Re: [PATCH] proc: prevent a task from writing on its own /proc/*/mem

From: Salvatore Mesoraca <s.mesoraca16@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	LSM List <linux-security-module@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Akinobu Mita <akinobu.mita@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>, Arnd Bergmann <arnd@arndb.de>,
	Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH] proc: prevent a task from writing on its own /proc/*/mem
Date: Mon, 28 May 2018 11:32:13 +0200	[thread overview]
Message-ID: <CAJHCu1Ky09DWskcD4nVW5u1C5faWMv1A4kcxWzdiap7+G1SPkg@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFx6DBp+d33_fytOGPWw11xg_L0MdGp1M2e5Obc0N9kMRQ@mail.gmail.com>

2018-05-27 3:33 GMT+02:00 Linus Torvalds <torvalds@linux-foundation.org>:
> On Sat, May 26, 2018 at 5:32 PM Kees Cook <keescook@chromium.org> wrote:
>
>> I went through some old threads from 2012 when e268337dfe26 was
>> introduced, and later when things got looked at during DirtyCOW. There
>> was discussion about removing FOLL_FORCE (in order to block writes on
>> a read-only memory region).
>
> Side note, we did that for /dev/mem, and things broke.
>
> Thus commit f511c0b17b08 "Yes, people use FOLL_FORCE ;)"
>
> Side note, that very sam ecommit f511c0b17b08 is also the explanation for
> why the patch under discussion now seems broken.
>
> People really do use "write to /proc/self/mem" as a way to keep the
> mappings read-only, but have a way to change them when required.

Oh, I didn't expect this, interesting...
A configurable LSM is probably the right way to do this.

Thank you for your time,

Salvatore