Re: [PATCH 01/11] block_dev: Support checking inode permissions in lookup_bdev()

[Coly Li <i@coly.li>]

On 22/12/2017 10:32 PM, Dongsu Park wrote:
> From: Seth Forshee <seth.forshee-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
> 
> When looking up a block device by path no permission check is
> done to verify that the user has access to the block device inode
> at the specified path. In some cases it may be necessary to
> check permissions towards the inode, such as allowing
> unprivileged users to mount block devices in user namespaces.
> 
> Add an argument to lookup_bdev() to optionally perform this
> permission check. A value of 0 skips the permission check and
> behaves the same as before. A non-zero value specifies the mask
> of access rights required towards the inode at the specified
> path. The check is always skipped if the user has CAP_SYS_ADMIN.
> 
> All callers of lookup_bdev() currently pass a mask of 0, so this
> patch results in no functional change. Subsequent patches will
> add permission checks where appropriate.
> 
> Patch v4 is available: https://patchwork.kernel.org/patch/8943601/
> 
> Cc: dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org
> Cc: linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
> Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: Alexander Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
> Cc: Jan Kara <jack-IBi9RG/b67k@public.gmane.org>
> Cc: Serge Hallyn <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org>
> Signed-off-by: Seth Forshee <seth.forshee-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
> Signed-off-by: Dongsu Park <dongsu-lYLaGTFnO9sWenYVfaLwtA@public.gmane.org>

Hi Dongsu,

Could you please use a macro like NO_PERMISSION_CHECK to replace hard
coded 0 ? At least for me, I don't need to check what does 0 mean in the
new lookup_bdev().

Thanks.

Coly Li

> ---
>  drivers/md/bcache/super.c |  2 +-
>  drivers/md/dm-table.c     |  2 +-
>  drivers/mtd/mtdsuper.c    |  2 +-
>  fs/block_dev.c            | 13 ++++++++++---
>  fs/quota/quota.c          |  2 +-
>  include/linux/fs.h        |  2 +-
>  6 files changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index b4d28928..acc9d56c 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -1967,7 +1967,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
>  				  sb);
>  	if (IS_ERR(bdev)) {
>  		if (bdev == ERR_PTR(-EBUSY)) {
> -			bdev = lookup_bdev(strim(path));
> +			bdev = lookup_bdev(strim(path), 0);
>  			mutex_lock(&bch_register_lock);
>  			if (!IS_ERR(bdev) && bch_is_open(bdev))
>  				err = "device already registered";
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 88130b5d..bca5eaf4 100644
[snip]


-- 
Coly Li