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

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Message-ID: <CAGXu5jLWBFVH92PK+vPAsv5sDyLCX6=85NWFXNetC0JDBNUUqQ@mail.gmail.com>
Date:   Tue, 7 Mar 2017 08:18:40 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Namhyung Kim <namhyung@...il.com>
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" <linuxppc-dev@...ts.ozlabs.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 03/18] pstore: Avoid race in module unloading

On Tue, Mar 7, 2017 at 8:16 AM, Namhyung Kim <namhyung@...il.com> wrote:
> 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?

I could be wrong with this, since the backend can't call unregister
until register has finished... I'll drop this patch.

-Kees

>
> 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
>>



-- 
Kees Cook
Pixel Security