Date: Sat, 23 Feb 2013 00:20:58 -0500 From: KOSAKI Motohiro <kosaki.motohiro@...il.com> To: Rich Felker <dalias@...ifal.cx> Cc: libc-alpha <libc-alpha@...rceware.org>, musl@...ts.openwall.com Subject: Re: O_EXEC and O_SEARCH On Sat, Feb 23, 2013 at 12:03 AM, Rich Felker <dalias@...ifal.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.
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