Re: O_EXEC and O_SEARCH

[KOSAKI Motohiro <kosaki dot motohiro at gmail dot com>]

On Sat, Feb 23, 2013 at 12:03 AM, Rich Felker <dalias@aerifal.cx> wrote:
> On Fri, Feb 22, 2013 at 11:54:17PM -0500, KOSAKI Motohiro wrote:
>> > Right now, we're offering O_EXEC and O_SEARCH in musl libc, defining
>> > them as O_PATH. As long as recent Linux is used, this gives nearly
>> > correct semantics, except that combined with O_NOFOLLOW they do not
>> > fail when the final component is a symbolic link. I believe it's
>> > possible to work around this issue on sufficiently modern kernels
>> > where fstat works on O_PATH file descriptors, but adding the
>> > workaround whenever O_PATH|O_NOFOLLOW is in the flags would change the
>> > semantics when O_PATH is used by the caller rather than O_EXEC or
>> > O_SEARCH, since the value is equal. I'm not sure this is desirable.
>>
>> I have one more question. If I understand correctly, O_NOFOLLOW is
>> unspecified in
>> POSIX.
>
> Wrong.
>
>> Why do you think the current behavior is not correct?
>
>     O_NOFOLLOW
>     If path names a symbolic link, fail and set errno to [ELOOP].
>
> See http://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html

ok. this is linux kernel man pages mistake.

http://man7.org/linux/man-pages/man2/open.2.html

>  O_NOFOLLOW
>              If pathname is a symbolic link, then the open fails.  This is a
>              FreeBSD extension, which was added to Linux in version 2.1.126.
>              Symbolic links in earlier components of the pathname will still be
>              followed.


>> And, as far as I observed, current linux man pages don't tell us
>> O_PATH|O_NOFOLLOW
>> behavior. Is this really intentional result? How do you confirmed?
>
> Yes, it seems intentional. O_PATH without O_NOFOLLOW would resolve the
> symbolic link and open a file descriptor referring to the target
> inode. O_PATH|O_NOFOLLOW opens a file descriptor to the symbolic link
> inode itself. As far as I can see, this behavior is desirable and
> intentional with O_PATH but wrong for O_SEARCH or O_EXEC.

Hmm... Why?
It doesn't match linux man nor posix.