register);
> --
> 2.7.4
>