linux-kernel - Re: [PATCH v4] pstore: Avoid duplicate call of persistent_ram

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Date:   Tue, 30 Oct 2018 14:21:59 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peng Wang <wangpeng15@...omi.com>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        LKML <linux-kernel@...r.kernel.org>, vipwangerxiao@...il.com
Subject: Re: [PATCH v4] pstore: Avoid duplicate call of persistent_ram_zap()

On Tue, Oct 30, 2018 at 12:52 AM, Peng Wang <wangpeng15@...omi.com> 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@...omi.com>

Thanks! I've applied this to my devel branch. I'll have it in
linux-next once -rc2 lands.

-Kees

> ---
>  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);
>
> @@ -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;
>                 }
>         } else {
>                 pr_debug("no valid data in buffer (sig = 0x%08x)\n",
>                          prz->buffer->sig);
> +               prz->buffer->sig = sig;
>         }
>
>         /* Rewind missing or invalid memory area. */
> -       prz->buffer->sig = sig;
>         persistent_ram_zap(prz);
>
>         return 0;
> diff --git a/include/linux/pstore_ram.h b/include/linux/pstore_ram.h
> index 602d64725222..6e94980357d2 100644
> --- a/include/linux/pstore_ram.h
> +++ b/include/linux/pstore_ram.h
> @@ -30,6 +30,7 @@
>   * PRZ_FLAG_NO_LOCK is used. For all other cases, locking is required.
>   */
>  #define PRZ_FLAG_NO_LOCK       BIT(0)
> +#define PRZ_FLAG_ZAP_OLD       BIT(1)
>
>  struct persistent_ram_buffer;
>  struct rs_control;
> --
> 2.19.1
>



-- 
Kees Cook