linux-kernel - Re: [PATCH] ramoops: add pdata NULL check to ramoops

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Date:   Tue, 15 Nov 2016 16:31:36 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Geliang Tang <geliangtang@...il.com>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ramoops: add pdata NULL check to ramoops_probe

On Thu, Sep 29, 2016 at 3:05 AM, Geliang Tang <geliangtang@...il.com> wrote:
> On Wed, Sep 28, 2016 at 12:45:13PM -0700, Kees Cook wrote:
>> On Wed, Sep 28, 2016 at 3:32 AM, Geliang Tang <geliangtang@...il.com> wrote:
>> > When the pdata is NULL, ramoops_probe() segfaults. So this patch adds
>> > a NULL check to it.
>>
>> While I don't mind the check, is this even possible? A device
>> triggering a ramoops probe should already have a platform_data
>> (excepting the DT case which is already covered). Is there a situation
>> you can create to trigger this Oops?
>>
>
> Hi Kees,
>
> This did happen on my device recently.
>
> We use platform_device_register() or platform_device_register_data() to set the
> ramoops_platform_data into dev->platform_data. If this ramoops_platform_data did
> not set successfully or if we pass a NULL parameter to platform_device_register(),
> we will get a NULL pdata in ramoops_probe(). This will trigger a kernel Oops.
>
> Here is a test for this. If we set dummy_data to NULL in ramoops_register_dummy(),
> we will get the Oops:
>
> @@ -747,6 +755,7 @@ static void ramoops_register_dummy(void)
>         */
>         dummy_data->ecc_info.ecc_size = ramoops_ecc == 1 ? 16 : ramoops_ecc;
>
> +       dummy_data = NULL;
>         dummy = platform_device_register_data(NULL, "ramoops", -1,
>                                 dummy_data, sizeof(struct ramoops_platform_data));
>         if (IS_ERR(dummy)) {
>
> So I think this pdata NULL check is useful.

Fair enough. :) I've adjusted the patch a bit with some additional
pr_err()s added. It should appear in -next shortly.

Thanks!

-Kees

>
> Thanks.
>
> -Geliang
>
>> >
>> > Signed-off-by: Geliang Tang <geliangtang@...il.com>
>> > ---
>> >  fs/pstore/ram.c | 3 +++
>> >  1 file changed, 3 insertions(+)
>> >
>> > diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
>> > index 6ad831b..dd9832d 100644
>> > --- a/fs/pstore/ram.c
>> > +++ b/fs/pstore/ram.c
>> > @@ -576,6 +576,9 @@ static int ramoops_probe(struct platform_device *pdev)
>> >         if (cxt->max_dump_cnt)
>> >                 goto fail_out;
>> >
>> > +       if (!pdata)
>> > +               goto fail_out;
>> > +
>> >         if (!pdata->mem_size || (!pdata->record_size && !pdata->console_size &&
>> >                         !pdata->ftrace_size && !pdata->pmsg_size)) {
>> >                 pr_err("The memory size and the record/console size must be "
>> > --
>> > 2.7.4
>> >



-- 
Kees Cook
Nexus Security