linux-kernel - Re: [PATCH v2 1/2] mmc: block: Initialize ret in mmc_blk_issue_drv_op() for MMC_DRV_OP

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Message-ID: <CAPDyKFqd0BfYoVMreFMmbERRcJws7sHswbgqm2A_DswFWbcUwQ@mail.gmail.com>
Date:   Tue, 11 Jul 2017 16:44:16 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] mmc: block: Initialize ret in mmc_blk_issue_drv_op()
 for MMC_DRV_OP_IOCTL

On 5 July 2017 at 17:09, 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, for MMC_DRV_OP_IOCTL, 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.
>
> Initialize ret to zero 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>

Thanks, applied for fixes!

Kind regards
Uffe

> ---
> v2, as suggested by Arnd:
>   - Move the assignment after "case MMC_DRV_OP_IOCTL", to keep getting
>     compile-time checks on the state of the 'ret' variable,
>   - Initialize ret to zero instead of -EINVAL.
> ---
>  drivers/mmc/core/block.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index 0cfac2d391073922..4920ea1ece38a9b6 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -1182,7 +1182,7 @@ static void mmc_blk_issue_drv_op(struct mmc_queue *mq, struct request *req)
>
>         switch (mq_rq->drv_op) {
>         case MMC_DRV_OP_IOCTL:
> -               for (i = 0; i < mq_rq->ioc_count; i++) {
> +               for (i = 0, ret = 0; i < mq_rq->ioc_count; i++) {
>                         ret = __mmc_blk_ioctl_cmd(card, md, mq_rq->idata[i]);
>                         if (ret)
>                                 break;
> --
> 2.7.4
>