Re: Documenting ptrace access mode checking

[Eric W. Biederman]

"Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> writes:

> Hi Oleg,
>
> On 06/22/2016 11:51 PM, Oleg Nesterov wrote:
>> On 06/21, Eric W. Biederman wrote:
>>>
>>> Adding Oleg just because he seems to do most of the ptrace related
>>> maintenance these days.
>>
>> so I have to admit that I never even tried to actually understand
>> ptrace_may_access ;)
>>
>>> We certainly need something that gives a high level view so people
>>> reading the man page can know what to expect.   If you get down into the
>>> weeds we run the danger of people beginning to think they can depend
>>> upon bugs in the implementation.
>>
>> Personally I agree. I think "man ptrace" shouldn't not tell too much
>> about kernel internals.
>
> See my other replies on this topic. Somehow, we need a way of
> describing the behavior that user-space sees. I think it's
> inevitable that that means talking about what;s going on
> "under the hood".
>
> Regarding Eric's point that "we run the danger of people beginning
> to think they can depend upon bugs in the implementation": when it
> comes to breaking the ABI, the presence or absence of documentation
> doesn't save us on that point (Linus has a few times made his position
> wrt to documentation clear).

Which are interesting in this respect as a bug in the implementation
that is a security issue can and will be changed, even if userspace
breaks.  Breaking userspace is not desirable but when there is no other
reasonable choice it will happen.

Eric