linux-kernel - Re: Documenting ptrace access mode checking

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Message-ID: <f8069f83-f7b6-ee2c-5167-fa0d50732180@gmail.com>
Date:	Thu, 23 Jun 2016 09:06:55 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	mtk.manpages@...il.com, Jann Horn <jann@...jh.net>,
	James Morris <jmorris@...ei.org>,
	linux-man <linux-man@...r.kernel.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	lkml <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: Documenting ptrace access mode checking

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).

Cheers,

Michael

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