Re: Documenting ptrace access mode checking

[Michael Kerrisk (man-pages)]

On 06/23/2016 08:56 PM, Eric W. Biederman wrote:
> "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.

Yes, good point.

Cheers,

Michael


--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/