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

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Date:	Mon, 26 Aug 2013 20:46:31 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.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

On 08/26, Eric W. Biederman wrote:
>
> 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.

Yes, and we have /proc/<tid>/ which includes fd as well.

> We might just want to have a /proc/thread symlink as well so people
> don't have this issue.

Yes! I agree.

In particular, from the changelog:

	Note: CLONE_THREAD doesn't require CLONE_FILES so task->files can
	differ,

so /proc/self/fd doesn't necessarily mean current->files, this can confuse
the application.

And I also assume that you agree with this change ;)

Oleg.

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