linux-kernel - Re: [PATCHv10 man-pages 5/5] execveat.2: initial man page for execveat(2)

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Date:	Fri, 9 Jan 2015 22:57:43 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Rich Felker <dalias@...ifal.cx>
Cc:	David Drysdale <drysdale@...gle.com>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andy Lutomirski <luto@...capital.net>,
	Meredydd Luff <meredydd@...atehouse.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Hellwig <hch@...radead.org>, X86 ML <x86@...nel.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	sparclinux@...r.kernel.org
Subject: Re: [PATCHv10 man-pages 5/5] execveat.2: initial man page for
 execveat(2)

On Fri, Jan 09, 2015 at 05:42:52PM -0500, Rich Felker wrote:

> Here's a very simple way it could work -- it could put the O_PATH fd
> on a previously-unused fd number, and put a special flag on the fd,
> like FD_CLOEXEC, but that causes the kernel to close it whenever it's
> opened. The pathname passed could then simply be /dev/fd/%d or
> /proc/self/fd/%d, and although this is presently dependent on /proc
> being mounted, virtual /dev/fd/* could someday be something completely
> independent of procfs. The kernel keeps all the freedom to choose how
> to pass the name to the interpreter. I'm not proposing any kernel
> API/ABI lock-in and I'm with you in opposing such lock-in.

Huh?  open() on procfs symlinks does *NOT* work the way - the symlink is
traversed and after that point there is no information whatsoever how we
got to that vfsmount/dentry pair.  I can imagine several kludges that would
work, but they are unspeakably ugly, and do_last() is already far too
convoluted as it is.
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