linux-kernel - Re: [RFC 2/2] fs,proc: Respect FMODE

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Message-ID: <CANq1E4TPPcdD-8FF_Kc=r44Vrd51Vmt-OVu+EtCC-oEzXkvJvg@mail.gmail.com>
Date:	Tue, 22 Apr 2014 17:19:42 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Andy Lutomirski <luto@...capital.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Theodore Ts'o" <tytso@....edu>
Subject: Re: [RFC 2/2] fs,proc: Respect FMODE_WRITE when opening /proc/pid/fd/N

Hi

On Tue, Apr 22, 2014 at 4:31 PM, Pavel Machek <pavel@....cz> wrote:
> Such as here?
>
> http://www.securityfocus.com/archive/1/507386

Thanks, that's the first real example someone mentioned.

Quoted from your link:

> The reopen does check the inode permission, but it does not require
> you have any reachable path to the file. Someone _might_ use that as
> a traditional unix security mechanism, but if so it's probably quite rare.

In other words, the bug you describe is that /proc/pid/fd/ allows
access to objects without a reachable path to the only _real_
filesystem link. But isn't the same true for openat()?

Thanks
David
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