linux-kernel - Re: [PATCH 03/18] pstore: Avoid race in module unloading

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Message-ID: <CADWwUUZAxwUqHU9eRrtP5Hk7KO9KkyvdBy7Z5Xehwhv43fvZVQ@mail.gmail.com>
Date:   Wed, 8 Mar 2017 01:16:43 +0900
From:   Namhyung Kim <namhyung@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Nobuhiro Iwamatsu <nobuhiro.iwamatsu.kw@...achi.com>,
        Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
        Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
        Daniel Axtens <dja@...ens.net>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Geliang Tang <geliangtang@....com>,
        linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
        linux-efi@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH 03/18] pstore: Avoid race in module unloading

Hi Kees,

On Tue, Mar 7, 2017 at 6:55 AM, Kees Cook <keescook@...omium.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@...omium.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
>