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

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Date:	Mon, 26 Aug 2013 11:32:53 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Willy Tarreau <w@....eu>, 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>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] proc: make proc_fd_permission() thread-friendly

Oleg Nesterov <oleg@...hat.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
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