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

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Date:   Mon, 30 Mar 2020 11:36:42 +0200
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Aleksa Sarai <cyphar@...har.com>
Cc:     mtk.manpages@...il.com, Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Aleksa Sarai <asarai@...e.de>, linux-man@...r.kernel.org,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH man-pages v2 2/2] openat2.2: document new openat2(2)
 syscall

On 3/30/20 11:20 AM, Aleksa Sarai wrote:
> On 2020-03-30, Michael Kerrisk (man-pages) <mtk.manpages@...il.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@...har.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?

I'll clean it up.

So, it should say, "bits other than 07777", right?

Thanks,

Michael


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