linux-kernel - Re: [PATCH] proc: make proc_fd

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Date:	Tue, 27 Aug 2013 17:05:35 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Willy Tarreau <w@....eu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Brad Spengler <spender@...ecurity.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] proc: make proc_fd_permission() thread-friendly

On 08/26, Willy Tarreau wrote:
>
> On Mon, Aug 26, 2013 at 12:35:26PM -0700, Linus Torvalds wrote:
> (...)
> > Yes, it would be semantically different, but it would mean that
> > "/proc/self/fd/" would actually make sense in a way that it currently
> > does *not* - which would seem fairly important, since the primary use
> > for it tends to be /dev/stdin.
>
> I remember another user, don't know if that has changed. UPX used to build
> self-extract binaries that opened /proc/self/fd/3.

But /proc/<tgid>/fd and /proc/<tid>/fd should be the same. Unless it plays
with unshare() or clone(CLONE_THREAD /* no CLONE_FILES */).

Unlike, but:

> because it's typically a usage that
> could be discovered to be broken months after the change!

Oh yes, I agree. This change is trivial but nasty, god knows what people
actually do with /proc/self.

Oleg.

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