Re: Documenting ptrace access mode checking

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

"Michael Kerrisk (man-pages)" [off-list ref] writes:

quoted

Hi Oleg,

On 06/22/2016 11:51 PM, Oleg Nesterov wrote:

quoted

On 06/21, Eric W. Biederman wrote:

quoted

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 ;)

quoted

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/
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