linux-kernel - Re: [PATCH 1/2] mmc: block: Preinitialize ret in mmc_blk_issue_drv

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Date:   Wed, 5 Jul 2017 17:07:17 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mmc: block: Preinitialize ret in mmc_blk_issue_drv_op()

Hi Arnd,

On Wed, Jul 5, 2017 at 2:06 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Wed, Jul 5, 2017 at 11:07 AM, Geert Uytterhoeven
> <geert@...ux-m68k.org> wrote:
>> With gcc 4.1.2:
>>
>>     drivers/mmc/core/block.c: In function ‘mmc_blk_issue_drv_op’:
>>     drivers/mmc/core/block.c:1178: warning: ‘ret’ may be used uninitialized in this function
>>
>> Indeed, if mq_rq->ioc_count is zero, an uninitialized value will be
>> stored in mq_rq->drv_op_result and passed to blk_end_request_all().
>>
>> Can mq_rq->ioc_count be zero?
>>   - mmc_blk_ioctl_cmd() sets ioc_count to 1, so this is safe,
>>   - mmc_blk_ioctl_multi_cmd() obtains ioc_count from user space in
>>     response to the MMC_IOC_MULTI_CMD ioctl, and does allow zero.
>>
>> Preinitialize ret to -EINVAL to fix this for current and future callers.
>>
>> Fixes: 0493f6fe5bdee8ac ("mmc: block: Move boot partition locking into a driver op")
>> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>> ---
>> I assume -EINVAL is the error we want to return here if ioc_count is
>> zero.
>> Or should it return success (zero), like mmc_blk_ioctl_multi_cmd() used
>> to do?
>
> I would suggest adding the initialization after "case MMC_DRV_OP_IOCTL:"
> instead, to keep getting compile-time checks on the state of the 'ret'
> variable. In that case, returning '0' is probably good.

Makes sense, I actually did consider that, but went with (shared) -EINVAL.

Will send v2 shortly.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds