linux-kernel - Re: [PATCH v2 2/2] mmc: block: Let MMC_IOC_MULTI

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Date:   Tue, 11 Jul 2017 16:44:20 +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 2/2] mmc: block: Let MMC_IOC_MULTI_CMD return zero
 again for zero entries

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_ioctl_cmd_issue’:
>     drivers/mmc/core/block.c:630: warning: ‘ioc_err’ 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.
>
> To avoid returning an uninitialized value, and as it is pointless to do
> all this work when the MMC_IOC_MULTI_CMD ioctl is used with zero
> entries, check for this early in mmc_blk_ioctl_multi_cmd(), and return
> zero, like was returned before.
>
> Fixes: 3ecd8cf23f88d5df ("mmc: block: move multi-ioctl() to use block layer")
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>


Thanks, applied for fixes!

Kind regards
Uffe

> ---
> Should mmc_blk_ioctl_multi_cmd() return -EINVAL instead for this case?
> That would change behavior as seen from userspace, though.
>
> Feel free to fold in the previous patch if deemed appropriate.
>
> v2:
>   - No changes.
> ---
>  drivers/mmc/core/block.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index 4920ea1ece38a9b6..e0363223996e6096 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -637,6 +637,9 @@ static int mmc_blk_ioctl_multi_cmd(struct block_device *bdev,
>                            sizeof(num_of_cmds)))
>                 return -EFAULT;
>
> +       if (!num_of_cmds)
> +               return 0;
> +
>         if (num_of_cmds > MMC_IOC_MAX_CMDS)
>                 return -EINVAL;
>
> --
> 2.7.4
>