From mboxrd@z Thu Jan  1 00:00:00 1970
From: ebiederm@xmission.com (Eric W. Biederman)
Subject: Re: [PATCH] proc: make proc_fd_permission() thread-friendly
Date: Mon, 26 Aug 2013 11:32:53 -0700
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	<20130826175441.GA28856@redhat.com>
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Cc: Andrew Morton <akpm@linux-foundation.org>,
	Willy Tarreau <w@1wt.eu>, Al Viro <viro@zeniv.linux.org.uk>,
	Andy Lutomirski <luto@amacapital.net>,
	Ingo Molnar <mingo@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	Brad Spengler <spender@grsecurity.net>,
	Linus Torvalds <torvalds@linux-foundation.org>
To: Oleg Nesterov <oleg@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20130826175441.GA28856@redhat.com> (Oleg Nesterov's message of
	"Mon, 26 Aug 2013 19:54:41 +0200")
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

Oleg Nesterov <oleg@redhat.com> writes:

> proc_fd_permission() says "process can still access /proc/self/fd
> after it has executed a setuid()", but the "task_pid() = proc_pid()
> check only helps if the task is group leader, /proc/self points to
> /proc/leader-pid.
>
> Change this check to use task_tgid() so that the whole process can
> access /proc/self/fd.

There is at least a semantic goofiness here.

There is /proc/<tgid>/fd and /proc/<tgid>/task/<pid>/fd, and the same
permission check is used by both.

We might just want to have a /proc/thread symlink as well so people
don't have this issue.  Of course that would require people to use it,
and I think the common case if people care is call gettid() and build
the path themselves.

Eric