Re: [PATCH] btrfs: add BTRFS_IOC_GET_CSUMS ioctl

[Mark Harmstone <mark@harmstone.com>]

On 07/04/2026 11.39 pm, Qu Wenruo wrote:
> 
> 
> 在 2026/4/8 07:43, Boris Burkov 写道:
> [...]
>>>> We absolutely can't give non-root users csums to arbitrary data, that's
>>>> definitely a security breach.
>>>
>>> If getting csums for random logical is a security breach, I do not 
>>> think the
>>> new GET_CSUM ioctl is any better.
>>>
>>
>> Isn't it better because you have to use a file we do permissions 
>> checks on?
>>
>> So it's not an arbitrary logical, it's a logical used by a file you have
>> access to? That might still be insecure against some attack, though, what
>> do I know.
> 
> OK, that makes sense now. Although I'm still not a huge fan just to 
> combine two different tree search operations into one, just to fulfill 
> the privilege check requirement.

The privilege check is important, we are running non-root mkfs to create 
(I think) VM images. And doing two tree searches is still massively 
quicker than userspace reading the data from disk and calculating the 
csums manually.

Plus there's other potential uses for this ioctl in the future: 
something rsync-like, for instance, or for deduplication.