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From:   Kees Cook <keescook@chromium.org>
Date:   Tue, 30 Oct 2018 14:52:43 -0700
Message-ID: <CAGXu5j+tRWseaecob04U5iXHa-P_z=Hvj3PmhE5YWFUO=LT7Sw@mail.gmail.com>
Subject: Re: [PATCH v4] pstore: Avoid duplicate call of persistent_ram_zap()
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     Peng Wang <wangpeng15@xiaomi.com>,
        Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        LKML <linux-kernel@vger.kernel.org>, vipwangerxiao@gmail.com
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On Tue, Oct 30, 2018 at 2:38 PM, Joel Fernandes <joel@joelfernandes.org> wrote:
> On Tue, Oct 30, 2018 at 03:52:34PM +0800, Peng Wang wrote:
>> When initialing prz with invalid data in buffer(no PERSISTENT_RAM_SIG),
>> function call path is like this:
>>
>> ramoops_init_prz ->
>> |
>> |-> persistent_ram_new -> persistent_ram_post_init -> persistent_ram_zap
>> |
>> |-> persistent_ram_zap
>>
>> As we can see, persistent_ram_zap() is called twice.
>> We can avoid this by adding an option to persistent_ram_new(), and
>> only call persistent_ram_zap() when it is needed.
>>
>> Signed-off-by: Peng Wang <wangpeng15@xiaomi.com>
>> ---
>>  fs/pstore/ram.c            | 4 +---
>>  fs/pstore/ram_core.c       | 5 +++--
>>  include/linux/pstore_ram.h | 1 +
>>  3 files changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
>> index ffcff6516e89..b51901f97dc2 100644
>> --- a/fs/pstore/ram.c
>> +++ b/fs/pstore/ram.c
>> @@ -640,7 +640,7 @@ static int ramoops_init_prz(const char *name,
>>
>>       label = kasprintf(GFP_KERNEL, "ramoops:%s", name);
>>       *prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info,
>> -                               cxt->memtype, 0, label);
>> +                               cxt->memtype, PRZ_FLAG_ZAP_OLD, label);
>>       if (IS_ERR(*prz)) {
>>               int err = PTR_ERR(*prz);
>
> Looks good to me except the minor comment below:
>
>>
>> @@ -649,8 +649,6 @@ static int ramoops_init_prz(const char *name,
>>               return err;
>>       }
>>
>> -     persistent_ram_zap(*prz);
>> -
>>       *paddr += sz;
>>
>>       return 0;
>> diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
>> index 12e21f789194..2ededd1ea1c2 100644
>> --- a/fs/pstore/ram_core.c
>> +++ b/fs/pstore/ram_core.c
>> @@ -505,15 +505,16 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
>>                       pr_debug("found existing buffer, size %zu, start %zu\n",
>>                                buffer_size(prz), buffer_start(prz));
>>                       persistent_ram_save_old(prz);
>> -                     return 0;
>> +                     if (!(prz->flags & PRZ_FLAG_ZAP_OLD))
>> +                             return 0;
>
> This could be written differently.
>
> We could just do:
>
> if (prz->flags & PRZ_FLAG_ZAP_OLD)
>         persistent_ram_zap(prz);
>
> And remove the zap from below below.

I actually rearranged things a little to avoid additional round-trips
on the mailing list. :)

> Since Kees already took this patch, I can just patch this in my series if
> Kees and you are Ok with this suggestion.

I've put it up here:
https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=pstore/devel&id=ac564e023248e3f4d87917b91d12376ddfca5000

> Sorry for the delay in my RFC series, I just got back from paternity leave
> and I'm catching up with email.

No worries! It's many weeks until the next merge window. :)

-- 
Kees Cook