linux-kernel - Re: [PATCH v2] kmsg: Honor dmesg

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Message-ID: <CAGXu5jKsp6oDf=wAaPOySpDiUAeXShe4L5_LbjROHe9djp8C4Q@mail.gmail.com>
Date:	Wed, 24 Apr 2013 14:41:47 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Josh Boyer <jwboyer@...hat.com>, Kay Sievers <kay@...y.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Paris <eparis@...hat.com>,
	Christian Kujau <lists@...dbynature.de>,
	"# 3.4.x" <stable@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, Karel Zak <kzak@...hat.com>
Subject: Re: [PATCH v2] kmsg: Honor dmesg_restrict sysctl on /dev/kmsg

On Wed, Apr 24, 2013 at 2:30 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Apr 24, 2013 at 1:35 PM, Kees Cook <keescook@...omium.org> wrote:
>>
>> That said, I much prefer doing the privilege test at read time since
>> that means passing a file descriptor to another process doesn't mean
>> the new process can just continue reading.
>
> Bullshit.
>
> That's exactly the wrong kind of thinking. If you had privileges to
> open something, and you pass it off, it's *your* choice.

Yes, this is what I was pointing out originally. The semantics of
/proc/kmsg do exactly that: check at open time, which is much cleaner.

Solving the permissions checking delta between the syslog via syscall
and syslog via /proc/kmsg was the original intent of the code so that
capabilities could be dropped after open. And when /dev/kmsg came
along, it didn't follow either convention. I just want to see the
behavior standardized.

-Kees

--
Kees Cook
Chrome OS Security
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