Re: [PATCH v2] btrfs-progs: common: make sure that qgroup id is in range

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2021/3/18 上午10:22, Sidong Yang wrote:
> On Wed, Mar 17, 2021 at 07:36:47PM +0100, David Sterba wrote:
>> On Tue, Mar 16, 2021 at 01:27:46PM +0000, Sidong Yang wrote:
>>> When user assign qgroup with qgroup id that is too big to exceeds
>>> range and invade level value, and it works without any error. but
>>> this action would be make undefined error. this code make sure that
>>> qgroup id doesn't exceed range(0 ~ 2^48-1).
>>
>> Should the level be also validate? The function parse_qgroupid does not
>> do full validation, so eg 0//0 would be parsed as a path and not as a
>> typo, level larger than 64K will be silently clamped.
>
> I agree. 0//0 would be parsed as path but it failed in
> btrfs_util_is_subvolume() and goes to err. I understand that upper 16
> bits of qgroupid is for level. so, The valid llevel range is [0~2^16-1].
> But I can't get it that level larger than 64K will be clampled.
>
> one more question about that, I see that the ioctl calls just store the
> qgroupid without any opeartion with level. is the level meaningless in
> kernel?
>
No, kernel uses the qgroup level, but it's deep in qgroup code.

In fact, kernel treats qgroupid just as an u64, and sometimes checks the
qgroup level for relationship, but under most cases, it's just a u64,
level/id doesn't really matter that much.

Thanks,
Qu