linux-kernel - Re: [PATCH] pstore/ram: Fix console ramoops to show the previous boot logs

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Date:   Thu, 17 Jan 2019 09:11:21 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Guenter Roeck <groeck@...omium.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Doug Anderson <dianders@...omium.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] pstore/ram: Fix console ramoops to show the previous boot logs

On Wed, Jan 16, 2019 at 10:27 PM Sai Prakash Ranjan
<saiprakash.ranjan@...eaurora.org> wrote:
>
> commit b05c950698fe ("pstore/ram: Simplify ramoops_get_next_prz()
> arguments") changed update assignment in getting next persistent
> ram zone by adding a check for record type. But the check always
> returns true since the record type is assigned 0. And this breaks
> console ramoops by showing current console log instead of previous
> log on warm reset and hard reset (actually hard reset should not
> be showing any logs).
>
> Fix this by having persistent ram zone type check instead of record
> type check. Tested this on SDM845 MTP and dragonboard 410c.
>
> Reproducing this issue is simple as below:
>
> 1. Trigger hard reset and mount pstore. Will see console-ramoops
>    record in the mounted location which is the current log.
>
> 2. Trigger warm reset and mount pstore. Will see the current
>    console-ramoops record instead of previous record.
>
> Fixes: b05c950698fe ("pstore/ram: Simplify ramoops_get_next_prz() arguments")
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>

Whoops! Thanks for catching this! I've adjusted the patch slightly (no
need for a local variable), and will send this to Linus.

-Kees

>
> ---
>
> I guess commit msg can be improved.
> ---
>  fs/pstore/ram.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index 96f7d32cd184..441a44215456 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -128,7 +128,7 @@ ramoops_get_next_prz(struct persistent_ram_zone *przs[], int id,
>                      struct pstore_record *record)
>  {
>         struct persistent_ram_zone *prz;
> -       bool update = (record->type == PSTORE_TYPE_DMESG);
> +       bool update;
>
>         /* Give up if we never existed or have hit the end. */
>         if (!przs)
> @@ -138,6 +138,8 @@ ramoops_get_next_prz(struct persistent_ram_zone *przs[], int id,
>         if (!prz)
>                 return NULL;
>
> +       update = (prz->type == PSTORE_TYPE_DMESG);
> +
>         /* Update old/shadowed buffer. */
>         if (update)
>                 persistent_ram_save_old(prz);
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> of Code Aurora Forum, hosted by The Linux Foundation
>


-- 
Kees Cook