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

From: Shawn Lin
Date: Wed Mar 09 2016 - 09:03:04 EST

On 2016/3/9 18:50, Jon Hunter wrote:

On 07/03/16 06:59, Shawn Lin wrote:
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

I think you should elaborate here why the behaviour between -EINVAL and
-EPERM is different as they are both errors. In other words, add your
comment about how the ADB code is checking for a supported command.

yep. So if need to send v2 after comment from Ulf, I will add more into

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@xxxxxxxxxxxxxxx
Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>

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

The change is fine with me, but I agree with Seshagiri's comment that
instead of the above, move the following test to the mmc_blk_ioctl_cmd
and mmc_blk_ioctl_multi_cmd functions:

if ((!capable(CAP_SYS_RAWIO)) || (bdev != bdev->bd_contains))
return -EPERM;

right, and both are ok to me :).
Adding this check for mmc_blk_ioctl_cmd and mmc_blk_ioctl_multi_cmd
respectively may also looks like we produce two some code sections that do the same thing.

I think it depends on how Ulf want the solution to be? Let's wait for
Ulf' comment.

There is a case statement that then would return -EINVAL if the command
is not supported.

If you look at V3 of the patch "mmc: block: Add new ioctl to send multi
commands" [0] this is how we had it and only in V4 (the final version)
did we move it.

yes, I read V3 and V4 both to see how the patch was going. Thanks for
sharing it.


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