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From: Kees Cook <keescook@chromium.org>
Date: Tue, 7 Mar 2017 08:18:40 -0800
Message-ID: <CAGXu5jLWBFVH92PK+vPAsv5sDyLCX6=85NWFXNetC0JDBNUUqQ@mail.gmail.com>
Subject: Re: [PATCH 03/18] pstore: Avoid race in module unloading
To: Namhyung Kim <namhyung@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Nobuhiro Iwamatsu <nobuhiro.iwamatsu.kw@hitachi.com>,
        Qiuxu Zhuo <qiuxu.zhuo@intel.com>,
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        Anton Vorontsov <anton@enomsg.org>, Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
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        Matt Fleming <matt@codeblueprint.co.uk>,
        Nathan Fontenot <nfont@linux.vnet.ibm.com>,
        Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>,
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        Paul Gortmaker <paul.gortmaker@windriver.com>,
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On Tue, Mar 7, 2017 at 8:16 AM, Namhyung Kim <namhyung@gmail.com> wrote:
> 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?

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@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
>>


-- 
Kees Cook
Pixel Security