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SubjectRe: [Patch v3] vfs: allow file truncations when both suid and write permissions set
OGAWA Hirofumi wrote:
> Eric Paris <eparis@redhat.com> writes:
>
>
>>>> I was thinking about this and kept telling myself I was going to test v2
>>>> before I ack/nak. Clearly we shouldn't for the dropping of SUID if the
>>>> process didn't have permission to change the ATTR_SIZE.
>>>>
>>>> Acked-by: Eric Paris <eparis@redhat.com>
>>>>
>>> BTW, Do you know why doesn't security modules fix the handling of
>>> do_truncate() (i.e. ATTR_MODE | ATTR_SIZE). And why doesn't it allow to
>>> pass ATTR_FORCE for it?
>>>
>> I'm not sure what you mean. I understood ATTR_FORCE to mean 'I am magic
>> and get to override all security checks." Which is why nothing should
>> ever be using ATTR_FORCE with things other than SUID.
>>
>> I guess we could somehow force logic into the LSM to make it only apply
>> to SUID and friends but I'm not sure it buys us anything.
>>
>
> Yes, I think it's good way. Don't we want to do the following?
>
> if (permission check of job)
> return error;
> if (do job at once)
> return error;
>
> But currently way is,
>
> if (permission check of first part)
> return error
> if (do first part of job)
> return error
> if (permission check of second part)
> return error
> if (do second part of job)
> return error
>
> So, if second part was error, we may want to undo the job of first part
> in theory. But, to undo is just hard and strange.
>

Yeah, the problem is currently we don't have such wrappers, only
notify_change(). :-/



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