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Message-ID: <20130822201530.GL31117@1wt.eu>
Date: Thu, 22 Aug 2013 22:15:30 +0200
From: Willy Tarreau <w@....eu>
To: Andy Lutomirski <luto@...capital.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
"security@...nel.org" <security@...nel.org>,
Ingo Molnar <mingo@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Oleg Nesterov <oleg@...hat.com>,
Al Viro <viro@...iv.linux.org.uk>,
Linux FS Devel <linux-fsdevel@...r.kernel.org>,
Brad Spengler <spender@...ecurity.net>
Subject: Re: [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY_PATH)
On Thu, Aug 22, 2013 at 01:10:43PM -0700, Andy Lutomirski wrote:
> What's the point of nd_jump_link anyway? The only way I can think of
> for a magic symlink in /proc to point to another symlink is to open a
> symlink with O_PATH | O_NOFOLLOW. Actually trying to use the
> resulting link in /proc results in -ELOOP. (Even just trying to open
> a normal symlink with O_NOFOLLOW and without O_PATH results in
> -ELOOP.)
It's not only that, it also supports sockets and pipes that you can access
via /proc/pid/fd and not via a real symlink which would try to open eg
"pipe:[23456]" instead of the real file. So you can't get rid of it
without breaking existing apps (starting with your shell for which
/dev/stdin is a link to /proc/self/fd/0 for example).
Willy
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