From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH] proc: make proc_fd_permission() thread-friendly
Date: Mon, 26 Aug 2013 20:46:31 +0200
Message-ID: <20130826184631.GA30917@redhat.com>
References: <20130824212432.GA9299@1wt.eu> <20130825052317.GZ27005@ZenIV.linux.org.uk> <20130825065039.GB9299@1wt.eu> <CA+55aFwFeCRcwn4qo570Y15mKrN3jEdN757PcZhrXs7QYi8MYA@mail.gmail.com> <20130825194844.GA16717@redhat.com> <CA+55aFzbY3zYD1i5x02Z-6K3nHKzJj6227ZBYRLqij9y0eXRqQ@mail.gmail.com> <20130826153301.GA15890@redhat.com> <20130826163704.GA21763@redhat.com> <20130826175441.GA28856@redhat.com> <87ioyspaju.fsf@xmission.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: "Eric W. Biederman" <ebiederm@xmission.com>
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On 08/26, Eric W. Biederman wrote:
>
> 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.

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.