Re: [PATCH] mmc: block: fix ABI regression of mmc_blk_ioctl

[Shawn Lin <shawn.lin@rock-chips.com>]

On 2016/3/7 15:04, Seshagiri Holi wrote:
> Hi Shawn,
> 	I am not sure how why blkdev_roset is iocl function call  is landing in mmc_blk_ioctl. Could it be a IOCTL mapping issue ?
> Regards
> Seshagiri
>

Really no.
blkdev_ioctl-> case BLKROSET ->
blkdev_roset -> __blkdev_driver_ioctl ->disk->fops->ioctl

If mmc_blk_ioctl return -EINVAL, that will fails
the check of !is_unrecognized_ioctl. Then the code will continue
to work. But commit: a5f5774c55a2 ("mmc: block: Add new ioctl to send 
multi commands") changes the behaviour to check the cmd(BLKROSET) with
CAP_SYS_RAWIO firstly. So blkdev_ioctl finally get -EPERM instead of
-EINVAL. So the result you can find:

remount of /system failed;
couldn't make block device writable: Operation not permitted

openat(AT_FDCWD, "/dev/block/platform/ff420000.dwmmc/by-name/system", 
O_RDONLY) = 3 ioctl(3, BLKROSET, 0)  = -1 EPERM (Operation not permitted)

>
> -----Original Message-----
> From: Shawn Lin [mailto:shawn.lin@rock-chips.com]
> Sent: Monday, March 07, 2016 11:54 AM
> To: Ulf Hansson
> Cc: Seshagiri Holi; Jonathan Hunter; Shawn Lin; stable@vger.kernel.org; #@263.net; 4.4.x@263.net
> Subject: [PATCH] mmc: block: fix ABI regression of mmc_blk_ioctl
>
> We should return -EINVAL if cmd is not MMC_IOC_CMD or MMC_IOC_MULTI_CMD, otherwise blkdev_roset will return -EPERM.
>
> Android-adb calls make_block_device_writable with ioctl(BLKROSET), which will return error, make remount failed:
> remount of /system failed;
> couldn't make block device writable: Operation not permitted
>
> openat(AT_FDCWD, "/dev/block/platform/ff420000.dwmmc/by-name/system", O_RDONLY) = 3 ioctl(3, BLKROSET, 0)  = -1 EPERM (Operation not permitted)
>
> Fixes: a5f5774c55a2 ("mmc: block: Add new ioctl to send multi commands")
> Cc: <stable@vger.kernel.org> # 4.4.x
> Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
> ---
>
>   drivers/mmc/card/block.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c index 47bc87d..170f099 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -688,6 +688,9 @@ cmd_err:
>   static int mmc_blk_ioctl(struct block_device *bdev, fmode_t mode,
>   	unsigned int cmd, unsigned long arg)
>   {
> +	if (cmd != MMC_IOC_CMD && cmd != MMC_IOC_MULTI_CMD)
> +		return -EINVAL;
> +
>   	/*
>   	 * The caller must have CAP_SYS_RAWIO, and must be calling this on the
>   	 * whole block device, not on a partition.  This prevents overspray
> --
> 2.3.7
>
>
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-- 
Best Regards
Shawn Lin