Date: Sat, 23 Feb 2013 00:03:24 -0500 From: Rich Felker <dalias@...ifal.cx> To: KOSAKI Motohiro <kosaki.motohiro@...il.com> Cc: libc-alpha <libc-alpha@...rceware.org>, musl@...ts.openwall.com Subject: Re: O_EXEC and O_SEARCH 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 > 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. Rich
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