Re: [PATCH man-pages v2 2/2] openat2.2: document new openat2(2) syscall

Aleksa Sarai
2020-03-30T09:21:12Z

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On 2020-03-30, Michael Kerrisk (man-pages) <mtk.manpages@gmail.com> wrote:
> Hello Aleksa,
>
> On 2/2/20 4:19 PM, Aleksa Sarai wrote:
> > Rather than trying to merge the new syscall documentation into open.2
> > (which would probably result in the man-page being incomprehensible),
> > instead the new syscall gets its own dedicated page with links between
> > open(2) and openat2(2) to avoid duplicating information such as the list
> > of O_* flags or common errors.
> >
> > In addition to describing all of the key flags, information about the
> > extensibility design is provided so that users can better understand why
> > they need to pass sizeof(struct open_how) and how their programs will
> > work across kernels. After some discussions with David Laight, I also
> > included explicit instructions to zero the structure to avoid issues
> > when recompiling with new headers.>
> > Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
>
> I'm just editing this page, and have a question on one piece.
>
> > +Unlike
> > +.BR openat (2),
> > +it is an error to provide
> > +.BR openat2 ()
> > +with a
> > +.I mode
> > +which contains bits other than
> > +.IR 0777 ,
>
> This piece appears not to be true, both from my reading of the
> source code, and from testing (i.e., I wrote a a small program that
> successfully called openat2() and created a file that had the
> set-UID, set-GID, and sticky bits set).
>
> Is this a bug in the implementation or a bug in the manual page text?

My bad -- it's a bug in the manual. The actual check (which does work,
there are selftests for this) is:

if (how->mode & ~S_IALLUGO)
return -EINVAL;

But when writing the man page I forgot that S_IALLUGO also includes
those bits. Do you want me to send an updated version or would you
prefer to clean it up?

--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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